Wp. Robinson et al., MOLECULAR STUDIES OF CHROMOSOMAL MOSAICISM - RELATIVE FREQUENCY OF CHROMOSOME GAIN OR LOSS AND POSSIBLE ROLE OF CELL SELECTION, American journal of human genetics, 56(2), 1995, pp. 444-451
Studies of uniparental disomy and origin of nonmosaic trisomies indica
te that both gain and loss of a chromosome can occur after fertilizati
on. It is therefore of interest to determine both the relative frequen
cy with which gain or loss can contribute to chromosomal mosaicism and
whether these frequencies are influenced by selective factors. Thirty
-two mosaic cases were examined with molecular markers, to try to dete
rmine which was the primary and which was the secondary cell line: 16
cases of disomy/trisomy mosaicism (5 trisomy 8, 2 trisomy 13, 1 trisom
y 18, 4 trisomy 21, and 4 involving the X chromosome), 14 cases of 45,
X/46,XX, and 2 cases of 45,X/47,XXX. Of the 14 cases of mosaic 45,X/46
,XX, chromosome loss from a normal disomic fertilization predominated,
supporting the hypothesis that 45,X might be compatible with survival
only when the 45,X cell line arises relatively late in development. M
ost cases of disomy/trisomy mosaicism involving chromosomes 13, 18, 21
, and X were also frequently associated with somatic loss of one (or m
ore) chromosome, in these cases from a trisomic fertilization. By cont
rast, four of the five trisomy 8 cases were consistent with a somatic
gain of a chromosome 8 during development from a normal zygote. It is
possible that survival of trisomy 8 is also much more likely when the
aneuploid cell line arises relatively late in development.