Distal 13q monosomy and neural tube defects.

We present a fetus with typical manifestations of distal monosomy 13q (oligodactyly, heart defect, anal atresia, hypoplastic kidneys) and der( 13)t( 1 ; 13)(q42;q21)pat. He also had exencephaly which at this developmental stage is an embryological precursor of anencephaly. Detailed analysis of neural tube defects (NTD) in publications about distal monosomy 13q showed that most defects affect cranial aspect of the neural tube (anencephaly, exencephaly, encephaloceles) with a relative small proportion of spina bifida. There are strong evidences that the gene(s) responsible for the origin of NTD in distal monosomy 13q has to be located within 13q33q34 segments. However, our analysis showed that NTD are much more common for the patients (fetuses) having larger deletions (with breakpoints at 13q22 or more proximal). These data suggest that the 13q22 segment includes a regulatory element somehow controlling function of the "distal" NTD-related gene(s).