BACKGROUND
the 7tm  genes, also known as the hetero-trimeric gtp-binding protein -coupled receptors , are members of a large family of genes with an estimated  <dig> members in the human genome  <cit> .
these receptors are plasma membrane-bound and have evolved to respond to a large number of extracellular and chemical signals.
upon interaction with their ligands, gpcrs act through the g proteins in signaling pathways that influence physiological functions.
all gpcrs, in spite of great diversity in sequence composition, share a common protein structure.
an n-terminal extracellular domain of variable length is followed by seven hydrophobic transmembrane-helices, connected by three intracellular  and three extracellular  loops, which then terminates in a c-terminal intracellular domain  <cit> .
the functional and structural role of the different domains has been elucidated by systematic point mutations and crystal structure analysis for many of the human gpcr proteins.
several studies have collectively analyzed the occurrence, and importance of coding gpcr snps  <cit>  and also the relevance and importance of mutations within these genes for the pharmaceutical industry  <cit> .
the functional significance of thousands of point mutations has been described by a large number of investigations as evident at ncbi's pubmed central.
mutation databases dedicated to gpcr mutations are currently available online like gpcr db  <cit>  and tinygrap  <cit> .
although an extensive collection of mutations is available at these sources, the distribution of these mutations and variations within the gene or peptide, along with common snps is not easily accessible or evident.
the snp databases in public domain  have highlighted all non-synonymous snps .
also hgvbase  has further classified the location of the amino acid within the encoded proteins to more accurately predict the detrimental effects of a change in peptide sequence.
from a pharmacogenetics viewpoint, the information about natural variations within gpcr transcripts and peptides, with allele frequency and validation data and disease association, is an important, yet currently unavailable, public resource.
a database with functional promoter snp, allele frequency, peptide variation information, population and haplotype information presented in a graphically accessible format would facilitate pharmacogenomics research related to gpcr proteins.
human gpcr-db aims to provide such a public resource.
also the rate of false positive snps determined experimentally in gpcr genes is reported to be relatively high  <cit> .
for typical case-control association studies, prevailing designs favor highly polymorphic loci as against loci where the frequency of the minor allele is below 10%.
therefore more nssnps need to be validated and frequencies determined across ethnically diverse populations.
we have designed genotyping assays and attempted to validate a number of gpcr nssnps for which no validation information was available on public databases, and deposited the validation information at human gpcr-db.
we have also collected published literature snps and added to our online database.
several recent studies have focused on the subset of nssnps that most likely influence phenotype  <cit> .
comparatively, fewer attempts have been made on predicting and validating functional promoter snps  <cit> .
as a part of a parallel work, we have developed a streamlined bioinformatics and wet-lab analysis methods to identify putative functional promoter snps with up to 70% probability of influencing gene expression.
by applying this analysis package to all of the  <dig> genes in our database, we have highlighted, putative functional promoter snps.
human gpcr-db also attempts to merge snp and other variations from published articles from pubmed and online snp databases to facilitate direct identification of the functional significance of a natural variation.
RESULTS
a total of  <dig> non-redundant human gpcr peptides were obtained from swissprot of which  <dig> had swissprot id and the remaining had only trembl identifications.
also,  <dig> of the  <dig> gpcr were classified as olfactory receptors.
while all of the  <dig> entries were included in the human gpcr-db database, only non-olfactory  were considered for further analysis of gene structure, alternative transcripts, snps, and protein variations.
although the trembl entries have also been included, the data displayed for these entries would be more accurately presented in future updates of the database.
the statistical calculations for the genomic snps are based on the  <dig> non-olfactory entries, while the data for nssnps encoding peptide variations is based on  <dig> entries for which there are documented evidence for a 7-tm domain structure.
transcript information for each gene was used for calculating average exonic and intronic snps.
for genes with multiple transcript variants, the longest transcript was selected.
average number of snps per exon  of the  <dig> genes was one, while the average number of snps per intron  was nine.
however, the average number of snps per  <dig> bases of exonic sequence was twice the average number of snps per kilobase of intronic regions .
of the  <dig> genes,  <dig> were single exon genes, that is, were intronless.
