Presumed disturbance of a nucleolus organizer in man: chromosome 13qs and monosomy 15 mosaicism.

Cytogenetic studies on lymphocyte and fibroblast cells from a 4 years old girl with mental impairment and multiple anomalies suggestive of a chromosomal disorder showed 2 cell-lines: all lymphocytes and 40% of the fibroblasts examined exhibited a bisatellited chromosome No. 13, and an otherwise normal karyotype. In the remaining fibroblasts a chromosome No. 15 was missing and only an early replicating minute centric fragment was present. The sequence of possible events for interpreting the child's complement as the result of a disturbance at the nucleolus organizer of chromosome 15 short arm is presented, and comparison is made with other published cases of bisatellited acrocentric chromosomes.