The sex chromosome‐discordant chimerism 46,XX/46,XY is rarely found in humans with a phenotypically normal appearance, and this lack of phenotypic changes and the rarity of chimerism make it difficult to identify its exact incidence. Here, we report a case of this sex chromosome‐discordant chimerism diagnosed by cytogenic and molecular analyses of peripheral blood in a phenotypically normal male who was referred to our facility for infertility. Based on the karyotype, fluorescence in situ hybridisation (FISH) and short tandem repeat (STR) analyses, the type of this chimerism was determined to be tetragametic presenting four alleles at two loci on chromosomes 16 and 21.
Although trisomy 16 is commonly detected in spontaneous abortions and accounts
for over 30% of cases of autosomal trisomy detected after spontaneous abortion,
trisomy 16 mosaicism is rarely detected by amniocentesis in the second
trimester. Here, we report a case of level III trisomy 16 mosaicism
(47,XX,+16[8]/46,XX[31]) diagnosed by cytogenetic analysis of independently
cultured amniotic fluid cells. The female baby was delivered at full term with
low birth weight and intrauterine growth retardation, and interestingly, her
karyotype was normal (46,XX). Given the difficulty in predicting the outcomes of
fetuses with this mosaicism, it is recommended to inform the possibility of
mosaicisms including this trisomy 16 mosaicism during prenatal genetic diagnosis
and genetic counseling for parents.
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