Opitz-Kaveggia Syndrome

A number sign (#) is used with this entry because of evidence that the Opitz-Kaveggia syndrome, also known as FG syndrome-1 (FGS1), is caused by mutation in the MED12 gene (300188) on chromosome Xq13.

Description

Opitz-Kaveggia syndrome (OKS) is an X-linked recessive mental retardation syndrome characterized by dysmorphic features, including relative macrocephaly, hypertelorism, downslanted palpebral fissures, prominent forehead with frontal hair upsweep, and broad thumbs and halluces. Most have hypotonia, constipation, and partial agenesis of the corpus callosum. Some patients have sensorineural hearing loss and joint laxity evolving into joint contractures. Affected individuals tend to be hyperactive and talkative (summary by Graham et al., 1999).

In their original family, Opitz and Kaveggia (1974) named the disorder 'FG syndrome' according to the Opitz system of using initials of patients' surnames.

Genetic Heterogeneity of FG Syndrome

Other forms of 'FG syndrome' were characterized due to the similar clinical features observed by Opitz and Kaveggia (1974). FGS2 (300321) is caused by mutation in the FLNA gene (300017) on chromosome Xq28 and FGS4 (300422) is caused by mutation in the CASK gene (300172) on chromosome Xp11. FGS3 (300406) has been mapped to Xp22.3, and FGS5 (300581) to Xq22.3.

Risheg et al. (2007) suggested that the designation Opitz-Kaveggia syndrome be reserved for those cases with mutation in the MED12 gene. In part this is justified by the fact that a MED12 mutation was found in the family originally reported by Opitz and Kaveggia (1974).

See also Lujan-Fryns syndrome (309520), an allelic disorder with an overlapping phenotype.

Clinical Features

Opitz and Kaveggia (1974) described 3 brothers and 2 of their male first cousins who were affected with mental retardation, disproportionately large head, imperforate anus, and congenital hypotonia. Partial agenesis of the corpus callosum was proved in one and suspected in a second. The authors considered this disorder to be distinct from that reported by Menkes et al. (1964); see 304100.

Riccardi et al. (1977) reported another affected male in the original family and 3 affected brothers from an unrelated family. To the preceding features they added short stature, hypotonia, joint contractures, seizures, strikingly characteristic personality and facies, gastrointestinal defects besides imperforate anus, and congenital heart defects. Riccardi et al. (1977) concluded that the family of Keller et al. (1976) had the same condition. In a nonconsanguineous family, Keller et al. (1976) observed 3 brothers with an apparently 'new' syndrome manifested by mental retardation, short stature, frontal upsweep of the hair, laterally displaced inner canthi, small simplified ears, and broad great toes. Three additional brothers died in infancy from what was thought to be a similar pattern of abnormality. Two of these had imperforate anus and died in the first days of life. The third was thought to have ventricular septal defect and had anteriorly displaced stenotic anal opening with megacolon. One of the living affected brothers had anterior displacement of the anus. The authors favored X-linked inheritance, in part because the mother showed lateral displacement of the inner canthi and anterior displacement of the anus.

The brain findings at autopsy in an 18-year-old male were reported by Opitz et al. (1982). The occurrence of 2 or 3 affected sons from each of 3 sisters in the original FG family confirmed X-linked inheritance. The mother of the patients reported by Keller et al. (1976) showed telecanthus, hypertelorism, and anteriorly displaced anus, but was of normal intelligence. The syndrome 'at birth, should be suspected in every boy with imperforate anus, and at older ages in any male with congenital hypotonic joint contractures, mental retardation, and constipation with and without functional megacolon, and in any retarded hypotonic boy with the characteristic facial appearance and personality' (Opitz et al., 1982). Neri et al. (1984) added sensorineural deafness as a feature. Imperforate anus and sensorineural deafness are associated in the Townes-Brocks syndrome (107480). Both congenital hypotonia and constipation can be severe.

Thompson et al. (1985) found probable carrier manifestations in 2 mothers and a sister of affected males. These features were broad forehead, anterior 'cowlick,' hypertelorism, long philtrum, and open mouth. Facial hypotonia resulting in downturned mouth were present in all 7 cases of Thompson et al. (1985) and all but 1 had 'cowlicks.' (See 139400.) Thompson et al. (1986) reported postmortem findings in the proband of Burn and Martin (1983). Abnormality of the cavum septi pellucidi was judged to be a forme fruste of agenesis of the corpus callosum which has been found in some cases.

Thompson and Baraitser (1987) stated that following the initial description of 5 related males by Opitz and Kaveggia (1974), 26 cases had been reported. Opitz et al. (1988) reported 5 new cases. Some patients were described as having hypo- and hyperpigmented linear streaks on the shoulders, back, and buttocks.

Thompson et al. (1989) described a family in which 4 males related through females had a mental retardation syndrome in a pattern consistent with X-linked recessive inheritance. Although the diagnosis was not clear, the FG syndrome was suggested by severe constipation, tall and broad foreheads, hypotonia, and cowlicks of the frontal hairline. None of the affected males had all features of the FG syndrome and none had macrocephaly. Fetal finger pads are typical of this disorder and of the Kabuki make-up syndrome (147920).

