Familial Robertsonian Translocation rob(14;21) and Elevated Risk for Translocation Trisomy 21 Down Syndrome

A large Omani family with unusually high recurrence of translocation trisomy 21 (five of nine offspring) was studied using microsatellite and whole-genome sequencing analysis to characterize meiotic nondisjunction patterns. All affected cases showed nondisjunction at meiosis I with distinctive crossover patterns on chromosome 21, differing from typical free trisomy 21 inheritance, though no novel pathogenic variants were identified in the carrier mother.