the average number of exonic-snps per single-exon gene was  <dig>   while that for multi-exon genes was  <dig>  .
this observation is in agreement with earlier observation based on a smaller number of gpcrs, where, compared to intronless gpcrs, exons in genes with introns on average had fewer snps  <cit> .
of the  <dig> snps from the exons of  <dig> gpcr transcripts,  <dig> snps were coding snps, among which  <dig> were nssnp;  <dig> of which had no validation information in either of the source databases, i.e.
ncbi/dbsnp and hgvbase.
the number of validated and non-validated snps is shown in table  <dig>  by excluding genes with 'probable', 'putative', 'precursor' and other ambiguous terms as a part of their description , we reduced the number of snps from  <dig> to  <dig> non-validated, nssnps which were considered as our list of prime candidates for the wet-lab validation process .
as a part of our first stage validation process, we designed assays for  <dig> of the  <dig> snps in gpcr genes of interest based on our better understanding of their role in human disease and physiology.
finally, of the  <dig> assayed snps,  <dig> were found to be polymorphic in our nordic population sample consisting of dna from  <dig> un-related healthy individuals.
of the  <dig> polymorphic markers  <dig> had a minor allele frequency higher than 10%.
the number of synonymous and non-synonymous snps and those with validation information, as deposited at ncbi/dbsnp, during 2003– <dig>
the initial  <dig> gpcrs were selected as per annotation by ensembl.
support for structural evidence of  <dig> gpcrs was obtained from swissprot.
classification of gpcrs was obtained from gpcrdb , ensembl , international union of pharmacology .
according to the international union of pharmacology ,  <dig> gpcrs from  <dig> were categorized either as 'peptide receptors'  or 'chemokine receptors'  or 'monoamine receptors' .
the distribution of nssnps across the  <dig> structural and functional domains  of these  <dig> gpcrs was calculated .
these  <dig> gpcrs have in total  <dig> nssnps, of which  <dig> snps have validation information in the major public databases.
to these  <dig> snps we added  <dig> snps from published pubmed sources  <cit> , bringing the total number of validated snps, used for this analysis, to  <dig> snp.
the  <dig> snps validated in this study were not included for this analysis since we wanted to analyze publicly available data only, at this time.
the distribution of nssnp numbers was compared between individual groups  and in various combinations with other two groups .
none of the groups of receptors deviated from the mean of the three groups together, in any significant way.
the n-terminus and external-loop snps were then combined in one group, and c-terminus and internal-loop snps in another group, and compared with nssnps in tm region.
the nssnp distribution in the three domains approached significance  in the monoamine sub-group of gpcrs.
we then calculated the average number of nssnp per  <dig> bases of each of the  <dig> domains.
the average number of nssnps in the tm region of monoamine receptors  was half of the average for each of the other groups .
this difference was not observed for any of the other four  structural domains of the peptides .
total number of nssnp in various domains of  <dig> subgroups of gpcr proteins.
abbreviations: n-term : n terminus; c-term : c terminus; i-loop : internal loops; e-loop : external loops; tm: trans-membrane.
the numbers in the brackets are the average number of snps per  <dig> base pairs of a specific domain.
the fisher's exact p-values were calculated using a  <dig> ×  <dig> contingency table at .
contingency tables of  <dig> ×  <dig> were constructed at .
p-values of below or close to  <dig>  are considered significant.
we compiled together the functional properties of peptide variations from published records along with the knowledge of the location and the two alleles of a nssnp in our database.
searching pubmed records, we found  <dig> nssnps located in the precise position, and substituting the same amino acid, as those studied for functional analysis shown in table  <dig> .
database interface and layout
the human gpcr-db is currently online .
this database allows for  <dig> alternative queries, either ensembl gene id, or swissprot/trembl id or part of the gene name or description.
resulting hits are displayed along with total number of coding snps and protein variations.
these links in turn display a graphic representation of the snp locations within exons  and the query gene.
the exons are drawn in proportion to the largest exon, while the introns are of fixed length.
the snp list provides allele information, flanking sequences  and links for validation information and source databases.
