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KEY POINTS
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Key Points

  • Distinct skeletal dysplasia characterized by disproportionate short stature, clubfoot, cleft palate, “hitch-hiker’s thumb,” and “cauliflower ear.”

  • Results from mutation in the diastrophic dysplasia sulfate transporter gene, DTDST (also known as SLC26A2).

  • More common in individuals of Finnish ancestry due to a founder effect.

  • Sonographic findings are short and curved limbs, micrognathia, clubfeet, abducted and proximally inserted thumbs and great toes, and normal ossification.

  • Associated with normal intelligence and postnatal development.

  • Autosomal recessive condition.

  • Delivery should occur in a tertiary center due to the high incidence of associated airway problems.

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CONDITION
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Diastrophic dysplasia is a distinct clinical entity characterized by disproportionate short stature, cleft palate, clubfoot, progressive scoliosis, limited joint mobility, proximally placed first metacarpals (“hitch-hiker’s thumb”), and cystic degeneration of the pinnae of the ear (“cauliflower deformity”) (Figure 93-1) (Lachman et al., 1981). This condition was first described by Lamy and Maroteaux (1960), who used the Greek word diastrophos, meaning twisted, to describe the prominent involvement of the feet and spine in this type of dwarfism (Diab et al., 1994).

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Figure 93-1

(Left) Postnatal photograph of a 19-week fetus with diastrophic dysplasia, illustrating severe micromelia, bilateral clubfeet, micrognathia, and bilateral hitch-hiker thumbs. (Right) Close-up of extreme lateral displacement of thumbs. (Courtesy of Dr. Joseph Semple.)

Graphic Jump Location
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Diastrophic dysplasia exhibits distinctive histopathology, which consists of cytoplasmic accumulation of glycogen and fat in the chondrocytes, resulting in variability of chondrocyte size, shape, and viability (Diab et al., 1994). There is nonuniformity of the cartilage matrix with fibroblast and vascular ingrowth, resulting in fibrotic foci and areas of intracartilaginous calcification (Diab et al., 1994). The abnormalities of the cartilage matrix are considered pathognomonic and are visible with light microscopy. The underlying problem is an excessive amount of collagen deposition within the cartilage matrix rather than a lack of collagen. The excessive deposition of structurally abnormal collagen occurs predominantly in the growth cartilage rather than the resting carti-lage (Shapiro, 1992). This cartilage abnormality affects the entire epiphyseal area, which leads not only to shortening of the long bones, but also to extreme malformation of the epiphyseal ends of the bones. This abnormality affects the articular surfaces, causing precocious osteoarthritis (Shapiro, 1992).

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The underlying genetic basis of diastrophic dysplasia is the result of a mutation in a novel sulfate transporter gene, known as the diastrophic dysplasia sulfate transporter (DTDST) and also, more recently, as SLC26A2 (Hästbacka et al., 1994, 1996). Impaired function of this gene product leads to undersulfation of proteoglycans in cartilage matrix, which leads to abnormal cartilage formation and results in the disease phenotype (Hästbacka et al., 1994).

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INCIDENCE
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Diastrophic dysplasia has been observed ...

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