Robinow Syndrome, Autosomal Recessive 1

A number sign (#) is used with this entry because of evidence that autosomal recessive Robinow syndrome-1 (RRS1) is caused by homozygous or compound heterozygous mutations in the ROR2 gene (602337) on chromosome 9q22.

Autosomal dominant brachydactyly type B1 (BDB1; 113000) is an allelic disorder.

Description

Autosomal recessive Robinow syndrome-1 is a severe skeletal dysplasia characterized by dysmorphic facial features, including frontal bossing, hypertelorism, and broad nose, short-limbed dwarfism, vertebral segmentation, and genital hypoplasia (summary by van Bokhoven et al., 2000).

Genetic Heterogeneity of Robinow Syndrome

Autosomal recessive Robinow syndrome-2 (RRS2; 618529) is caused by mutation in the NXN gene (612895) on chromosome 17p13.

See also autosomal dominant Robinow syndrome-1 (DRS1; 180700), caused by mutation in the WNT5A gene (164975) on chromosome 3p; DRS2 (616331), caused by mutation in the DVL1 gene (601365) on chromosome 1p36; and DRS3 (616894), caused by mutation in the DVL3 gene (601368) on chromosome 3q27.

Clinical Features

A recessive form of Robinow syndrome was suggested by the reports of Wadia (1978, 1979) and Wadlington et al. (1973). Features common in both the dominant (180700) and recessive forms are the characteristic facial features, orodental abnormalities, and hypoplastic genitalia. Bain et al. (1986) suggested that the main discriminating feature is the occurrence of multiple rib and vertebral anomalies in the recessive form. Robinow (1987) suggested that the term COVESDEM syndrome be removed from the literature to avoid confusion of terminology. He suggested that the cases so designated represent a recessive form of Robinow syndrome.

Glaser et al. (1989) described Robinow syndrome in a child of a consanguineous Turkish couple. In addition to the 'fetal face' and mesomelic dwarfism of Robinow syndrome, the infant showed severe abnormalities of the vertebral column. Glaser et al. (1989) suggested that such changes in the vertebral column are particularly characteristic of the recessive form of Robinow syndrome. In 2 sibships related as first cousins and both with consanguineous parents, Teebi (1990) observed the features of autosomal recessive Robinow syndrome: short stature, mesomelic and acromelic brachymelia, characteristic face with hypertelorism, wide palpebral fissures, midface hypoplasia and large mouth, and hypogenitalism. Nazer et al. (1990) reported 2 children, offspring of first-cousin Saudi parents, with the 'fetal face syndrome.' Both of the children also had the Crigler-Najjar syndrome, as did 2 previously born sibs who did not have the fetal face syndrome. Schorderet et al. (1992) described a brother and sister with Robinow syndrome in a Kurdish family from Turkey. The daughter had short stature, macrocephaly, hypertelorism, hepatosplenomegaly, short forearms, and marked vertebral anomalies. Her brother had hypertelorism, hypertrophied alveolar ridges, hepatosplenomegaly, short forearms, a rib anomaly, and ambiguous genitalia. The brother was mosaic for a Y-chromosome abnormality.

Balci et al. (1991) reported 14 patients, all but 1 of whom were the offspring of consanguineous marriages, and Robinow (1991) quoted Baxova of Bratislava, Czechoslovakia, as suggesting that the condition is not rare in Czechoslovakia, where all cases occurred in the offspring of consanguineous gypsy parents (see Baxova et al., 1989). Robinow (1991) also had reports of recessive cases from Saudi Arabia and Kuwait. In addition, he pointed out that some cases thought to be of the dominant variety are probably cases of omodysplasia of Maroteaux (164745), including the 2 patients reported by Bain et al. (1986).

Balci et al. (1998) described a 14-year-old girl in whom the diagnosis of Robinow syndrome had been made at the age of 2 months by Balci et al. (1993) on the basis of fetal face, gingival hyperplasia, mesomelic shortness, hemivertebrae between T10 and L2 with scoliosis, and an extra hypoplastic right middle finger. Intravenous pyelogram showed calyectasia. At the age of 14 years, she had a history of recurrent severe abdominal pain for the previous 6 months. She had not yet experienced menarche. Hematocolpos related to vaginal atresia was discovered. She underwent vaginoplasty with cervical construction. Vaginal atresia with cervical agenesis had apparently not been observed previously in Robinow syndrome. This was thought to represent a recessive form of Robinow syndrome.