the promoter information is drawn in a similar manner, with mouse conserved regions indicated with green bars underneath and snps within conserved regions marked with a symbol 'm' in the snp full-list.
snps predicted to influence protein binding according to our prediction model are marked 't' in the snp full-list.
the link for protein variations displays a window with snp, marked in red arrows, and mutation distribution across  <dig> regions of the peptide; n-terminus, c-terminus and trans-membrane and loop regions.
association with diseases and the corresponding pubmed id are displayed as a popup menu following the link under 'disease' column.
discussion
we have constructed a database, which combines mutation information with validated snp information from publicly available sources.
we have then attempted to validate and determine the frequencies of  <dig> of the  <dig> non-synonymous snps for which no validation information was available publicly.
proportion of true polymorphic loci was 20%, in agreement with reported expectations from several studies  <cit> .
the statistical approach for the analysis of distribution of natural variations in gpcrs, presented here is borrowed from two recent studies  <cit> .
while in the first of these studies  <cit>   <dig> gpcr genes were sequenced in  <dig> individuals of divergent ethnic backgrounds and resulting frequency distribution of nssnps were compared with non-gpcr genes, the later study  <cit>  analyzed differences in distribution of published and publicly available nssnp in  <dig> gpcr genes, across the  <dig> peptide domains.
for our current report we analyzed  <dig> gpcr genes with over  <dig> nssnps   <cit> .
transcripts lacking introns had on average higher density of snps  than those with introns, in agreement with an earlier published report  <cit> .
the distribution of the nssnp in the  <dig> different peptide domains  was found not to be different between any of the ligand specific sub-groups of gpcr proteins, namely peptide receptors, monoamine receptors and chemokine receptors.
we reasoned that the evolutionary constraints on outer- and inner-loops along with the n-term and c-term regions would be related to the function of these regions while the constraints on the trans-membrane regions might be related to their structure.
we, therefore compared the distribution of validated nssnp in the  <dig> major peptide domains .
we observed a difference in nssnp distribution across the three regions, which approached significance .
there was a two-fold decrease in frequency of occurrence of nssnp in the tm region of monoamine receptors as compared to the other sub-groups of receptors.
this indicates that there might perhaps be a functional selection against variations, acting on tm domains of monoamine receptors, which is less selective on the tm domains of peptide receptors, and chemokine receptor gpcrs.
a recent study reported differences between the distribution of 'disease causing' and 'non-disease causing' variations in different sub-groups of gpcr family members  <cit> .
our study excluded rare mutations, which were known to be associated with disease, and therefore a similar comparison was not possible.
although human gpcr-db database does obtain the bulk of the information and data from ensembl and dbsnp, it is not merely a subset of these major databases.
while ensembl provides sequence and genetic variation information, it provides snp validation information obtained from public sources, which may include, as shown in several published studies, up to 50% false positives.
ncbi's dbsnp provides validation-, submitter- and method-information, yet rates of false positives have proven to be high.
these databases harbor information of genetic variations for all coding and non-coding regions of the human genome.
the human gpcr-db, in addition to providing this set of information, provides in-house validation and assay-information for non-validated nssnps.
human gpcr-db provides natural variation, mutation, promoter- and peptide-variation information along with gene structure and peptide 7-tm structure information and snp validation information of a focused group of clinically important genes.
transcriptional regulatory regions on the 5'-fr of human genes encode short sequences which serve as targets for binding of transcription factors .
eukaryotic tfs tolerate considerable sequence variation in their target sites and recent works in bioinformatics  <cit>  have developed reliable methods to model the dna binding specificity of individual tfs  <cit> .
currently the most successful approach to overcome this information gap is based on the assumption that gene sequences conserved between species  would most likely mediate biological function  <cit> .
our recent study  describes a method for the detection and validation of functionally important snps in the 5'-flanking regions of human.
the rate of successful detection of snps influencing tfbs using our method is approximately 70%.
this prediction algorithm has been used to highlight snps in 5' flanking regions of the gpcr in the human gpcr-db genes to facilitate selection and study of functionally important promoter snps.
