Different forms of incomplete trisomy 13. Mosaicism and partial trisomy for the proximal and distal long arm

Abstract

Three cases with different forms of incomplete trisomy 13 are described; 1 was mosaic and 2 were partially trisomic for the distal and proximal long arm, respectively. The female patient who was mosaic for trisomy 13 exhibited microcephaly, minor dysmorphic features, a complex congenital heart defect, and malrotation of the intestine. The supernumerary No. 13 chromosome was present in only one fourth of blood lymphocyte and one third of skin fibroblast mitoses; her clinical picture has little in common with the usual trisomy 13 syndrome. Two sons of a mother with a balanced 13/17 translocation were found to be trisomic, one for the proximal third and the other for the distal two-thirds of the long arm of chromosome 13. The boy trisomic for the distal two-thirds showed some signs typical for the full trisomy 13 syndrome, such as stunted growth and severe mental retardation, long, incurved eyelashes, hemangiomata, and hexadactyly, whereas his brother, who is trisomic for the proximal third of the long arm of chromosome 13, presented rather unspecific clinical signs such as small chin, strabismus and nystagmus, cryptorchidism, and incurved little fingers. A review of other cases trisomic for these two segments shows that typical features of trisomy 13 are usually present in trisomy for the distal part of the long arm, and that duplication of, the proximal part leads to an unspecific clinical picture of mental retardation and minor dysmorphic traits.