Subtle phenotypic effects of mosaic trisomy X in monozygotic twins with Prader-Willi syndrome: case report and review of literature

Background: We described the first monozygotic twins with 46, XX/47, XXX mosaicism and Prader-Willi syndrome, who were manifested with typical Prader-Willi syndrome (PWS) symptoms and slight trisomy X characteristics. Trisomy X symptoms can differentiate greatly, ranging from no significant manifest to special appearance, whereas 46, XX/47, XXX mosaicism may be rather inapparent. Case presentation The twin girls (B1 and B2) were born with weak cry, axial hypotonia, sucking difficulties and PWS facial appearance. They were also manifested with clinodactyly, inappropriate low birth weight, epicanthal folds and congenital heart disease, too atypical to be likely caused by PWS alone and indicating an associated problem. The diagnosis of 46, XX/47, XXX mosaicism and Prader-Willi syndrome was established based on clinical suspicion and molecular analysis. Therapy were conducted, followed by 4 years’ follow-up. Conclusions This report illustrates the first monozygotic twins with 46, XX/47, XXX mosaicism and Prader-Willi syndrome. Subtle phenotypic effects of mosaic trisomy X in monozygotic twins with Prader-Willi syndrome may be significance in prognosis and genetic counseling.