the knowledge of functional promoter snps would help us study disease related gpcr in more details.
the functional domains of human gpcrs have over the passed decade been dissected by systematically mutating the peptide sequence  <cit> .
a collection of mutations and their disease significance and influence on the function of the protein together with common variations within the human population would facilitate our understanding of the variations and disease association.
human gpcr-db attempts to merge snp and mutation information along with disease information in easily accessible and user-friendly manner.
although direct links to disease databases would be included in the next release, the existing information about the source publication can be helpful in obtaining the relevant details about the mutations.
current and future updates
of the  <dig> nssnps without validation information, we have currently validated  <dig> snps.
future updates would include information about the remaining nssnps, and any additional which are reported by public databases.
we have also collected  <dig> published snps, which have as yet not been deposited at public databases, or are in the process of being deposited.
we would have a complete update of snp data for every new release of ncbi and hgvbase snp tables.
new gpcr identification and characterization, or changes in existing gpcr genes or proteins information would be updated once a year from ensembl and swissprot databases.
pubmed references would be updated monthly or as often as necessary to complete the mutation coverage of the  <dig> gpcr proteins.
haplotype information and genetic association studies for available snps along with published records on functional promoter snps would be added.
a valuable addition would be to indicate variation frequencies in ethnically diverse populations.
we are currently adding such information about the allele frequencies and populations in the database and would be provided in future updates.
CONCLUSIONS
single-exon gpcrs on average have approximately three times the number of snps as compared to gpcrs with introns.
among various functional classes of gpcrs, monoamine gprcs have lower number of natural variations within the trans-membrane domain indicating evolutionary selection against non-synonymous changes within membrane localizing domain.
the human gpcr-db compiles snps and mutations in one database.
using a recently developed method for identification of functionally important snps in the 5'-flanking regions of human, with approximately 70% success rate, the database highlights such snps to facilitate selection and study of functionally important promoter snps.

 the 7tm genes, also known as the hetero-trimeric gtp-binding protein -coupled receptors, are members of a large family of genes with an estimated members in the human genome. these receptors are plasma membrane-bound and have evolved to respond to a large number of extracellular and chemical signals. upon interaction with their ligands, gpcrs act through the g proteins in signaling pathways that influence physiological functions. all gpcrs, in spite of great diversity in sequence composition, share a common protein structure. an n-terminal extracellular domain of variable length is followed by seven hydrophobic transmembrane-helices, connected by three intracellular and three extracellular loops, which then terminates in a c-terminal intracellular domain. the functional and structural role of the different domains has been elucidated by systematic point mutations and crystal structure analysis for many of the human gpcr proteins. several studies have collectively analyzed the occurrence, and importance of coding gpcr snps and also the relevance and importance of mutations within these genes for the pharmaceutical industry. the functional significance of thousands of point mutations has been described by a large number of investigations as evident at ncbi's pubmed central. mutation databases dedicated to gpcr mutations are currently available online like gpcr db and tinygrap. although an extensive collection of mutations is available at these sources, the distribution of these mutations and variations within the gene or peptide, along with common snps is not easily accessible or evident. the snp databases in public domain have highlighted all non-synonymous snps. also hgvbase has further classified the location of the amino acid within the encoded proteins to more accurately predict the detrimental effects of a change in peptide sequence. from a pharmacogenetics viewpoint, the information about natural variations within gpcr transcripts and peptides, with allele frequency and validation data and disease association, is an important, yet currently unavailable, public resource. a database with functional promoter snp, allele frequency, peptide variation information, population and haplotype information presented in a graphically accessible format would facilitate pharmacogenomics research related to gpcr proteins. human gpcr-db aims to provide such a public resource. also the rate of false positive snps determined experimentally in gpcr genes is reported to be relatively high. for typical case-control association studies, prevailing designs favor highly polymorphic loci as against loci where the frequency of the minor allele is below 10%. therefore more nssnps need to be validated and frequencies determined across ethnically diverse populations. we have designed genotyping assays and attempted to validate a number of gpcr nssnps for which no validation information was available on public