Physical Examination. Measurements of head circumference, height, weight, and arm span are taken, and body proportions are evaluated. A careful examination should be done for nonosseous signs such as cleft palate, cataracts, or congenital heart disease that may contribute to the diagnosis. Ophthalmologic examination and evaluation of speech and hearing may also be needed.
Intelligence is normal in nearly all types of dwarfism. Exceptions include, but are not limited to, hypochondroplasia (see Plate 4-5), the rare Dyggve-Melchior-Clausen dysplasia (see Plate 4-16), pycnodysostosis (see Plate 4-13), and Hurler and Hunter syndromes (see Plate 4-18). The need for specific intellectual evaluation or treatment is dictated by the diagnosis and the patient’s past performance.
Radiographic Findings. Radiographs must be taken of the entire skeleton (skeletal survey) because diagnosis of most bone dysplasias cannot be made on the basis of one or two radiographs of selected body parts. It is particularly important to look for atlantoaxial instability of the cervical spine. Abnormal vertebral movements occur in many bone dysplasias and, unless detected, may lead to acute compressive myelopathy. Because the radiographic characteristics of many dysplasias change with time, review of earlier radiographs is often necessary (e.g., in the epiphyseal dysplasias, the growth plates fuse with age and all evidence of disturbed epiphyseal development is obliterated).
Laboratory Tests. Initial symptoms or the preliminary diagnosis may suggest the need for specific laboratory tests. For example, if Schmid-type metaphyseal chondrodysplasia (see Plate 4-3) is suggested, a complete blood analysis is needed to differentiate this disorder from vitamin D–resistant rickets; and if the mucopolysaccharidoses, a group of biomechanical storage disorders, are suggested, testing for specific enzymes is required.
Achondroplasia, which occurs in about 1 in 40,000 persons, is the most common and best-known type of disproportionate short-limb dwarfism (see Plates 4-1 to 4-3). It is transmitted by a single autosomal dominant gene. Infants with homozygous achondroplasia generally do not survive for more than a few weeks or months. About 80% of cases result from a spontaneous mutation. The mutation occurs in the fibroblast growth factor receptor 3 (FGFR-3), which affects endochondral bone formation specifically in the proliferative zone of the physis. Achondroplasia is a quantitative, not qualitative, cartilage defect. The parents are usually average size, and no other family member is affected. Statistical evidence suggests that elevated paternal age (>37 years) may be linked to this type of mutation.
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