Difficulty in showing mosaicism in the mother of three mongols.

Parental mosaicism for trisomy-21 is a recognized reason for the birth of mongol children, and the possibility of parental mosaicism may be suspected especially in couples who produce more than one 'regular' mongol. However, in a recent review, Richards (1970) found only 11 documented instances of this occurrence. We wish to describe another woman in whom mosaicism was suspected clinically but was difficult to show by chromosome studies. Findings This family presented for investigation at the Royal Children's Hospital in 1963 because the parents had two mongol children. The family pedigree is shown in the Fig. Chromosome studies were carried out at this time on the children, parents, and relatives as indicated. The two mongol children and the matemal uncle were shown to have regular trisomy-G and all the other relatives studied were normal. The results obtained in the abnormal individuals are shown in the Table. The mother was short in stature and borderline in intelligence, and her facial appearance and head shape strongly suggested mongolism. A second blood sample and a bone marrow sample were therefore examined in an endeavour to find some trisomic cells. Unfortunately, a skin biopsy failed to grow. Even though mosaicism was not shown, it was considered so likely that the parents were told that the chance of I