Mesomelic Limb Shortening

► [Shortening of the middle segments of the extremities (radius and ulna; tibia and fibula)]

The most common form of mesomelic dwarfism is X-linked dominant dyschondrosteosis (Leri-Weill syndrome, OMIM 127300), a condition manifesting in late childhood and affecting female more frequently and more severely than male subjects. Varying degrees of Madelung deformity and mild shortening of the fibula and tibia, with prominence of its medial portion, are characteristic features (Fig. 5.25a,b). Genu valgum, coxa valga, and shortening of the tubular bones in the hands and feet can be additional features (Herdman et al. 1966). Mesomelic dysplasia, Langer type (OMIM 249700) is due to homozygous deletion or point mutation of the SHOX gene, which causes dyschondrosteosis in the heterozygous state. Short limbs with mesomelic mi-cromelia and hypoplastic mandible are major clinical features. The distal portion of the ulna is hypoplastic, and the radius is short and wide with dorsolateral bowing and tilting of its end-portion towards the ulna. The hand is deviated toward the ulna. The tibia is short and wide, with metaphyseal flaring. The fibula is proximally deficient (Langer 1967). The autosomal dominant mesomelic dysplasia, Nievergelt type (OMIM 163400) is the most severe form of mesomelic dysplasia. Bones in the shanks are markedly hy-poplastic and deformed, with rhomboid or triangular configuration of the tibia. The fibula is involved to a lesser extent. Occasionally, the bones in the forearm are also affected, the radius displaying more severe shortening and widening than the ulna. Proximal ra-dioulnar synostosis and, in later years, tarsal synos-tosis are distinguishing features (Young and Wood 1975). The unique rhomboidal shape of the tibia and fibula helps differentiate this condition from recessive mesomelic dwarfism, Langer type, and from Grebe chondrodysplasia (OMIM 200700), an autosomal recessive disorder characterized by normal axial skeleton and skull and severely shortened and deformed limbs, with a proximal-distal gradient of severity (Costa et al. 1998). Mesomelic dysplasia, Werner type (OMIM 188770) is an autosomal dominant disorder with bilateral tibial hypoplasia/aplasia. The forearm is usually not affected. Absence of the thumb and polydactyly or syndactyly of the hands and feet are additional features (Pashayan et al. 1971). A lethal autosomal recessive form of the disease has been described (Kozlowski and Ekof 1987).

Ulnofibular dysplasia, Rheinhardt-Pfeiffer type (OMIM 191400), which has an autosomal dominant inheritance, is another dwarfing disorder presenting at birth with mesomelic brachymelia. There is distal shortening of the ulna, bowing of the radius, and volar dislocation of the radial head. The fibula is proximally deficient, expanded at mid-shaft, and laterally angulated, with a cutaneous dimple at the apex of the angulation (Rheinhardt and Pfeiffer 1967). Hy-poplasia of the lateral aspect of the distal tibia, with lateral tilting of the talus, is also a feature. Mild cases of the Nievergelt type of mesomelic dysplasia and Rheinhardt-Pfeiffer dysplasia may be difficult to differentiate, both clinically and radiologically. Me-somelic dwarfism, hypoplastic tibia-radius type (OMIM 156230) features bilateral hypoplasia/aplasia of the tibia and radius, elongated fibula, and shortening of the lower legs. Tibial pseudarthrosis may be seen. Additional findings include absent thumbs, polydactyly, aplasia of the patella, and varying degrees of metatarsal and phalangeal hypoplasia (Leroy 1975). Mesomelic brachymelia, with prominent involvement of the forearms, occurs in Robinow syndrome ('fetal face' syndrome, OMIM 180700). Hypoplasia of the distal ulna and dislocation of the radial head are present. Craniofacial dysmorphism (large neurocranium), genital hypoplasia, and abnormalities in the hands (clefting of the distal phalanx in the thumb, clinodactyly of the 5th finger) are additional features (Robinow et al. 1969). Severe costovertebral segmentation defects with mesomelia are distinguishing features of the autosomal recessive COVES-DEM syndrome (OMIM 268310). Acromesomelic dys-plasia Maroteaux type (OMIM 602875) is a rare autosomal recessive disorder characterized by mesomelic brachymelia and shortening of hands and feet. The involved gene(s) has(have) been mapped to 9p13-p12 (Kant et al. 1998). Affected patient are dwarves, with short distal limbs and a disproportionately large head. The radius is short and curved, the ulna is distally deficient, and the tubular bones in the hands and feet are very short, broad, and stubby. Cone-shaped epiphyses develop.A relatively large great toe, with wide proximal and distal phalanges, are occasionally seen (Langer et al. 1977). Additional features are posteriorly deficient vertebral bodies, curved clavicles, metaphyseal flaring of long tubular bones, and hypoplasia of the basilar portions of the ilia. It has been shown that the Maroteaux type and the Campailla-Martinelli type of acromesomelic dyspla-sia represent different manifestations of the same disorder (Kant et al. 1998). Severe acromelia, scapho-cephaly, and elbow contracture are more typical of

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Fig. 5.25 a, b. Upper limb brachymesomelia in a woman patient. There is shortening of the radius and ulna (radius shorter than ulna) and dorsal subluxation of dis

tal ulna, a pattern reminiscent of the Madelung deformity. However, severe deficiency and dislocation of the radial head, lack of radial bowing, and absent trian-

gularization of distal radial epiphysis and carpal bones militate against Madelung deformity. The patient had no other remarkable abnormalities, and the bones in

the shanks (not shown) were normal

the Maroteaux type, whereas vertebral anomalies, scoliosis, and shortening of the 4th and 5th metatarsals and 2nd and 3rd phalanges are characteristic of the Campailla-Martinelli type (Kaitila et al. 1976). A similar disorder, with manifestations closely resembling those of Grebe chondrodysplasia, is referred to as acromesomelic dys-plasia, Hunter-Thompson type (OMIM 201250). Features in this type are more severe, including marked hypoplasia or aplasia of several bony elements in the hands and feet, but the axial skeleton is not involved. The Hunter-Thompson type of acromesomelic dysplasia and Grebe chondrodys-plasia are allelic disorders, caused by mutations in cartilage-derived morpho-genetic protein (CDMP1) located at 20q11.2 (Thomas et al. 1996). Heterozygous mutations in the CDMP1 gene may cause the autosomal dominant brachydactyly type C (Polin-kovsky et al. 1997). Acromesomelic brachymelia also occurs in chon-droectodermal dysplasia (Ellis-van Creveld syndrome, OMIM 225500), an autosomal recessive dwarfing disorder with hand polydactyly, hamate-capitate fusion, and heart defects (Taylor et al. 1984).

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