[DNA diagnosis of the fragile X chromosome syndrome--FRAXA using PCR]. 
Fragile X syndrome is gonosomal recessive mental retardation with the frequency 1:1000 in male population.  Fragile X syndrome is caused by amplification of CGG repeat in 1.  exon of FMT-1 gene.  The aim of this study was to set up and validate a rapid and efficient PCR diagnosis to select FRAXA negative patients in population of mental retarded patients.  In the set up phase of the method, 196 patients were diagnosed.  We were using modified radioactive PCR of CGG.  Obtained PCR fragments were separated on 6% denaturing PAGE.  Results were correlated with Southern blot analysis using pE5.1 probe.  STR-PCR was verified on a large set of patients and shows validity and efficiency of results in the case of pre- and full mutations in male hemizygous patients too.  For estimation of carriers with pre- and full mutation by females modified diagnostic approach was developed.  There was no difference found between results from PCR and Southern blot analysis.  The PCR method is convenient not only for selection of FRAXA negative patients, but for diagnosis of full mutation and premutation of affected probands.