databases, and deposited the validation information at human gpcr-db. we have also collected published literature snps and added to our online database. several recent studies have focused on the subset of nssnps that most likely influence phenotype. comparatively, fewer attempts have been made on predicting and validating functional promoter snps. as a part of a parallel work, we have developed a streamlined bioinformatics and wet-lab analysis methods to identify putative functional promoter snps with up to 70% probability of influencing gene expression. by applying this analysis package to all of the genes in our database, we have highlighted, putative functional promoter snps. human gpcr-db also attempts to merge snp and other variations from published articles from pubmed and online snp databases to facilitate direct identification of the functional significance of a natural variation.  a total of non-redundant human gpcr peptides were obtained from swissprot of which had swissprot id and the remaining had only trembl identifications. also, of the gpcr were classified as olfactory receptors. while all of the entries were included in the human gpcr-db database, only non-olfactory were considered for further analysis of gene structure, alternative transcripts, snps, and protein variations. although the trembl entries have also been included, the data displayed for these entries would be more accurately presented in future updates of the database. the statistical calculations for the genomic snps are based on the non-olfactory entries, while the data for nssnps encoding peptide variations is based on entries for which there are documented evidence for a 7-tm domain structure. transcript information for each gene was used for calculating average exonic and intronic snps. for genes with multiple transcript variants, the longest transcript was selected. average number of snps per exon of the genes was one, while the average number of snps per intron was nine. however, the average number of snps per bases of exonic sequence was twice the average number of snps per kilobase of intronic regions. of the genes, were single exon genes, that is, were intronless. the average number of exonic-snps per single-exon gene was while that for multi-exon genes was. this observation is in agreement with earlier observation based on a smaller number of gpcrs, where, compared to intronless gpcrs, exons in genes with introns on average had fewer snps. of the snps from the exons of gpcr transcripts, snps were coding snps, among which were nssnp; of which had no validation information in either of the source databases, i.e. ncbi/dbsnp and hgvbase. the number of validated and non-validated snps is shown in table by excluding genes with'probable','putative','precursor' and other ambiguous terms as a part of their description, we reduced the number of snps from to non-validated, nssnps which were considered as our list of prime candidates for the wet-lab validation process. as a part of our first stage validation process, we designed assays for of the snps in gpcr genes of interest based on our better understanding of their role in human disease and physiology. finally, of the assayed snps, were found to be polymorphic in our nordic population sample consisting of dna from un-related healthy individuals. of the polymorphic markers had a minor allele frequency higher than 10%. the number of synonymous and non-synonymous snps and those with validation information, as deposited at ncbi/dbsnp, during 2003– the initial gpcrs were selected as per annotation by ensembl. support for structural evidence of gpcrs was obtained from swissprot. classification of gpcrs was obtained from gpcrdb, ensembl, international union of pharmacology. according to the international union of pharmacology, gpcrs from were categorized either as'peptide receptors' or'chemokine receptors' or'monoamine receptors'. the distribution of nssnps across the structural and functional domains of these gpcrs was calculated. these gpcrs have in total nssnps, of which snps have validation information in the major public databases. to these snps we added snps from published pubmed sources, bringing the total number of validated snps, used for this analysis, to snp. the snps validated in this study were not included for this analysis since we wanted to analyze publicly available data only, at this time. the distribution of nssnp numbers was compared between individual groups and in various combinations with other two groups. none of the groups of receptors deviated from the mean of the three groups together, in any significant way. the n-terminus and external-loop snps were then combined in one group, and c-terminus and internal-loop snps in another group, and compared with nssnps in tm region. the nssnp distribution in the three domains approached significance in the monoamine sub-group of gpcrs. we then calculated the average number of nssnp per bases of each of the domains. the average number of nssnps in the tm region of monoamine receptors was half of the average for each of the other groups. this difference was not observed for any of the other four structural domains of the peptides. total number of nssnp in various domains of subgroups of gpcr proteins. abbreviations: n-term: n terminus; c-term: c terminus; i-loop: internal loops; e-loop: external loops; tm: trans-membrane. the numbers in the brackets are the average number of snps per base pairs of a specific domain. the fisher's exact p-values were calculated using a × contingency table at. contingency tables of × were constructed at. p-values