The two conditions for which population screening has been considered in obstetrics are cystic fibrosis and fragile X syndrome. More than 400 different gene mutations are known to cause cystic fibrosis. If a specific gene mutation has been identified in an affected family, individuals at risk can be screened for that particular deletion. In a low-risk family without affected members, the laboratory receives no guidance regarding the gene deletions Fragile X syndrome is the most common form of familial mental retardation. It is related to an unstable DNA region on the X chromosome.
Individuals carrying Another nonclassical inheritance pattern involves germline mosaicism.
Genomic imprinting describes a gene expression that differs according to the parent of origin. The differential expression is related to differences in DNA methylation patterns.