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Spondyloepiphyseal Dysplasia Congenita
Introduction
Spondyloepiphyseal dysplasias are rare, nonlethal disorders of bone growth. These disorders primarily affect the spine (spondylo-) and the ends of the long bones (epiphyseal), resulting in a short-trunk dwarfism. These disorders are clinically and genetically heterogeneous. Some spondyloepiphyseal dysplasias manifest in the prenatal period, including spondyloepiphyseal dysplasia congenita (SEDC), whereas others manifest in childhood. Other spondyloepiphyseal dysplasias are diagnosed in later life as early-onset arthropathy. This chapter focuses on the most common form that is prenatal in onset, SEDC, which results from mutations in type II collagen encoded by COL2A1 .
Disorder
Definition
SEDC is a nonlethal disorder caused by mutations in the gene that encodes type II collagen, COL2A1 . Abnormal synthesis of type II collagen, a major component of cartilage, leads to short stature, kyphoscoliosis, early-onset osteoarthritis, and hearing and vision problems.
Prevalence and Epidemiology
The exact prevalence is unknown but is one of the more common nonlethal skeletal disorders.
Etiology, Pathophysiology, and Embryology
Autosomal dominantly inherited mutations in COLA2A1, the gene that encodes for the type II collagen protein, are responsible for SEDC, and therefore both sexes are equally affected. If both parents are affected because of nonassorting mating, there is a 25% chance of homozygosity, which is generally lethal in infancy.
Type II collagen is highly expressed in certain tissues, in particular in cartilage and the vitreous of the eye, and thus affected individuals have both short stature and a high incidence of eye abnormalities. Other rare forms of spondyloepiphyseal dysplasias are inherited as autosomal recessive and X-linked disorders (spondyloepiphyseal dysplasia tarda).
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