Kato et al. (1994) described a Japanese kindred with 3 affected males and 2 carrier females, 1 with mild clinical manifestations and 1 without. The proband was born with anal atresia and had a particular craniofacial appearance characterized by frontal cowlick, wide forehead, macrocephaly, hypertelorism, and long philtrum. CT scan showed agenesis of the corpus callosum. His thumbs and great toes were broad. Psychomotor development was delayed. An older brother had similar facial features, agenesis of the corpus callosum, broad thumb and hallux, syndactyly between the right fourth and fifth fingers, and undescended testes. He had chronically suffered from severe constipation due to anal stenosis and was mentally retarded. A younger brother of the mother of these 2 boys had the characteristic facial appearance, broad thumbs and halluces, patent ductus arteriosus (see 607411), cryptorchidism, severe constipation, and mental retardation. There was no evidence of agenesis of the corpus callosum on CT scan. The mother had frontal cowlick and broad forehead; the maternal grandmother had no abnormalities. The grandmother had given birth to another boy who died at age 10 days of respiratory failure and may have been affected.

Zwamborn-Hanssen et al. (1995) referred to the FG syndrome as a triad of mental retardation, hypotonia, and constipation. They described a family with FG syndrome in 2 males and mild features in their mother. They compared the findings in this family with those of 56 reported patients. At birth, affected individuals present with hypotonia and constipation and/or anal anomalies and joint hyperlaxity. Mental deficiency is the rule. Craniofacial dysmorphism is nonspecific. Macrocephaly may be present at birth or develop later in life. Features in older patients include joint contractures and a typically pleasant personality, sometimes with sudden aggressive outbursts, however. FG syndrome has a variable clinical presentation and clinical diagnosis is difficult, especially in sporadic patients. Thorough examination of the family with special attention to mild manifestations in female relatives may be helpful. The mother in the reported family was of normal intelligence and had no dysmorphic features. She suffered, however, from severe constipation as did her mother, the maternal grandmother.

Associated congenital hypotonia with joint hyperlaxity usually progresses to contractures with spasticity and unsteady gait in later life (Romano et al., 1994). Constipation, with or without anal anomalies, is a distinctive major finding of FG syndrome. It may not resolve until middle childhood for many patients (Romano et al., 1994).

Graham et al. (1998) described new associated findings in affected males: sagittal craniosynostosis and split-hand malformation.

Graham et al. (1999) compared behavioral and personality characteristics of 6 boys with FG syndrome to other boys with syndromic and nonsyndromic mental retardation, using standardized behavioral and personality testing methods. The boys with FG syndrome had socially oriented, attention-seeking behaviors similar to those of boys with Williams syndrome. These studies confirmed the previous descriptions of a typical personality in FG syndrome.

Rauch et al. (1998) considered the report of Chrzanowska et al. (1998), detailing a 'new' branchial syndrome that included foramina parietalia permagna, to represent a case of the FG syndrome. Chrzanowska et al. (1998) described a single sporadic case of an 11-year-old boy with symmetric parietal bone defects, triangular face, micrognathia, downslanting palpebral fissures with epicanthal folds, low-set, posteriorly angulated ears with one auricular pit, low anterior and posterior hair line, short webbed neck, bilateral asymmetric branchial cleft fistulae lateral to the sternocleidomastoid, right cryptorchidism, and hypoplastic penis with hypospadias. Multiple skeletal abnormalities included S-shaped cervical-thoracic scoliosis, malsegmentation of the upper thoracic spine, sacrococcygeal dysplasia, and bowed legs. Intelligence was normal. Rauch et al. (1998) based their position on the finding of several features described by Chrzanowska et al. (1998) in FG patients and carriers. Rauch et al. (1998) further noted that branchial arch remnants and foramina parietalia permagna were seen, respectively, in each of 2 brothers with the FG syndrome.

Smith et al. (2000) reported 4 brothers with developmental delay, minor anomalies, and symptoms due to gastrointestinal dysmotility. There was some resemblance to FG syndrome, although none of the brothers had sufficient findings to make this diagnosis. The proband presented at age 1 month with screaming episodes around meal times, mild gastroesophageal reflux, and severe constipation. Esophageal manometry studies were consistent with the diagnosis of 'nutcracker esophagus.' Symptomatic and manometric improvement followed treatment with oral calcium channel blockers and with age. Two older and less severely affected brothers had similar manometric findings but did not require treatment. A fourth brother with symptoms in infancy was found at the time of report to have normal esophageal manometry findings. A sister and their mother had no gastrointestinal symptoms. Smith et al. (2000) concluded that these brothers probably had an X-linked FG-like syndrome.

Graham et al. (2008) reported 2 new patients with FG syndrome and reviewed the cognitive and behavioral aspects of 8 other patients. All showed deficits in communication skills, particularly language development, which was associated with inattention, anxiety, and sometimes impulsive behavior. Socialization skills were comparatively better than communication skills. Graham et al. (2008) advocated an individualized approach to treating these specific disturbances, including language therapy, a highly structured environment, and psychopharmacology when appropriate.

