Turner Syndrome and Xp Deletions: Clinical and Molecular Studies in 47 Patients

Although clinical features of Turner syndrome have primarily been explained by the dosage effects of SHOX (short stature homeobox-containing gene) and the putative lymphogenic gene together with chromosomal effects leading to nonspecific features, several matters remain to be determined, including modifying factors for the effects of SHOX haploinsufficiency, chromosomal location of the lymphogenic gene, and genetic factors for miscellaneous features such as multiple pigmented nevi. To clarify such unresolved issues, we examined clinical findings in 47 patients with molecularly defined Xp deletion chromosomes accompanied by the breakpoints on Xp21-22 (group 1; n = 19), those accompanied by the breakpoints on Xp11 (group 2; n = 16), i(Xq) or idic(X)(p11) chromosomes (group 3; n = 8), and interstitial Xp deletion chromosomes (group 4; n = 4). The deletion size of each patient was determined by fluorescence in situ hybridization and microsatellite analyses for 38 Xp loci including SHOX, which was deleted in groups 1-3 and preserved in group 4. The mean GH-untreated adult height was -2.2 SD in group 1 and -2.7 SD in group 2 (GH-untreated adult heights were scanty in group 3). The prevalence of spontaneous breast development in patients aged 12.8 yr or more (mean +/- 2 SD for B2 stage) was 11 of 11 in group 1, 7 of 12 in group 2, and 1 of 7 in group 3. The prevalence of wrist abnormality suggestive of Madelung deformity was 8 of 18 in group 1 and 2 of 23 in groups 2 and 3, and 9 of 18 in patients with spontaneous puberty and 1 of 23 in those without spontaneous puberty. The prevalence of short neck was 1 of 19 in group 1 and 7 of 24 in groups 2 and 3. Soft tissue and visceral anomalies were absent in group 1 preserving the region proximal to Duchenne muscular dystrophy and were often present in groups 2 and 3 missing the region distal to monoamine oxidase A (MAOA). Multiple pigmented nevi were observed in groups 1-3, with the prevalence of 0 of 7 in patients less than 10 yr of age and 15 of 36 in those 10 yr or older regardless of the presence or absence of spontaneous puberty. Turner phenotype was absent in group 4, including a fetus aborted at 21 wk gestation who preserved the region distal to MAOA. The results provide further support for the idea that clinical features in X chromosome aberrations are primarily explained by haploinsufficiency of SHOX and the lymphogenic gene and by the extent of chromosome imbalance in mitotic cells and pairing failure in meiotic cells. Furthermore, it is suggested that 1) expressivity of SHOX haploinsufficiency in the limb and faciocervical regions is primarily influenced by gonadal function status and the presence or absence of the lymphogenic gene, respectively; 2) the lymphogenic gene for soft tissue and visceral stigmata is located between Duchenne muscular dystrophy and MAOA; and 3) multiple pigmented nevi may primarily be ascribed to cooperation between a hitherto unknown genetic factor and an age-dependent factor other than gonadal E.