Disorders for Which Defects Are Poorly Understood or Unknown

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Chapter 691 Disorders for Which Defects Are Poorly Understood or Unknown

There are many chondrodysplasias, or chondrodysplasia clinical phenotypes, for which the genetic cause or basic mechanism is poorly understood or not known. Many illustrate features not found in other disorders and have historical significance in the evolution of chondrodysplasia nomenclature and classification.

Ellis–Van Creveld Syndrome

The Ellis-van Creveld syndrome (OMIM 225500), also known as chondroectodermal dysplasia, is a skeletal and an ectodermal dysplasia. The skeletal dysplasia presents at birth with short limbs, especially the middle and distal segments, accompanied by postaxial polydactyly of the hands and sometimes of the feet. Nail dysplasia and dental anomalies (including neonatal, absent, and premature loss of teeth and upper lip defects) constitute the ectodermal dysplasia. Common manifestations also include atrial septal defects and other congenital heart defects.

Skeletal radiographs reveal short tubular bones with clubbed ends, especially the proximal tibia and ulna (Fig. 691-1). Carpal bones display extra ossification centers and fusion; cone-shaped epiphyses are evident in the hands. A bony spur is often noted above the medial aspect of the acetabulum.

Ellis-van Creveld syndrome is an autosomal recessive trait that occurs most often in the Amish. Mutations have been identified in one of two genes, EVC (EVC1) and EVC2, which map in a head-to-head configuration to chromosome 4p. The functions of the gene products are unknown. About 30% of patients die of cardiac or respiratory problems during infancy. Life span is otherwise normal; adult heights range from 119 to 161 cm.

Cartilage-Hair Hypoplasia

Cartilage-hair hypoplasia (CHH) (OMIM 250250) is also known as metaphyseal chondrodysplasia—McKusick type. It is recognized during the 2nd year because of growth deficiency affecting the limbs, accompanied by flaring of the lower rib cage, a prominent sternum, and bowing of the legs. The hands and feet are short, and the fingers are very short with extreme ligamentous laxity. The hair is thin, sparse, and light colored, and nails are hypoplastic. The skin is hypopigmented.

Radiographs show short tubular bones with flared, irregularly mineralized, and cupped metaphyses (Fig. 691-2). The knees are more affected than are the hips, and the fibula is disproportionately longer than the tibia. The metacarpals and phalanges are short and broad. Spinal radiographs reveal mild platyspondyly.

Nonskeletal manifestations associated with CHH include immunodeficiency (T-cell abnormalities, neutropenia, leukopenia, and susceptibility to chickenpox; children also may have complications from smallpox and polio vaccinations), malabsorption, celiac disease, and Hirschsprung disease. Adults are at risk for malignancy, especially non-Hodgkin lymphoma and skin tumors. Adults reach heights of 107-157 cm.

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