Expanding the phenotypic spectrum of ECEL1-related congenital contracture syndromes.

Using a combination of homozygosity mapping and whole-exome sequencing (WES), we identified a novel missense c.1819G>A mutation (G607S) in the endothelin-converting enzyme-like 1 (ECEL1) gene in a consanguineous pedigree of Turkish origin presenting with a syndrome of camptodactyly, scoliosis, limited knee flexion, significant refractive errors and ophthalmoplegia. ECEL1 mutations were recently reported to cause recessive forms of distal arthrogryposis. This report expands on the molecular basis and the phenotypic spectrum of ECEL1-associated congenital contracture syndromes.

Mapping a gene for congenital fibrosis of the extraocular muscles to the centromeric region of chromosome 12.

Congenital Fibrosis of the Extraocular Muscles (CFEOM) is an autosomal dominant, ocular disorder characterized by congenital, nonprogressive, bilateral ptosis and external ophthalmoplegia. The pathophysiology of this disorder is unknown and it is unclear if it has a primary neurogenic or myopathic etiology. We report linkage of this disorder, in two unrelated families, to markers in the pericentromeric region of human chromosome 12. D12S59 does not recombine with the disease giving a two-point lod score of 12.5 (theta = 0.00). D12S87 and D12S85 flank the CFEOM locus with two-point lod scores of 8.9 (theta = 0.03) and 5.4 (theta = 0.03) respectively, defining a region of 8 cM. These data establish a map location for CFEOM and demonstrate that this may be a genetically homogeneous disorder.

Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2.

Isolated strabismus affects 1-5% of the general population. Most forms of strabismus are multifactorial in origin; although there is probably an inherited component, the genetics of these disorders remain unclear. The congenital fibrosis syndromes (CFS) represent a subset of monogenic isolated strabismic disorders that are characterized by restrictive ophthalmoplegia, and include congenital fibrosis of the extraocular muscles (CFEOM) and Duane syndrome (DURS). Neuropathologic studies indicate that these disorders may result from the maldevelopment of the oculomotor (nIII), trochlear (nIV) and abducens (nVI) cranial nerve nuclei. To date, five CFS loci have been mapped (FEOM1, FEOM2, FEOM3, DURS1 and DURS2), but no genes have been identified. Here, we report three mutations in ARIX (also known as PHOX2A) in four CFEOM2 pedigrees. ARIX encodes a homeodomain transcription factor protein previously shown to be required for nIII/nIV development in mouse and zebrafish. Two of the mutations are predicted to disrupt splicing, whereas the third alters an amino acid within the conserved brachyury-like domain. These findings confirm the hypothesis that CFEOM2 results from the abnormal development of nIII/nIV (ref. 7) and emphasize a critical role for ARIX in the development of these midbrain motor nuclei.

Horizontal gaze palsy with progressive scoliosis can result from compound heterozygous mutations in ROBO3.

BACKGROUND: Horizontal gaze palsy with progressive scoliosis (HGPPS) is an autosomal recessive disorder characterised by congenital absence of horizontal gaze, progressive scoliosis, and failure of the corticospinal and somatosensory axon tracts to decussate in the medulla. We previously reported that HGPPS patients from consanguineous pedigrees harbour homozygous mutations in the axon guidance molecule ROBO3. METHODS: We now report two sporadic HGPPS children of non-consanguineous parents who harbour compound heterozygous mutations in ROBO3. The mother of one of the children also had scoliosis DNA was extracted from a blood sample from each participant using a standard protocol, and the coding exons of ROBO3 were amplified and sequenced as previously described. RESULTS: Each patient harboured two unique heterozygous mutations in ROBO3, having inherited one mutation from each parent. CONCLUSIONS: HGPPS can result from compound heterozygous mutations. More comprehensive examinations of parents and siblings of HGPPS patients are required to determine if the incidence of scoliosis in individuals harbouring heterozygous ROBO3 mutations is greater than in the general population.

A Japanese family with FEOM1-linked congenital fibrosis of the extraocular muscles type 1 associated with spinal canal stenosis and refinement of the FEOM1 critical region.

