Multiplex FISH telomere integrity assay identifies an unbalanced cryptic translocation der(5)t(3;5) (q27;p15.3) in a family with three mentally retarded individuals

Cryptic rearrangements involving the terminal regions of chromosomes are su spected to be the cause of idiopathic mental retardation in a significant n umber of cases. This finding highlights the necessity of a primary screenin g test for such chromosome aberrations. Here we present a multiplex fluores cence in situ hybridization telomere integrity assay which allows the detec tion of submicroscopic aberrations in the telomeric regions of all chromoso mes, This novel approach identified an unbalanced cryptic translocation der (5)t(3;5)(q27;p15.3) in a family with three cases of unexplained mental ret ardation and dysmorphic features. The symptoms of the patients represent ne ither the classical dup(3q)- nor cri du chat syndrome, although all affecte d individuals demonstrate several features of both syndromes. The identific ation of two balanced translocation carriers emphasizes the significance of the telomere integrity assay for genetic counseling and prenatal diagnosis .