Dr Alan Cameron 01 January 2001
Mesomelic dysplasias are a heterogeneous group of disorders characterized by disproportionate shortening of the middle segment of the limbs. They have been reported diagnosed in the second trimester. The most frequent varieties will be reviewed in this section but there are many other rare forms whose description is beyond the scope of this text. Acromesomelic dysplasia will be discussed elsewhere. Dyschondrosteosis is an autosomal dominant disorder with mild mesomelia that becomes evident in late childhood.
The Langer type is probably homozygous for the autosomal dominant gene of dyschondrosteosis and is characterized by marked shortening of the forearms and shanks, mild mandibular hypoplasia and normal intelligence. The ulna and radius are hypoplastic and there is marked angulation of the radial shaft. The tibia is short, thickened and often angulated. There is hypoplasia or absence of ossification of the proximal half of the fibula.
The Nievergelt type is also an autosomal dominant disorder with severe involvement of the upper and lower limbs. There is marked hypoplasia of the radius and ulna with radio-ulnar synostosis seen in some cases. The fibula and tibia are also very hypoplastic with the former being longer than the latter. The tibia has a rhomboidal shape, while the fibula is often angulated. Clubfeet are commonly present.
The Robinow type has significant genetic heterogeneity and there are autosomal dominant and recessive forms. There is a characteristic facies with a triangular mouth, hypertelorism, hypoplastic external genitalia and congenital heart disease. The forearms are primarily affected with the ulna being shorter than the radius. The hands and feet are normal or small. There are multiple rib anomalies (40%), vertebral fusions and hemivertebrae (70%).
The Werner type is also autosomal dominant, although a more severe lethal autosomal recessive form has been reported. There is marked clinical and intra-familial variability. The forearm is mildly affected but the tibia is aplastic or severely hypoplastic, there is patellar aplasia or hypoplasia (70%), preaxial polydactyly of the hands (60%) and feet (99%). The fibula is hypoplastic (mild). Triphalangeal thumbs may be present. There is varying degree of shortening of the forearm and lower legs. Depending on the type, the upper or lower extremities may be more severely affected. Comparison between the long bones of the leg with the femur, and the forearm bones with the humerus will assist in the diagnosis.
There is a spectrum of abnormality of the radius, ulna, tibia and fibula that includes mild to severe shortening, bowing, and proximal or distal hypoplasia.
Bone synostosis and abnormal position of the hands can also be seen.
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