We identified a Japanese family with congenital fibrosis of the extraocular muscles, including 24 affected individuals through five generations. To determine their form of congenital fibrosis of the extraocular muscles, we performed clinical and linkage studies. DNA typing for linkage to the FEOM1 (12p11.2-q12) and FEOM3 (16qter) loci was performed on genomic DNA, using fluorescent microsatellite polymorphic markers. All affected individuals shared the common manifestations of congenital fibrosis of the extraocular muscles type 1 including congenital ptosis, infraducted globe position in primary gaze, and upward gaze palsy in both eyes. Unexpectedly, we found apparent spinal canal stenosis in the cervical spine in all affected family members who were examined. Genetic analysis revealed linkage to the FEOM1 locus with a maximum lod score of 4.42 at theta of zero. One affected family member harbored a recombination event between D12S345 and D12S1692, narrowing the FEOM1 locus from the published 3-cM region flanked by D12S1584 and D12S1668 to a 2.1-cM region flanked by D12S345 and D12S1668. Thus, we have established that this family segregates congenital fibrosis of the extraocular muscles type 1 as an autosomal dominant trait and that their disorder both maps to and refines the FEOM1 locus. This is the first clinical and genetic report of such a family in the Japanese population and the first report of spinal involvement in congenital fibrosis of the extraocular muscles.

CFEOM3: a new extraocular congenital fibrosis syndrome that maps to 16q24.2-q24.3.

PURPOSE: To define the clinical characteristics and determine the gene localization for a previously undescribed form of congenital fibrosis of the extraocular muscles (CFEOM), referred to as CFEOM type 3 (CFEOM3). METHODS: A large family with CFEOM was identified, and participating individuals underwent ophthalmologic examination and donated blood for genetic analysis. The family's disorder was tested for linkage to the known CFEOM loci, followed by a genome-wide search and linkage refinement using polymorphic DNA markers. RESULTS: Thirty-eight members of this Canadian family participated in the study. Affected individuals are born with a nonprogressive eye movement disorder characterized by variable expression of ptosis and restrictive external ophthalmoplegia. Severely affected individuals have ptosis, primary gaze fixed in a hypo- and exotropic position, and marked restriction of eye movement bilaterally. Mildly affected individuals have normally positioned globes with a limitation of vertical gaze. Moderately affected individuals have asymmetrical involvement with one eye severely and one eye mildly affected. The disorder is autosomal dominant with variable expression and probable incomplete penetrance. Genetic analysis reveals linkage to markers on 16q24.2q24.3. A maximum lod score of 5.8 occurs at markers D16S3063 and D16S689, and the CFEOM3 disease gene is located within a 5.6-cM region flanked by D16S486 and D16S671. CONCLUSIONS: These data establish that CFEOM3 is a phenotypically variant and genotypically distinct form of CFEOM with linkage to chromosome 16qter. The authors have previously demonstrated that CFEOM1 results from a developmental absence of the superior division of the oculomotor nerve. The authors hypothesize that CFEOM3 results from a defect analogous to, but distinct from CFEOM1.

A clinically variant fibrosis syndrome in a Turkish family maps to the CFEOM1 locus on chromosome 12.

OBJECTIVES: To describe the phenotype of a Turkish family with variably expressed congenital fibrosis of the extraocular muscles (CFEOM), and to determine the genetic location of their disorder. METHODS: Participants were examined and had blood extracted for genetic analysis. The clinical features of the family's disorder were studied, and the disorder was tested for linkage to the 3 known CFEOM loci (CFEOM1, CFEOM2, and CFEOM3). RESULTS: Twenty-nine affected and 31 unaffected family members participated in the study. Eighteen affected individuals had congenital bilateral ptosis and restrictive infraductive (downward) ophthalmoplegia, consistent with the published descriptions of classic CFEOM families linked to the CFEOM1 locus. Eleven affected individuals, however, had eye(s) in a neutral primary position, residual upgaze, and/or absence of ptosis, thus deviating from previous descriptions of CFEOM1-linked families. Analysis of the autosomal dominant variably expressed disorder in this family revealed linkage to the CFEOM1 locus on chromosome 12 with a maximum lod score of 10.8 at D12S85. CONCLUSIONS: This Turkish family segregates a variably expressed form of CFEOM that most closely resembles CFEOM3-linked CFEOM, but maps to the CFEOM1 locus. CLINICAL RELEVANCE: These data establish that there is much greater phenotypic heterogeneity at the CFEOM1 locus than previously reported, and this may blur our ability to distinguish the different CFEOM loci based solely on clinical presentation. Arch Ophthalmol. 2000;118:1090-1097

Analysis of human sarcospan as a candidate gene for CFEOM1.

