► [Hypoplasia or aplasia involving the ulna, the carpals located on the ulnar side (pisiform and hamate, rarely triquetrum and capitate), and the 4th and 5 th fingers]
Ulnar ray deficiency is considerably less common than radial ray deficiency. This holds true for both aplasia and hypoplasia of the ulnar ray. The defect is most often isolated and sporadic (Birch-Jensen 1949),but when associated with other malformations it can be inherited as a mendelian trait. Just like radial defects, ulnar deficiencies can be uni- or bilaterally distributed and can range in severity from mild hypoplasia of the 4th and 5th digits to complete absence of the ulna, ulnar digits, and carpals bound to the ulna (Fig. 6.17). In very mild cases only the distal phalanx of the 5th digit is hypoplastic. Occasionally, the metacarpal of the 5th digit is lacking, so that the proximal 5th phalanx arises from the 4th metacarpal. Partial aplasia of the ulna occurs when only the proximal part of the ulna is ossified at birth and the re-
mainder of the bone is absent. A fibrocartilaginous band occasionally extends from the ossified proximal portion to the carpus or distal radial epiphysis, causing radial bowing, ulnar deviation of the hand and wrist, and/or dislocation of the radial head. Humeroradial synostosis is an occasional feature. Deficiency of the ulna is often associated with varying degrees of shortening of the forearm. Not uncommonly, the fibula and shank are also hypoplastic, and in these cases the term 'mesomelic limb shortening' is appropriate.
In this section some rare disorders are presented in which deficiency of the ulnar ray is an important component of the phenotypic spectrum. Conditions with a limb defect affecting the ulnar ray almost exclusively are discussed first, followed by disorders with combined ulnar and fibular ray defects, and then by disorders with ulnar, fibular, and femoral defects. The situations in which ulnar-ray deficiency is associated with central digit defects are discussed in the next section.
Isolated ulnar hypoplasia (OMIM 191440) with severe radial bowing but no other skeletal abnormalities has been described in a father and daughter (Fryns et al. 1988). Postaxial acrofacial dysostosis (Miller syndrome,OMIM 263750) is an association of ulnar ray deficiency, cup-shaped ears, and malar hy-poplasia (Miller et al. 1979). Micrognathia and cleft lip and palate are additional features. The limb defect consists most typically in the uni- or bilateral absence of the 5th digit and toe, often in association with hypoplasia of the ulna (Donnai et al. 1987). Autosomal recessive inheritance is likely. Similarities with Treacher-Collins syndrome (OMIM 154500) are recognized. The postaxial deficiency in the limbs distinguishes the disorder from Nager syndrome (OMIM 154400), in which limb deficiency is preaxial. Bilateral hypoplasia of the ulnas, with mesomelic shortness of the upper limbs, occurs in association with mental retardation, clubfeet, and absence of finger- and toenails in the condition referred to as ulnar hypoplasia with mental retardation (OMIM 276821), probably an autosomal recessive (Kohn et al. 1995). The ulnar-mammary syndrome (Schinzel syndrome, OMIM 181450) is a familial disorder in which defects of the ulnar rays and fibular rays are associated with delayed puberty, hypogenitalism, obesity, and hypoplasia of the nipples and apocrine glands. Occasional manifestations include anal atresia, pyloric stenosis, inguinal hernias, laryngeal stenosis, ventricular sep-tal defect, and dental abnormalities (Schinzel 1987). The upper limb malformation varies from hypopla-sia of the terminal phalanx of the 5th finger to complete absence of the ulna and of fingers 4 and 5. The defect is often bilateral but not symmetrical. Stiffness of the 5th finger is a consistent finding. Evidence has emerged to suggest that this syndrome is identical to the ulnar-mammary syndrome of Pallister (Pallister et al. 1976) and may be the same entity as 'split hand with aplasia of the ulna syndrome' (Franceschini et al. 1992). The disease is caused by mutation in the TBX3 gene on 12q23-q24.1. Interestingly, mutations in the closely linked and structurally related TBX5 gene cause preaxial limb anomalies in Holt-Oram syndrome (OMIM 142900) in association with cardiac anomalies (Bamshad et al. 1997). Phenotypic overlap with the limb-mammary syndrome (OMIM 603543) is recognized. Weyers ulnar ray/oligodactyly syndrome (OMIM 602418) is an autosomal dominant disorder with variable penetrance and expressivity, which manifests variable ulnar and fibular ray defects with oligodactyly, a single central incisor, and anomalies involving the kidneys, the spleen, and the heart (Weyers 1957). Atelosteogenesis type II (de la Chapelle syndrome, OMIM 256050) and fibuloulnar aplasia or hypoplasia with renal abnormalities (OMIM 228940), a lethal acrorenal developmental complex with ulnar hypoplasia, fibular aplasia, oligosyndactyly, and micrognathia (Saito et al. 1989), are similar to Weyers ulnar ray/oligodactyly syndrome. (This disorder must not be confused with Weyers acrodental dysostosis, a condition with postaxial polydactyly, anomalies involving the lower jaw, dentition, and oral vestibule and allelic to Ellis van Creveld syndrome.) Distal ulnar hypoplasia and bowed radius are associated with hypoplasia of the proximal fibula and distal tibia in the autosomal dominant ulnofibular dysplasia, Rheinhardt-Pfeiffer type (OMIM 191400) (Pfeiffer 1966; Reinhardt and Pfeiffer 1967). It is possible that this disorder is allelic to dyschondrosteosis (OMIM 127300). As discussed elsewhere, overlap is recognized between Rheinhardt-Pfeiffer dysplasia and mild cases of the Nievergelt type of mesomelic dysplasia. Longitudinal deficiency of the ulnar ray can occur in association with defects of the fibula and femur in the femur-fibula-ulna syndrome (FFU complex, OMIM 228200). Amelia, peromelia at the lower end of the humerus, and humeroradial synostosis are additional features that can be present in the upper extremities of patients with FFU complex (Kuhne et al. 1967). Another recognized association, sharing similarities not only with the FFU syndrome but also with Fuhrmann syndrome (OMIM 228930) and Al-Awadi/Raas-Roth-schild syndrome (OMIM 276820), is that of aplasia/ hypoplasia of the pelvis, femur, fibula, and ulna with abnormal digits and nails (OMIM 601849) (Kumar et al. 1997).
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