Aksit et al. (1997) reported 4 unrelated cases of Robinow syndrome, all with cardinal features of the condition, including vertebral and costal anomalies. In addition, 1 patient showed extensive webbing of the toes and an epigastric hernia. In 2 cases there was parental consanguinity. Sabry et al. (1997) reported 2 unrelated consanguineous families with Robinow syndrome. In a child of a Kuwaiti family, they reported associated intrauterine growth retardation; laxity of ligaments, joints, and skin; severe normocytic anemia; and repeated infection associated with increased total T cells and an increased CD4:CD8 ratio. In a child of a Pakistani family, there was associated congenital heart disease with right atrial isomerism, atrial and ventricular septal defects, double outlet right ventricle, and pulmonary stenosis.

Soliman et al. (1998) outlined the characteristics of recessive Robinow syndrome as follows: short stature, mesomelic and acromelic brachymelia, thick, abnormally modeled radius and ulna, characteristic face (with hypertelorism, wide palpebral fissures, broad-based nose, everted nares), large mouth, gum hypertrophy with irregular and crowded teeth, costovertebral anomalies, and micropenis in males. Endocrine dysfunction has also been observed. All children with the syndrome have been found to have empty sella. There is also partial insensitivity of Leydig cells to human chorionic gonadotropin (see 118860), low basal testosterone in prepubertal boys, and a defective sex-steroid feedback mechanism (Soliman et al., 1998).

Aksit et al. (1997) noted that of the 80 cases of Robinow syndrome reported to that time, 19 were born to Turkish couples, as were the 4 cases they reported.

Mazzeu et al. (2007) reported detailed clinical features of 37 and 51 patients with recessive and dominant Robinow syndrome, respectively. More than 75% of patients with either form had hypertelorism, large nasal bridge, short, upturned nose, midface hypoplasia, mesomelic limb shortening, brachydactyly, clinodactyly, micropenis, and short stature. Hemivertebrae and scoliosis were present in more than 75% of patients with the recessive form, but in less than 25% with the dominant form. Umbilical hernia (32%) and supernumerary teeth (10%) were found exclusively in patients with the dominant form.

Beiraghi et al. (2011) compared the craniofacial and intraoral phenotypes of 9 patients with dominant Robinow syndrome to 3 patients with recessive Robinow syndrome. Although there was overlap, particularly with regard to the most prevalent features such as hypertelorism, short, wide nose, and anteverted naries, the craniofacial dysmorphology was more severe in patients with the recessive disorder. In contrast, intraoral features were more severe in patients with the dominant disorder, and included wide retromolar ridge, alveolar ridge deformation, malocclusion, gingival enlargement, dental crowding, and hypodontia. In both types, facial characteristics became less pronounced in older individuals. Beiraghi et al. (2011) suggested that the differential diagnosis may be enhanced by noting differences in the alveolar ridge deformation pattern and severity of other intraoral characteristics.

Mapping

Afzal et al. (2000) performed homozygosity mapping (also known as autozygosity mapping) in 5 consanguineous Omani families segregating autosomal recessive Robinow syndrome. Two additional affected families, 1 from Brazil and 1 from the U.K., were used to test for genetic heterogeneity and to refine the position of the locus. The results indicated that the locus, designated RBNW1, lies within a 4-cM region between markers D9S1836 and D9S1803 (maximum multipoint lod score = 12.3). The 2 non-Omani families demonstrated no evidence of genetic heterogeneity.

Molecular Genetics

Afzal et al. (2000) reported homozygous missense mutations in both intracellular and extracellular domains of ROR2 (602337) in affected individuals from 3 unrelated consanguineous families, and a nonsense mutation (602337.0004) that removed the tyrosine kinase domain and all subsequent 3-prime regions of the gene in 14 patients from 7 families from Oman. The nature of these mutations suggested that the autosomal recessive form of Robinow syndrome is caused by loss of ROR2 activity.

Simultaneously and independently, van Bokhoven et al. (2000) studied 11 families, 10 of which were derived from Turkey where autosomal recessive Robinow syndrome is unusually frequent, and 1 from Pakistan. The parents of all except one of the families were consanguineous, and for the most part first cousins. The authors mapped the gene for this disorder to 9q21-q22. They demonstrated mutations in the ROR2 gene resulting in premature stop codons and predicted nonfunctional proteins. The characteristic abnormal morphogenesis of the face and external genitalia along with short-limbed dwarfism and vertebral segmentation anomalies were emphasized as clinical features by van Bokhoven et al. (2000). A remarkable finding of van Bokhoven et al. (2000) was the fact that among the 10 families of Turkish descent, 4 homozygous nonsense mutations were detected in 6, including W720X (602337.0006) and R205X (602337.0007) (in 3 families). The families originated from different regions of Turkey, namely from the Black Sea coast (for the W720X mutation), eastern Turkey (for the 3 families with R205X) and central Turkey.