BACKGROUND: Congenital fibrosis of the extraocular muscles type 1 (CFEOM1) is an autosomal dominant eye movement disorder linked to the pericentromere of chromosome 12 (12p11.2 - q12). Sarcospan is a member of the dystrophin associated protein complex in skeletal and extraocular muscle and maps to human chromosome 12p11.2. Mutations in the genes encoding each of the other components of the skeletal muscle sarcospan-sarcoglycan complex (alpha - delta sarcoglycan) have been shown to cause limb girdle muscular dystrophy (LGMD2C-F). To determine whether mutations in the sarcospan gene are responsible for CFEOM1 we: (1) attempted to map sarcospan to the CFEOM1 critical region; (2) developed a genomic primer set to directly sequence the sarcospan gene in CFEOM1 patients; and (3) generated an anti-sarcospan antibody to examine extraocular muscle biopsies from CFEOM1 patients. RESULTS: When tested by polymerase chain reaction, sarcospan sequence was not detected on yeast or bacterial artificial chromosomes from the CFEOM1 critical region. Sequencing of the sarcospan gene in CFEOM1 patients from 6 families revealed no mutations. Immunohistochemical studies of CFEOM1 extraocular muscles showed normal levels of sarcospan at the membrane. Finally, sarcospan was electronically mapped to bacterial artificial chromosomes that are considered to be outside of the CFEOM1 critical region. CONCLUSIONS: In this report we evaluate sarcospan as a candidate gene for CFEOM1. We have found that it is highly unlikely that sarcospan is involved in the pathogenesis of this disease. As of yet no sarcospan gene mutations have been found to cause muscular abnormalities.

Evidence of genetic heterogeneity in autosomal recessive congenital fibrosis of the extraocular muscles.

PURPOSE: Autosomal recessive congenital fibrosis of the extraocular muscles (CFEOM2) has been described in families from Saudi Arabia. Affected individuals have ptosis and exotropic ophthalmoplegia, and their disease has been mapped to chromosome 11q13. Here, we describe the phenotypic findings in a similarly affected Yemenite family and analyze the family for linkage to the CFEOM2 locus, as well as to the autosomal dominant CFEOM1 and CFEOM3 loci on chromosomes 12cen and 16q24, respectively. METHODS: The family was ascertained through two affected daughters. There are four unaffected siblings, and the parents are consanguineous. Each family member was examined, and linkage analysis was performed using markers from the CFEOM1, CFEOM2, and CFEOM3 loci. RESULTS: Both affected daughters have congenital bilateral ophthalmoplegia. The 15-month-old proband has restrictive exotropia. She fixates with either eye in abduction and with a compensatory head turn to the opposite side. Her 4-year-old sister has a small exotropia and severely limited eye movements. All other family members have normal ophthalmologic examinations. Genetic analysis excluded linkage of the family's disease to the CFEOM2 and CFEOM3 loci. A lod score of 2.0 (the maximum possible, given the family size and structure), was obtained at the CFEOM1 locus, and the alleles reduced to homozygosity in both affected daughters and none of the other children. CONCLUSIONS: These data establish that there is genetic heterogeneity in autosomal recessive CFEOM and suggest that this second recessive locus may be allelic to the autosomal dominant CFEOM1 locus at 12cen.

Clinical characterization of the HOXA1 syndrome BSAS variant.

BACKGROUND: The Bosley-Salih-Alorainy syndrome (BSAS) variant of the congenital human HOXA1 syndrome results from autosomal recessive truncating HOXA1 mutations. We describe the currently recognized spectrum of ocular motility, inner ear malformations, cerebrovascular anomalies, and cognitive function. METHODS: We examined nine affected individuals from five consanguineous Saudi Arabian families, all of whom harbored the same I75-I76insG homozygous mutation in the HOXA1 gene. Patients underwent complete neurologic, neuro-ophthalmologic, orthoptic, and neuropsychological examinations. Six individuals had CT, and six had MRI of the head. RESULTS: All nine individuals had bilateral Duane retraction syndrome (DRS) type 3, but extent of abduction and adduction varied between eyes and individuals. Eight patients were deaf with the common cavity deformity of the inner ear, while one patient had normal hearing and skull base development. Six had delayed motor milestones, and two had cognitive and behavioral abnormalities meeting Diagnostic and Statistical Manual of Mental Disorders-IV criteria for autism spectrum disorder. MRI of the orbits, extraocular muscles, brainstem, and supratentorial brain appeared normal. All six appropriately studied patients had cerebrovascular malformations ranging from unilateral internal carotid artery hypoplasia to bilateral agenesis. CONCLUSIONS: This report extends the Bosley-Salih-Alorainy syndrome phenotype and documents the clinical variability resulting from identical HOXA1 mutations within an isolated ethnic population. Similarities between this syndrome and thalidomide embryopathy suggest that the teratogenic effects of early thalidomide exposure in humans may be due to interaction with the HOX cascade.

