Holt-Oram syndrome (HOS) is characterized by upper-limb defects, congenital heart malformation, and cardiac conduction disease. Upper-limb malformations may be unilateral, bilateral/symmetric, or bilateral/asymmetric and can range from triphalangeal or absent thumb(s) to phocomelia. Other upper-limb malformations can include unequal arm length caused by aplasia or hypoplasia of the radius, fusion or anomalous development of the carpal and thenar bones, abnormal forearm pronation and supination, abnormal opposition of the thumb, sloping shoulders, and restriction of shoulder joint movement. An abnormal carpal bone is present in all affected individuals and may be the only evidence of disease. A congenital heart malformation is present in 75% of individuals with HOS and most commonly involves the septum. Atrial septal defect and ventricular septal defect can vary in number, size, and location. Complex congenital heart malformations can also occur in individuals with HOS. Individuals with HOS with or without a congenital heart malformation are at risk for cardiac conduction disease. While individuals may present at birth with sinus bradycardia and first-degree atrioventricular (AV) block, AV block can progress unpredictably to a higher grade including complete heart block with and without atrial fibrillation.

Osteogenesis imperfecta (OI) is a connective tissue disorder characterized by bone fragility and low bone mass. Due to considerable phenotypic variability, Sillence et al. (1979) developed a classification of OI subtypes based on clinical features and disease severity: OI type I, with blue sclerae (166200); perinatal lethal OI type II, also known as congenital OI (166210); OI type III, a progressively deforming form with normal sclerae (259420); and OI type IV, with normal sclerae (166220). Most forms of OI are autosomal dominant with mutations in one of the 2 genes that code for type I collagen alpha chains, COL1A1 (120150) and COL1A2 (120160). Glorieux et al. (2000) described a novel autosomal dominant form of OI, which they designated OI type V (OI5), in 7 patients. The disorder was similar to OI type IV but had distinctive clinical, histologic, and molecular characteristics. OI type V is characterized by calcification of the forearm interosseous membrane, radial head dislocation, a subphyseal metaphyseal radiodense line, and hyperplastic callus formation (summary by Cho et al., 2012). OI type V has a variable phenotype. For example, in patients with the more common c.-14C-T variant (614757.0001), distinctive radiographic findings (calcification of the forearm interosseous membrane, radial head dislocation, a subphyseal metaphyseal radiodense line, and hyperplastic callus formation) are often seen, whereas these findings are not seen in patients with the less common S40L variant (614757.0002).

Radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) is characterized by thrombocytopenia that progresses to pancytopenia, in association with congenital proximal fusion of the radius and ulna that results in extremely limited pronation and supination of the forearm (summary by Niihori et al., 2015). For a discussion of genetic heterogeneity of radioulnar synostosis with amegakaryocytic thrombocytopenia, see RUSAT1 (605432).

Radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) is characterized by thrombocytopenia that progresses to pancytopenia, in association with congenital proximal fusion of the radius and ulna that results in extremely limited pronation and supination of the forearm (summary by Niihori et al., 2015). Genetic Heterogeneity of Radioulnar Synostosis with Amegakaryocytic Thrombocytopenia Radioulnar synostosis with amegakaryocytic thrombocytopenia-2 (RUSAT2; 616738) is caused by heterozygous mutation in the MECOM gene (165215) on chromosome 3q26.

There are 2 types of radioulnar synostosis: in type 1, there is a proximal, smooth fusion of 2 to 6 cm between the radius and ulna and the radial head is absent; in type 2, there is a fusion just distal to the proximal radial epiphysis in association with congenital dislocation of the radial head (Bauer and Jonsson, 1988). Both types result in a limitation of pronation and supination of the forearm, and in type 2 there is also a restriction of extension at the elbow. Dominant inheritance through several lines in several generations was demonstrated by a family reported by Davenport et al. (1924). Hansen and Andersen (1970) found a positive family history in 5 of 37 cases. Radioulnar synostosis is a feature of certain chromosome abnormalities, notably the triple X-Y syndrome (XXXY). See pronation-supination of the forearm, impairment of (176800). Radioulnar synostosis occurs in an autosomal dominant syndrome with amegakaryocytic thrombocytopenia; see RUSAT1, 605432.

ROR2-related Robinow syndrome is characterized by distinctive craniofacial features, skeletal abnormalities, and other anomalies. Craniofacial features include macrocephaly, broad prominent forehead, low-set ears, ocular hypertelorism, prominent eyes, midface hypoplasia, short upturned nose with depressed nasal bridge and flared nostrils, large and triangular mouth with exposed incisors and upper gums, gum hypertrophy, misaligned teeth, ankyloglossia, and micrognathia. Skeletal abnormalities include short stature, mesomelic or acromesomelic limb shortening, hemivertebrae with fusion of thoracic vertebrae, and brachydactyly. Other common features include micropenis with or without cryptorchidism in males and reduced clitoral size and hypoplasia of the labia majora in females, renal tract abnormalities, and nail hypoplasia or dystrophy. The disorder is recognizable at birth or in early childhood.

Distal arthrogryposis type 11 (DA11) is an autosomal dominant disorder characterized mainly by camptodactyly. Other features include absent flexion creases and limited forearm supination (Zhou et al., 2019).