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KEY POINTS
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Key Points

  • Refers to a group of rare, generally lethal skeletal dysplasias that have short limbs, short ribs, and polydactyly. Clinical overlap exists between the four subtypes.

  • Extremely rare in the general population.

  • Differential diagnosis includes Ellis–van Creveld syndrome, asphyxiating thoracic dystrophy (Jeune syndrome), Meckel–Gruber syndrome, and trisomy 13.

  • All affected infants with short-rib polydactyly syndrome have severe pulmonary hypoplasia that prevents extrauterine survival.

  • Chromosomes are usually normal. Genes responsible for these conditions have not yet been identified.

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CONDITION
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The short-rib polydactyly syndromes comprise a group of rare, generally lethal skeletal dysplasias. Much debate exists within the clinical genetics community as to the appropriate subclassifications, if any, for these conditions. Sonographic characteristics common to all the subtypes of the short-rib polydactyly syndromes include short horizontal ribs and long tubular bone changes that result in severe micromelia. Most of the conditions have associated polydactyly of the feet and hands. A variety of organ anomalies can also accompany this condition (de Sierra et al., 1992).

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The short-rib polydactyly syndromes (SRPS) have been divided into four types. Type I SRPS (Saldino–Noonan syndrome) was first described in 1972 (Saldino and Noonan, 1972). It is characterized by extremely short bones with pointed and narrowed metaphyses. The ribs are also extremely short, causing compression of the developing lungs. This eventually results in severe pulmonary hypoplasia. Saldino–Noonan syndrome is also associated with more severe systemic abnormalities than exist in some of the other subtypes. These abnormalities include congenital heart disease, anorectal anomalies, and cysts in the kidneys. Polydactyly is present in more than 95% of cases of type I SRPS (Keating et al., 1989).

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Type II SRPS (Majewski syndrome) was first described in 1971 (Majewski et al., 1971). These patients have very short ribs, severe pulmonary hypoplasia, micromelia, and polydactyly. A distinguishing feature of the syndrome is the presence of a median or midline cleft lip with or without cleft palate. These patients also have a very high frequency of central nervous system abnormalities (Lurie, 1994). The most common central nervous system abnormalities seen in Majewski syndrome include pachygyria, small cerebellar vermis, and absent olfactory bulbs (Martínez-Frías et al., 1993). Other central nervous system changes that have been demonstrated in type II SRPS include arachnoid cysts, agenesis of the corpus callosum, and arrhinencephaly (Prudlo et al., 1993). In addition to the midline cleft lip and cleft palate, patients with Majewski syndrome can have a cleft tongue, oral frenulae, natal teeth, and abnormalities of the epiglottis (Knapp et al., 1990).

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Type III SRPS (Verma–Naumoff syndrome) was first described in 1977 (Verma et al., 1975; Naumoff et al., 1977). Patients with this subtype clinically resemble patients with type I because of the absence of cleft lip. These patients have the typical long narrow thorax with ...

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