Diagnosis

Clark et al. (2009) defined FG syndrome as an X-linked multiple congenital anomaly-cognitive impairment disorder caused by the R961W mutation in the MED12 gene (300188.0001). Clark et al. (2009) identified all known patients with this mutation to delineate their clinical phenotype and devise a clinical algorithm to facilitate molecular diagnosis. Twenty-three males with the R961W mutation in MED12 from 9 previously reported FG syndrome families and 1 new family were reported. Six patients were reviewed in detail. These 23 patients were compared with 48 MED12 mutation-negative patients who had the clinical diagnosis of FG syndrome. Traits that best discriminated between these 2 groups were chosen to develop an algorithm with high sensitivity and specificity for the R961W MED12 mutation. All affected individuals had a family history of X-linked mental retardation, deceased male infants, and/or multiple fetal losses. No females manifested any symptoms. Clinical criteria included small ears (10th percentile or less); characteristic facies, including dolichocephaly, tall forehead, frontal upsweep, long narrow face, puffy eyelids, and open mouth; and congenital anomalies of the corpus callosum, anus, heart, or skeleton in the proband or an affected male relative from the maternal lineage. Patients manifested an affable, eager-to-please personality with or without anxiety, evident by the age of 5 years, and either true macrocephaly (greater than 98th percentile) or relative macrocephaly (head circumference percentile greater than the percentile for height). Affected patients also had early hypotonia, constipation, or feeding problems severe enough to require medical intervention. Per Clark et al. (2009), exclusion criteria are female sex, normal intelligence with IQ similar to parents and unaffected sibs, affected females in the pedigree, and male-to-male inheritance in the pedigree. Clark et al. (2009) stated that this algorithm identifies the R961W MED12 mutation-positive group with 100% sensitivity and 90% specificity.

Mapping

In a linkage analysis of 10 families segregating FG syndrome, Briault et al. (1997) found linkage with DXS441 at Xq13 on 2-point analysis; maximum lod = 3.39 at theta = 0.12. In addition, separate analysis of the lod scores obtained for the Xq13 markers suggested linkage exclusion for 3 families. Genetic heterogeneity was confirmed by analysis of the linkage results with the HOMOG program.

Graham et al. (1998) described 3 additional families and corroborated the localization of an FG syndrome locus, FGS1, to Xq12-q21.

Briault et al. (1999) reported an X-chromosome inversion, inv(X)(q12q28), in a French boy with FG syndrome and in his mentally retarded maternal uncle. Using FISH in further studies of this family, Briault et al. (2000) identified 2 clones that crossed the breakpoints, one located at Xq11.2 and the other at Xq28 (FGS2; 300321).

In 3 families with FGS1, Lossi et al. (2000) excluded 9 candidate genes that map to the same general region of Xq.

X-Chromosome Inactivation

Graham et al. (1998) noted skewed X inactivation in carrier females of FGS. Raynaud et al. (2003) studied the X-inactivation profile of 45 females (obligate carriers and other family members) from 16 multiplex families segregating FGS. They found interfamilial differences of inactivation profiles, but no X-inactivation pattern correlated with specific FGS loci.

Molecular Genetics

Insights into the pathogenesis of Opitz-Kaveggia syndrome were gained in the course of evaluating candidate genes that influence thyroid function (Risheg et al., 2007). One such candidate gene, located at Xq13, is MED12 (300188), which encodes a thyroid hormone receptor-associated protein (TRAP). To examine the possible role of MED12 in X-linked mental retardation (XLMR), Risheg et al. (2007) sequenced the 45 exons of MED12 in 24 index cases from XLMR families with linkage to Xq13. Two of the 24 index cases had an identical nucleotide substitution (2881C-T; 300188.0001). Two affected individuals were both diagnosed a priori with Opitz-Kaveggia syndrome and were from different ethnic backgrounds. Subsequent analyses of other patients identified the same 2881C-T substitution in 1 additional affected male and in 2 mothers of affected sons (both deceased). Clinical analysis of the affected members of these 6 families showed relative macrocephaly (OFC percentile greater than height percentile) in 7 of 9; high, prominent forehead in 9 of 10; small, simple ears in 7 of 7; mental retardation in 9 of 9; hypotonia in 9 of 10; dysgenesis of corpus callosum in 6 of 6; wide flat thumbs and great toes in 7 of 7; congenital heart defect in 3 of 10; constipation in 5 of 8; anal anomaly in 7 of 10; and cryptorchidism in 4 of 8.

Based on linkage studies and clinical reports in the literature, coupled with their own findings, Risheg et al. (2007) concluded that individuals reported as Opitz-Kaveggia syndrome in fact are a clinically and genetically heterogeneous group representing mutations at various loci. They proposed that the Opitz-Kaveggia syndrome designation be reserved for those individuals with MED12 mutations.

Initially described as a rare multiple congenital anomaly/mental retardation syndrome occurring only in boys (Opitz and Kaveggia, 1974), FG syndrome is now recognized as a more common disorder also occurring in girls. Battaglia et al. (2006) described 25 patients from Pisa, Italy; 6 were female.