Tufan et al. (2005) described 2 adult patients with autosomal recessive Robinow syndrome. In a 28-year-old Turkish man, born of first-cousin parents, Tufan et al. (2005) identified homozygosity for a deletion (602337.0010) in the ROR2 gene. The patient had 4 unaffected sibs and 1 sib with cleft palate who died of unknown cause in infancy. Besides typical skeletal and facial features, the patient developed hydronephrosis, nephrocalcinosis, and renal failure. In a 40-year-old German man with characteristic skeletal manifestations including severe spinal involvement and endocrinologic abnormalities including elevated gonadotropic hormones, Tufan et al. (2005) identified compound heterozygosity for a missense and a nonsense mutation in the ROR2 gene (see 602337.0005). The patient's nonconsanguineous parents were heterozygous for the mutations, respectively; he had 3 unaffected sibs. Tufan et al. (2005) noted that the facial phenotype in both patients remained distinctive into adulthood.

In 2 sib pairs with Robinow syndrome from the same extended family, Brunetti-Pierri et al. (2008) identified homozygosity for deletion of exons 6 and 7 of the ROR2 gene (602337.0012). All 4 unaffected parents were heterozygous for the deletion. The patients demonstrated intrafamilial variability with respect to cleft lip, cleft palate, and cardiac abnormalities. One of the sibs presented at age 17 with back pain, and spine MRI revealed a thoracic syringomyelia; the authors noted that syringomyelia had not previously been reported in Robinow syndrome.

Genotype/Phenotype Correlations

Recessive Robinow Syndrome with Severe Malformations of the Hands and Feet

In a large Turkish kindred in which many members over at least 6 generations had dominant BDB1, Schwabe et al. (2000) described a man, born of consanguineous parents with BDB1, who was homozygous for a 5-bp deletion proximal to the TK domain in the ROR2 gene, resulting in frameshift at the arg441 residue (602337.0008). His phenotype resembled an extreme form of brachydactyly, with extensive aplasia/hypoplasia of the phalanges and metacarpals/metatarsals and absence of nails. In addition, he had vertebral anomalies, brachymelia anomalies (short arms), and a ventricular septal defect--features reminiscent of Robinow syndrome. The phenotype in this patient suggested a specific mutation effect that cannot be explained by simple haploinsufficiency and that is distinct from that in Robinow syndrome.

Schwarzer et al. (2009) reported an R441X mutation in the ROR2 gene (602337.0014) in an Omani patient exhibiting features of Robinow syndrome in conjunction with complex, symmetric brachy-syn-polydactyly of the hands and oligodactyly of the feet with absent toes 2 to 4. The Omani parents were healthy, had no features of Robinow syndrome or BDB1, and were distantly related by mothers of the same tribal background. The R441X mutation was located at the same position as the frameshift mutation at arg441. Transfection experiments with a series of mutant transcripts revealed that recessive Robinow syndrome mutant proteins, such as Q502X and W720X (602337.0006), were less abundant and retained intracellularly, whereas BDB1 mutants, such as W749X, were stable and predominantly located at the cell membrane. Both the frameshift mutation and the R441X mutation showed an intermediate pattern with membrane localization but also high ER retention, although the R441X mutant had a significantly lower total protein level and less membrane-associated protein than the frameshift mutant. There was a correlation between the severity of BDB1, the location of the mutation, and the amount of membrane-associated ROR2. Membrane protein fraction quantification revealed a gradient of distribution and stability correlating with the clinical phenotypes. This gradual model was confirmed by crossing mouse models for RRS and BDB1, yielding double heterozygous animals that exhibited an intermediate phenotype. Schwarzer et al. (2009) proposed a model in which the phenotypic outcome of ROR2 mutations is determined by 2 threshold levels: the degree of protein retention/degradation determines the RRS phenotype, whereas the amount of mutant protein reaching the plasma membrane determines the severity of the BDB1 phenotype. A mixture of both effects can result in a balance of gain of function and loss of function and, consequently, an overlapping phenotype.

Animal Model

Schwabe et al. (2004) analyzed Ror2 -/- mice as a model for the developmental pathology of Robinow syndrome. They demonstrated that vertebral malformations in the mutant mice were due to reductions in the presomitic mesoderm and defects in somitogenesis. Mesomelic limb shortening in the mice was a consequence of perturbed chondrocyte differentiation. The craniofacial phenotype was caused by a midline outgrowth defect. Ror2 expression in the genital tubercle and its reduced size in Ror2 -/- mice suggested that Ror2 is involved in genital development. Schwabe et al. (2004) concluded that ROR2 is essential at multiple sites during development and that the Ror2 -/- mouse provides a suitable model for the study of the underlying developmental malformations in individuals with Robinow syndrome.