Homozygous or compound heterozygous mutations as well as biallelic deletions of SHOX and/or the enhancer regions result in a more severe phenotype, which is known as Langer Mesomelic Dysplasia (LMD; MIM #249700).
Caused by mutations in the homeobox gene SHOX, its varied clinical manifestations include isolated short stature, Léri-Weill dyschondrosteosis, and Langer mesomelic dysplasia.
Deletions in the SHOX gene are the most frequent genetic cause of Leri-Weill syndrome and Langer mesomelic dysplasia, which are also present in idiopathic short stature.
Genetic alterations in SHOX result in two skeletal dysplasias; Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia (LMD), while no human genetic disease has been linked to date with SHOX2.
Molecular defects of LWD/LMD include various microdeletions in PAR1 that involve exons and/or the putative upstream or downstream enhancer regions of SHOX, as well as several intragenic mutations.
Here, we report on a consanguineous family with a novel deletion downstream of SHOX in which homozygously deleted individuals have a phenotype intermediate between Léri-Weill dyschondrosteosis and Langer Mesomelic dysplasia while heterozygously deleted individuals are mostly asymptomatic.
In 14 of these 17 patients, this was the only potentially causative abnormality detected (13 had symptoms consistent with LWD and one had short stature only), but the other three 47.5 kb deletions were found in patients with an additional causative SHOX mutation (with symptoms of LWD rather than LMD).
Since most patients with LMD with deletions downstream of SHOX gene also have SHOX mutations in trans, it may suggest these deletions are associated with a milder phenotype.
Heterozygous mutations of SHOX have been implicated in patients with Madelung's deformity, Leri-Weill dyschondrosteosis (77%), Turner's syndrome (66%), and idiopathic short stature (3%), and homozygous mutations of SHOX gene have been identified in patients with Langer's mesomelic dysplasia (100%).
Haploinsufficiency of the SHOX gene causes short stature with highly variable clinical severity, ranging from isolated short stature without dysmorphic features to Léri-Weill syndrome, and with no functional copy of the SHOX gene, Langer syndrome.
The LMD proband described here represents the first LMD case due to compound heterozygosity for deletions of the two different PAR1 regions, SHOX-encompassing and downstream from SHOX, that have been shown to be implicated in the pathogenesis of LWD and LMD.
Deficiencies or mutations in the human pseudoautosomal SHOX gene are associated with a series of short-stature conditions, including Turner syndrome, Leri-Weill dyschondrosteosis, and Langer mesomelic dysplasia.
Here, we report on a microdeletion in the SHOX 3' region identified in a Japanese infant with LMD-compatible skeletal features and a 45,X[191]/46,X,r(X)(p22.3q24)[9] karyotype and in her mother with LWDC-compatible skeletal features and a normal 46,XX karyotype.
SHOX mutations resulting in SHOX haploinsufficiency have been found in LWD and in a variable proportion of patients with idiopathic short stature (ISS), whereas homozygous loss of SHOX results in the more severe Langer mesomelic dysplasia (LMD).
Functional analysis of a missense mutation R173C (C517T) affecting the identified SHOX-NLS in two families with LWS and LD showed that the mutated SHOX protein is unable to enter the nucleus.
The results, in conjunction with the previous findings, suggest that mesomelic skeletal features such as Langer mesomelic dysplasia and LWDC, which are absent or rare in Turner syndrome, are primarily caused by the SHOX dosage effect and the bone maturing effect of gonadal estrogens, whereas other skeletal features such as short metacarpals, cubitus valgus, and various craniofacial and cervical skeletal stigmata, which are common in Turner syndrome, are largely contributed by a compressive effect of distended lymphatics and lymphedema on the developing skeletal tissues.
Although originally described as causing idiopathic short stature, SHOX mutations are also responsible for mesomelic growth retardation and Madelung deformity in Léri-Weill dyschondrosteosis and Langer mesomelic dysplasia.