Diffusion tensor MRI shows abnormal brainstem crossing fibers associated with ROBO3 mutations.

Horizontal gaze palsy with progressive scoliosis (HGPPS) is caused by mutations in the ROBO3 gene, critical for the crossing of long ascending medial lemniscal and descending corticospinal tracts in the medulla. Diffusion tensor imaging in a patient with HGGPS revealed the absence of major pontine crossing fiber tracts and no decussation of the superior cerebellar peduncles. Mutations in the ROBO3 gene lead to a widespread lack of crossing fibers throughout the brainstem.

Differential effects of antibiotics inhibiting gyrase.

Both oxolinic acid and coumermycin A1, inhibitors of DNA gyrase, block DNA synthesis in Escherichia coli. At low concentrations of oxolinic acid, the rate of bacterial DNA synthesis first declines rapidly but then gradually increases. This gradual increase in synthesis rate depended on the presence of wild-type recA and lexA genes; mutations in either gene blocked the increase in synthesis rate. In such mutants, oxolinic acid caused a rapid decline, followed by a slow, further decrease in DNA synthesis rate. Coumermycin A1, however, produced a more gradual decline in synthesis rate which is unaffected by defects in the recA or lexA genes. An additional difference between the two drugs was observed in a dnaA mutant, in which initiation of replication is temperature sensitive. Low concentrations of oxolinic acid, but not coumermycin A1, reduced thermal inhibition of DNA synthesis rate.

DNA gyrase on the bacterial chromosome: possibility of two levels of action.

In previous studies we have shown that oxolinic acid, a specific inhibitor of the A subunit of DNA gyrase, induces DNA cleavage at 100,000-base-pair intervals on the Escherichia coli chromosome. At subsaturating drug concentrations, cleavage is induced at a fraction of these sites and DNA synthesis is partially inhibited. This partial inhibition is surprisingly rapid even when few sites have been inactivated. We now report kinetic measurements suggesting that inactivation of 100,000-base-pair gyrase sites by oxolinic acid does not inhibit DNA synthesis by simply producing barriers to replication fork movement. Slowing the rate of fork movement, thus increasing the time for a fork to reach a barrier, fails to proportionately slow inhibition of DNA synthesis. Moreover, the initial, rapid phase of inhibition is followed by a slower decline that is not accelerated by increasing the frequency of barriers by raising drug concentrations. These data, when added to the observation that additional oxolinic acid-induced cleavage occurs in replicating regions of the chromosome, suggest that gyrase may function at replication forks as well as at 100,000-base-pair intervals on the chromosome.

Mutilating hand syndrome in an infant with familial carpal tunnel syndrome.

A 7-month-old infant, son of consanguinous Indian parents, presented with recurrent chewing of his digits in a median nerve distribution as the primary manifestation of carpal tunnel syndrome, in conjunction with features consistent with congenital insensitivity to pain. Electromyography (EMG) demonstrated severe median nerve entrapment at the wrist bilaterally, but other nerves were normal. In spite of clinical evidence of diffuse pain insensitivity, sural nerve and skin biopsies were normal, and he had no evidence of autonomic dysfunction. Hand findings evolved with scarring and infection of median innervated digits and loss of fine motor skills. Carpal tunnel release resulted in complete clinical resolution and significant EMG improvement. Milder symptoms and EMG evidence of median nerve entrapment were demonstrated in both parents, paternal grandparents, and several of his father's siblings. We hypothesize this child may be homozygous for a mutant allele that in its heterozygous state predisposes to familial autosomal dominant carpal tunnel syndrome. Homozygosity for this or another mutant allele may be responsible for his congenital insensitivity to pain.

Congenital fibrosis of the extraocular muscles associated with cortical dysplasia and maldevelopment of the basal ganglia.