of below or close to are considered significant. we compiled together the functional properties of peptide variations from published records along with the knowledge of the location and the two alleles of a nssnp in our database. searching pubmed records, we found nssnps located in the precise position, and substituting the same amino acid, as those studied for functional analysis shown in table. database interface and layout the human gpcr-db is currently online. this database allows for alternative queries, either ensembl gene id, or swissprot/trembl id or part of the gene name or description. resulting hits are displayed along with total number of coding snps and protein variations. these links in turn display a graphic representation of the snp locations within exons and the query gene. the exons are drawn in proportion to the largest exon, while the introns are of fixed length. the snp list provides allele information, flanking sequences and links for validation information and source databases. the promoter information is drawn in a similar manner, with mouse conserved regions indicated with green bars underneath and snps within conserved regions marked with a symbol'm' in the snp full-list. snps predicted to influence protein binding according to our prediction model are marked't' in the snp full-list. the link for protein variations displays a window with snp, marked in red arrows, and mutation distribution across regions of the peptide; n-terminus, c-terminus and trans-membrane and loop regions. association with diseases and the corresponding pubmed id are displayed as a popup menu following the link under'disease' column. discussion we have constructed a database, which combines mutation information with validated snp information from publicly available sources. we have then attempted to validate and determine the frequencies of of the non-synonymous snps for which no validation information was available publicly. proportion of true polymorphic loci was 20%, in agreement with reported expectations from several studies. the statistical approach for the analysis of distribution of natural variations in gpcrs, presented here is borrowed from two recent studies. while in the first of these studies gpcr genes were sequenced in individuals of divergent ethnic backgrounds and resulting frequency distribution of nssnps were compared with non-gpcr genes, the later study analyzed differences in distribution of published and publicly available nssnp in gpcr genes, across the peptide domains. for our current report we analyzed gpcr genes with over nssnps. transcripts lacking introns had on average higher density of snps than those with introns, in agreement with an earlier published report. the distribution of the nssnp in the different peptide domains was found not to be different between any of the ligand specific sub-groups of gpcr proteins, namely peptide receptors, monoamine receptors and chemokine receptors. we reasoned that the evolutionary constraints on outer- and inner-loops along with the n-term and c-term regions would be related to the function of these regions while the constraints on the trans-membrane regions might be related to their structure. we, therefore compared the distribution of validated nssnp in the major peptide domains. we observed a difference in nssnp distribution across the three regions, which approached significance. there was a two-fold decrease in frequency of occurrence of nssnp in the tm region of monoamine receptors as compared to the other sub-groups of receptors. this indicates that there might perhaps be a functional selection against variations, acting on tm domains of monoamine receptors, which is less selective on the tm domains of peptide receptors, and chemokine receptor gpcrs. a recent study reported differences between the distribution of'disease causing' and'non-disease causing' variations in different sub-groups of gpcr family members. our study excluded rare mutations, which were known to be associated with disease, and therefore a similar comparison was not possible. although human gpcr-db database does obtain the bulk of the information and data from ensembl and dbsnp, it is not merely a subset of these major databases. while ensembl provides sequence and genetic variation information, it provides snp validation information obtained from public sources, which may include, as shown in several published studies, up to 50% false positives. ncbi's dbsnp provides validation-, submitter- and method-information, yet rates of false positives have proven to be high. these databases harbor information of genetic variations for all coding and non-coding regions of the human genome. the human gpcr-db, in addition to providing this set of information, provides in-house validation and assay-information for non-validated nssnps. human gpcr-db provides natural variation, mutation, promoter- and peptide-variation information along with gene structure and peptide 7-tm structure information and snp validation information of a focused group of clinically important genes. transcriptional regulatory regions on the 5'-fr of human genes encode short sequences which serve as targets for binding of transcription factors. eukaryotic tfs tolerate considerable sequence variation in their target sites and recent works in bioinformatics have developed reliable methods to model the dna binding specificity of individual tfs. currently the most successful approach to overcome this information gap is based on the assumption that gene sequences conserved between species would most likely mediate biological