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KEY POINTS
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Key Points

  • Most common form of short-limbed dwarfism.

  • Incidence is 1 in 26,000 livebirths.

  • Most consistent sonographic finding is shortening of long bones between 21 and 27 weeks. Additional findings include macrocrania, frontal bossing, trident-shaped hand.

  • Differential diagnosis includes diastrophic dysplasia, achondrogenesis, Ellis–van Creveld syndrome, hypochondroplasia.

  • Condition is due to mutations in fibroblast growth factor receptor 3 (FGFR3) gene, which is a negative regulator of chondrocyte proliferation. Mutations activate the receptor and cause gain of function.

  • Pregnant women affected by achondroplasia need baseline pulmonary function tests and cesarean section delivery.

  • Prenatal diagnosis can be performed by sonography or by DNA analysis.

  • Major pediatric complications include short stature, foramen magnum compression, hydrocephalus, spinal stenosis, restrictive pulmonary disease, hypotonia, and recurrent ear infections. IQ is normal.

  • Inherited as an autosomal dominant condition, but 80% of cases are new mutations that always derive from the father and are associated with advanced paternal age.

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CONDITION
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Achondroplasia is the most common form of short-limbed dwarfism. The condition has been recognized since ancient times. Dwarfs were accepted socially in ancient Egypt, and their daily activities, recorded through art, suggest not only assimilation into daily life, but also in some cases, a high-ranking position in society (Kozma, 2006). The term achondroplasia, meaning total absence of cartilage, was first used by Parrot in 1878 (Scott, 1976). Although this is not correct in a pathologic sense, the designation is commonly accepted.

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INCIDENCE
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The incidence of achondroplasia is 1 in 26,000 livebirths (Oberklaid et al., 1979). Earlier studies that indicated an incidence of as high as 1 in 10,000 births probably included other causes of short-limbed dwarfism. More than 80% of cases are due to newmutations (Shiang et al., 1994). Advanced paternal age was initially thought to be correlated with an increased incidence of new mutations resulting in achondroplasia (Murdoch et al., 1970). However, more recent observations have led to the alternative theory that sperms bearing the fibroblast growth factor receptor 3 (FGFR3) mutation that causes achondroplasia have a selective advantage over sperms without this mutation (Horton et al., 2007).

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SONOGRAPHIC FINDINGS
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Virtually all of the bones in the body are affected by achondroplasia. Postnatal radiographic studies of the lumbar spine, pelvis, and cranial regions permit definitive diagnosis (Figure 89-1). Antenatally, diagnosis is complicated by a relatively normal appearance until the early second trimester. The most consistent sonographic finding is shortening of the long bones, particularly the femur, occurring between 21 and 27 weeks of gestation (Figure 89-2) (Kurtz et al., 1986). The overall shape of the femurs is within normal limits. Initially, a normal relationship of biparietal diameter to femur is present, but these measurements become progressively asynchronous over time (Filly et al., 1981). Additional findings that have been ...

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