Down syndrome with fragment X - A case report.

This article reports a case of four-month-old female infant referred to Division of Human Genetics, St. Johns' Medical College, for karyotyping with suspicion of Down syndrome. On karyotyping all analysed spreads showed trisomy 21 but a few spreads (6.66%) showed fragment X. X was broken at the centromere and both short and long arms were present in the spread. GTG bands of the two fragments correlated with the normal X counter parts. The mechanism behind isochromosome formation is discussed. Thus, this case is free trisomy 21 for Down syndrome and a mosaic for the X structural anomaly.