From new screens to discovered genes: the successful past and promising present of single gene disorders.

Prenatal screening for single gene disorders, which include over 10,000 diverse diseases, presents a great challenge. The major approach to identifying high-risk groups for diseases, from Tay Sachs Disease to sickle cell disease, has historically centered on ethnic-based screening. A major concern in an ethnic-based approach is that carriers belonging to less-traditionally considered populations will be missed. In the United States, the paradigm for a more modern pan-ethnic approach has become exemplified by cystic fibrosis (CF), although considerable debate about future directions remains. CF screening brings several additional issues to the forefront, including that the largest molecular prenatal genetic screening program is based on a single gene disorder that is not necessarily severely disabling. On the other hand, several devastating disorders where screening is indeed available remain relatively inaccessible to prenatal patients in the general population. Future candidates to consider for broad-based screening programs include spinal muscular atrophy (SMA), fragile X, and inborn errors of metabolism. As prenatal screening for single gene disorders expands, issues to consider include inclusion criteria and risk versus benefit.