function. our recent study describes a method for the detection and validation of functionally important snps in the 5'-flanking regions of human. the rate of successful detection of snps influencing tfbs using our method is approximately 70%. this prediction algorithm has been used to highlight snps in 5' flanking regions of the gpcr in the human gpcr-db genes to facilitate selection and study of functionally important promoter snps. the knowledge of functional promoter snps would help us study disease related gpcr in more details. the functional domains of human gpcrs have over the passed decade been dissected by systematically mutating the peptide sequence. a collection of mutations and their disease significance and influence on the function of the protein together with common variations within the human population would facilitate our understanding of the variations and disease association. human gpcr-db attempts to merge snp and mutation information along with disease information in easily accessible and user-friendly manner. although direct links to disease databases would be included in the next release, the existing information about the source publication can be helpful in obtaining the relevant details about the mutations. current and future updates of the nssnps without validation information, we have currently validated snps. future updates would include information about the remaining nssnps, and any additional which are reported by public databases. we have also collected published snps, which have as yet not been deposited at public databases, or are in the process of being deposited. we would have a complete update of snp data for every new release of ncbi and hgvbase snp tables. new gpcr identification and characterization, or changes in existing gpcr genes or proteins information would be updated once a year from ensembl and swissprot databases. pubmed references would be updated monthly or as often as necessary to complete the mutation coverage of the gpcr proteins. haplotype information and genetic association studies for available snps along with published records on functional promoter snps would be added. a valuable addition would be to indicate variation frequencies in ethnically diverse populations. we are currently adding such information about the allele frequencies and populations in the database and would be provided in future updates.  single-exon gpcrs on average have approximately three times the number of snps as compared to gpcrs with introns. among various functional classes of gpcrs, monoamine gprcs have lower number of natural variations within the trans-membrane domain indicating evolutionary selection against non-synonymous changes within membrane localizing domain. the human gpcr-db compiles snps and mutations in one database. using a recently developed method for identification of functionally important snps in the 5'-flanking regions of human, with approximately 70% success rate, the database highlights such snps to facilitate selection and study of functionally important promoter snps. 
single-exon gpcrs on average have approximately three times the number of snps as compared to gpcrs with introns. the average number of exonic-snps per single-exon gene was while that for multi-exon genes was. the average number of snps per bases of exonic sequence was found to be twice the average number of snps per kilobase of intronic regions. of the genes, were single exon genes, that is, were intronless. among various functional classes of gpcrs, monoamine gprcs have lower number of natural variations within the trans-membrane domain indicating evolutionary selection against non-synonymous changes within the membrane-localizing domain of this sub-class of gpcrs. the average number of variations within the different protein domain indicates a lower rate of variation in the trans-membrane region of monoamine gpcrs, as compared to chemokine- and peptide-receptor sub-classes of gpcrs. in a sample of chromosomes from a nordic population, we attempted to determine the allele frequencies of non-synonymous snps, and found novel polymorphic markers. natural variation and rare mutation information were merged and presented online in the human gpcr-db database.
 we have surveyed, compiled and annotated nucleotide variations in human 7-transmembrane receptors. in a sample of chromosomes from a nordic population, we attempted to determine the allele frequencies of non-synonymous snps, and found novel polymorphic markers. gpcr receptors of physiological and clinical importance were prioritized for statistical analysis. natural variation and rare mutation information were merged and presented online in the human gpcr-db database.  the average number of snps per bases of exonic sequence was found to be twice the average number of snps per kilobase of intronic regions. of the genes, were single exon genes, that is, were intronless. the average number of exonic-snps per single-exon gene was while that for multi-exon genes was. the average number of variations within the different protein domain indicates a lower rate of variation in the trans-membrane region of monoamine gpcrs, as compared to chemokine- and peptide-receptor sub-classes of gpcrs.  single-exon gpcrs on average have approximately three times the number of snps as compared to gpcrs with introns. among various functional classes of gpcrs, monoamine gprcs have lower number of natural variations within the trans-membrane domain indicating evolutionary selection against non-synonymous changes within the membrane-localizing domain of this sub-class of gpcrs. 