Segregation of acrocentric chromosome association in familial dicentric Robertsonian translocation t(14p;22p), aneuploidy (trisomy-21) and heteromorphism.

The frequency and types of acrocentric chromosome association were quantitatively analysed in a Down syndrome child with unusual karyotype, 46, XX, -14, -22, t dic (14p;22p), +21, 21S+. Father and 4 sibs were heterozygous carriers for t dic (14p;22p). The variant 21S+ was inherited from the mother. The occurrence of translocation and trisomy in the same individual is extremely rare. Acrocentric chromosome association was analysed in this interesting family to understand the interrelationship of acrocentric chromosome association, Robertsonian translocation and heteromorphism, as possible predisposing factors for nondisjunction. Our findings suggest that acrocentric chromosome association is a heritable and nonrandom phenomenon. Heterozygous carriers for translocations and variants are likely to be at increased risk of nondisjunction. Long term family studies will enable to ascertain the causal-relationship of these factors more precisely.

Familial fragile secondary constriction on chromosome 2 (2q11) with unusual features and psychomotor retardation.

A child with fragile secondary constriction 2q11 associated with unusual clinical features and psychomotor retardation is described. The pathogenetic significance of this fragile site still remains unclear, and heterogeneity of clinical manifestations is not well understood.