Case Report - 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

A novel human sex-determining gene linked to Xp11.21-11.23

Context: The molecular basis for about 70-80% of 46,XY sex-reversed females remains unexplained, because they carry normal copies of the genes (SRY, SOX9, DAX1, DMRT, SF1, WT1) involved in sex determination pathway. Objective: The objective of this study is to map the chromosomal locus responsible for an unexplained sex-reversed phenotype. Design: The study implemented a genome-wide scan using families with multiple sex-reversed individuals. Setting: The patients, along with the family members, were selected from different hospitals/reproductive centers. Participants: Sex-reversed individuals and their siblings and parents participated in the study. Main Outcome Measures: Identification of the chromosomal locus responsible for sex reversal in these families and sequence analysis of candidate genes were the main outcome measures. Results: Parametric linkage analysis revealed a maximum two-point LOD score of 5.70 with marker DXS991 (Xp11.21) and 4.57 with marker DXS1039 (Xp11.23-Xp11.22), and a multipoint LOD score of 5.77 with marker DXS991 and 5.22 with marker DXS1039. The two markers (DXS991 and DXS1039) with highest LOD score span approximately 3.41 cM (75.79-79.2 cM) on the short arm of the X-chromosome. Conclusion: Our findings provide evidence for a major susceptibility locus for sex reversal/gonadal dysgenesis on the short arm of the X-chromosome (Xp11.21-11.23). Furthermore, molecular exploration of the expression of candidate genes in the embryonic gonad/gonadal ridge will help in the identification of the underlying gene for sex reversal