Abstract for presentation at 11th International Congress of Human Genetics

Purpose: Here we show some data from the patient of developmental delay and pigment dysplasia with chromosomal translocation between Xq and 15p. He has 15p small deletion and large additional Xq containing XIST on the arm. If XIST works only on Xq in derivative chromosome restrictedly, he should be asymptomatic. From his phenotype we assume that the gene functions on 15q in derivative chromosome should be impaired. Now we investigated the change of OCA2 gene expression on 15q. We confirmed that his OCA2 expression was decreased in half compared to control. It would be the clue for poly-gene inactivation on 15q in the derivative chromosome.
Methods: He was born with hypotonia, multiple congenital anomalies, and pigmental dysplasia. His karyotype was 46, XY, der (15) t(X; 15) (q13; p11.2) by G-band chromosome analysis. We used peripheral blood lymphocyte and lymph blast cell line of patient and parents. R-band chromosome analysis and methylation sensitive PCR analysis were done in standard methods. Gene expressions were measured with ABI7700 using quantitative RT-PCR. We investigated the expressions of three genes, XIST, OCA2, and GAPDH.
Results: R-band chromosome analysis showed replication delay in derivative chromosome including whole Xq and some 15q region, which suggests predominant inactivation in derivative chromosome. Also it may imply the 15q autosomal inactivation in the derivative chromosome. Methylation sensitive PCR confirmed predominant inactivation on derivative chromosome. In expression analysis XIST was detected in patient and mother. The OCA2 gene was expressed in all cell lines but expression in the patient was far less than that of parents’.
Conclusions Considering the patterns of XIST expression, and Xq and 15q inactivation, decreased OCA2 expression on 15q in the patient might be caused by X chromosome rearrangement.