BACKGROUND: Congenital fibrosis of the extraocular muscles (CFEOM) is a rare condition that has been traditionally regarded as a primary eye muscle disease. Recent studies, however, suggest that CFEOM may be the result of a primary neuropathy with secondary myopathic changes. PURPOSE: To describe a previously unrecognized association between congenital fibrosis of the extraocular muscles and structural abnormalities of the brain. DESIGN: Small case series. METHODS: Detailed clinical examinations and neuroradiologic studies were performed on the three affected family members. In addition, genetic analysis of the family was performed. RESULTS: The three affected family members, mother and two children, have the ocular features of 'classic' congenital fibrosis of the extraocular muscles. All showed dilation of the left lateral ventricle secondary to hypoplasia of the body and tail of the ipsilateral caudate nucleus. There was fusion of an enlarged caudate nucleus head with the underlying putamen. Both children showed widespread bilateral cortical dysplasia. Genetic analysis of the family was inconclusive but consistent with linkage to the CFEOM1 locus on chromosome 12. Chromosomal analysis of the affected individuals did not show evidence of a deletion of chromosome 12 and haplotype analysis was not suggestive of a microdeletion. CONCLUSIONS: Cerebral cortical and basal ganglia maldevelopment can be found in individuals with CFEOM. This suggests that neuroimaging should be considered in the initial diagnostic evaluation of these patients, particularly if there is developmental delay.

A gene for isolated congenital ptosis maps to a 3-cM region within 1p32-p34.1.

Hereditary isolated congenital ptosis is an autosomal dominant disorder with incomplete penetrance characterized by a variable degree of unilateral or bilateral drooping of the upper eyelids. We report linkage of this disorder in a large family to markers on chromosome 1p. In our sample of 37 meioses, nine informative markers did not recombine with the disease. D1S2677 gave a maximum two-point LOD score of 8.8 on the assumption of 90% penetrance (theta = 0). D1S447/2733 and D1S1616 flank the disease locus, with two-point LOD scores of 5.6/6.6 (theta = .04) and 4.9 (theta = .05), respectively, defining a region of 2.8 cM. FISH of YACs containing flanking recombinant markers localizes the gene to chromosome 1p32-p34.1. These data establish a map location for an isolated congenital ptosis gene and demonstrate that this disorder is genetically distinct from other extraocular muscle-specific disorders such as congenital fibrosis of the extraocular muscles and blepharophimosis.

Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles.

Congenital fibrosis of the extraocular muscles is an autosomal dominant congenital disorder characterized by bilateral ptosis, restrictive external ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position, and markedly limited and aberrant residual eye movements. It has been generally thought that these clinical abnormalities result from myopathic fibrosis of the extraocular muscles. We describe the intracranial and orbital pathology of 1 and the muscle pathology of 2 other affected members of a family with chromosome 12-linked congenital fibrosis of the extraocular muscles. There is an absence of the superior division of the oculomotor nerve and its corresponding alpha motor neurons, and abnormalities of the levator palpebrae superioris and rectus superior (the muscles innervated by the superior division of the oculomotor nerve). In addition, increased numbers of internal nuclei and central mitochondrial clumping are found in other extraocular muscles, suggesting that the muscle pathology extends beyond the muscles innervated by the superior division of cranial nerve III. This report presents evidence that congenital fibrosis of the extraocular muscles results from an abnormality in the development of the extraocular muscle lower motor neuron system.

Congenital fibrosis of the extraocular muscles (autosomal dominant congenital external ophthalmoplegia): genetic homogeneity, linkage refinement, and physical mapping on chromosome 12.

Congenital fibrosis of the extraocular muscles (CFEOM) is an autosomal dominant syndrome of congenital external ophthalmoplegia and bilateral ptosis. We previously reported linkage of this disorder in two unrelated families to an 8-cM region near the centromere of human chromosome 12. We now present refinement of linkage in the original two families, linkage analysis of five additional families, and a physical map of the critical region for the CFEOM gene. In each of the seven families the disease gene is linked to the pericentromeric region of chromosome 12. D12S345, D12S59, D12S331, and D12S1048 do not recombine with the disease gene and have combined lod scores of 35.7, 35.6, 16.0, and 31.4, respectively. AFM136xf6 and AFMb320wd9 flank the CFEOM locus, defining a critical region of 3 cM spanning the centromere of chromosome 12. These data support the concept that this may be a genetically homogeneous disorder. We also describe the generation of a YAC contig encompassing the critical region of the CFEOM locus. This interval has been assigned cytogenetically to 12p11.2-q12 and spans the centromere of chromosome 12. These results provide the basis for further molecular analyses of the structure and organization of the CFEOM locus and will help in the identification of candidate genes.