Mesomelic dwarfism, Langer type
Langer mesomelic dysplasia (LMD) is characterized by severe disproportionate short stature with mesomelic and rhizomelic shortening of the upper and lower limbs.Prevalence is unknown but less than 70 cases have been reported in the literature so far.LMD represents a more severe form of Léri-Weill dyschondrosteosis (LWD; see this term) with severely shortened long bones of the limbs (involving both the middle and proximal segments), deformity of the humeral head, angulation of the radial shaft, carpal distortion, a short femoral neck, and absence or hypoplasia of the proximal half of the fibula. Mild hypoplasia of the mandible has been reported in some cases. In contrast to LWD, Madelung deformity (see this term) is not typically present in LMD. Associated malformations are rare and intellect is normal in almost all reported LMD cases.LMD is inherited in a pseudoautosomal recessive manner and is associated with homozygous or compound heterozygous mutations and deletions of the Short stature HomeobOX (SHOX) gene (which maps to the pseudoautosomal region 1 (PAR1) of the sex chromosomes; Xp22.33 and Yp11.32) or of the downstream PAR1 (where SHOX enhancer elements are located). LMD is part of a spectrum of disorders (ranging from the most severe, LMD, to LWD, isolated Madelung deformity and so-called idiopathic short stature; see these terms), all associated with SHOX/PAR1 anomalies. The prevalence of SHOX/PAR1 mutations is estimated at 1/1000.Diagnosis of LMD may be suspected on the basis of the clinical and radiologic findings and can be confirmed by molecular analysis (microsatellite analysis, FISH or, preferably, MLPA for PAR1 deletions, high resolution melting (HRM), dHPLC and/or DNA sequencing for point mutations, small deletions and insertions of SHOX).LMD may also be suspected by ultrasound at 20 weeks of gestation and at this stage should be differentiated from femur-fibula-ulna (FFU) complex and the Reinhardt-Pfeiffer form of mesomelic dysplasia (see these terms).Prenatal genetic testing is available; however, requests for testing for these disorders are uncommon but are more frequent for LMD.Genetic counseling should be proposed and families should be informed that SHOX/PAR1 anomalies are inherited in a pseudoautosomal dominant manner. Each child of an individual with LWD has a 50% chance of inheriting the mutation. If both parents have LWD, the offspring have a 50% chance of having LWD, a 25% chance of having LMD, and a 25% chance of having neither condition. All children of an individual with LMD and an unaffected parent will present with LWD.There is no effective treatment for LMD. The symptomatic medical management of children with LMD begins at birth and continues into adulthood. Careful monitoring of height, weight, and head circumference is essential.The short stature and limb deformities are severe but life expectancy is normal.