The gene is not present on Y chromosomes and in normal females resides on and functions to inactivate many of the genes located on its own maternal but not the fathers X chromosome. Turner syndrome females with (46,X,i(Xq) sSMC consisting of a partial X chromosome that does not contain the XIST gene express at least some of this sSMCs genetic material and therefore contain excesses of this material. In consequence, they have a more serious form of the Turner syndrome that ranges form moderately severe to extremely severe. The extremely severe cases have anencephaly (absence of a major portion of the brain, skull, and scalp), agenesis of the corpus callosum (lack of the thick tract of nerve fibers that connect the left and right cerebral hemispheres), and complex heart deformities. Individuals with Turner syndrome that have partial X chromosome containing(46,X,i(Xq) sSMCs that have the XIST gene do not express this sSMCs genetic material and do not have the more severe manifestations of the syndrome. Inheritance
In the majority of cases where monosomy occurs, the X chromosome comes from the mother. This may be due to a nondisjunction in the father. Meiotic errors that lead to the production of X with p arm deletions or abnormal Y chromosomes are also mostly found in the father. Isochromosome X or ring chromosome X on the other hand are formed equally often by both parents. Overall, the functional X chromosome usually comes from the mother.
Mosaicism affects height in Turner syndrome; a large population sample drawn from the UK Biobank found women with 45,X0 karyotypes to have an average height of 145 cm (4 ft 9 in), while those with 45,X0/46,XX karyotypes averaged 159 cm (5 ft 2+1⁄2 in). The strength of the association between Turner syndrome and short stature is such that idiopathic short stature alone is a major diagnostic indication.Growth delay in Turner syndrome does not begin at birth; most neonates with the condition have a birth weight in the lower end of the normal range. Height begins to lag in toddlerhood, with a delayed growth velocity becoming apparent as early as 18 months. When girls with Turner syndrome begin school, their height is usually still not remarkably unusual; marked short stature becomes obvious in mid-childhood. In undiagnosed preadolescents and adolescents, growth delay may be mistaken for a side effect of delayed puberty and improperly treated. Short stature in Turner syndrome and its counterpoint, tall stature in sex chromosome polysomy conditions such as Klinefelter syndrome, XYY syndrome, and trisomy X, is caused by the short-stature homeobox gene on the X and Y chromosomes. The absence of a copy of the SHOX gene in Turners inhibits skeletal growth, resulting both in overall short stature and in a distinctive pattern of skeletal malformations including micrognathia (small chin), cubitus valgus (abnormal forearm angles), and short fingers.When Turner syndrome is diagnosed in early life, growth hormone therapy can decrease the degree of short stature.