Turner Syndrome : How Is It Made Up?

Turner syndrome is a well defined sex chromosomal disorder characterized by short stature, characteristic somatic stigmata, and gonadal dysgenesis. In this review, I summarize recent progress in the clarification of genetic mechanisms involved in the development of clinical features. The essence is as follows: (1) Short stature is primarily ascribed to loss of SHOX cloned from the short arm pseudoautosomal region and GCY postulated between DYZ3 and DYS11 in the proximal part of Yq, in addition to non-specific growth disadvantage caused by chromosome imbalance. (2) Skeletal features such as short matacarpals, cubitus valgus, Madelung deformity, high arched palate, and short neck are primarily attributable to SHOX haploinsufficiency, with expressivity in the limb and faciocervical regions being influenced by gonadal function status and the presence or absence of the lymphogenic gene, respectively. (3) Soft tissue features such as webbed neck and lymphedema and visceral features such as aortic coarctation and horseshoe kidney appear to be due to haploinsufficiency of the lymphogenic gene postulated between DMD and MAOA in the proximal Xp region and between PABY and DYS255 in the distal Yp region. (4) Gonadal dysgenesis is explained by pairing failure of homologous chromosomes in meiocytes that are genetically destined to develop as oocytes, rather than by the dosage effect of an X-linked gene(s). In addition, the underlying factors for the extreme prenatal lethality, cognitive dysfunction, mental retardation, gonadal tumors, and immune-related diseases are discussed.