[Martin-Bell syndrome. Improved possibilities for molecular genetic diagnosis]

In a former molecular segregation analysis of fra x mental retardation in 27 families at risk we had used marker gene probes with a relatively high recombination fraction. Thus, the resulting risk for a false diagnosis was comparatively high. To diminish this risk, all families were reanalyzed with the newly invented and more closely linked gene probes RN1A, VK23B, VK21C and U6.2. Using these probes as molecular markers we performed Southern hybridization experiments. The remaining diagnostic risk due to recombination events could be reduced to 2% up to 20% compared to preanalysis. The portion of informative families (91%) is in good agreement with the expected cumulative heterozygosis frequency of 93.4% for all 4 markers investigated. This high frequency and the very low remaining risk for a false diagnosis therefore enable a far more precise molecular diagnostic of the Martin-Bell-syndrome.