Mutations in FAM20C also identified in non-lethal osteosclerotic bone dysplasia

Raine syndrome is an osteosclerotic bone dysplasia, which has proved to be lethal within the first few weeks of life in all the reported cases to date. We recently identified a chromosomal rearrangement and telomeric microdeletion in a patient with Raine syndrome and subsequently identified mutations in the FAM20C gene, located within the deleted region, in six additional Raine syndrome cases. The phenotype of Raine syndrome in the cases examined was remarkably consistent with generalized osteosclerosis of all bones, periosteal bone formation, characteristic facial phenotype and lethal within the first few weeks of life. In the current study, we have identified two unrelated individuals who presented at birth with a sclerosing bone dysplasia with features very similar to those in Raine syndrome but who survived infancy and are now aged 8 and 11 years, respectively. Mutations in FAM20C, consistent with autosomal recessive inheritance, were identified in both cases. In the first case, a homozygous non-synonymous mutation in exon 7 (1309G>A D437N) was identified, and in the second case, compound heterozygosity for non-synonymous mutations in exon 2 (731T>A I244N) and in exon 3 (796G>A G266R) was revealed. Raine syndrome has been previously considered to be a neonatal lethal condition. However, the identification of mutations in these two patients confirms a broader phenotypic spectrum and that mutation of FAM20C does not always lead to the infantile lethality previously seen as a prerequisite for Raine syndrome diagnosis.

A mutation in NFkappaB interacting protein 1 causes cardiomyopathy and woolly haircoat syndrome of Poll Hereford cattle

Cardiomyopathy and woolly haircoat syndrome (CWH) of Poll Hereford cattle is a lethal, autosomal recessive disorder. Cardiac and haircoat changes are congenital, neonatal ocular keratitis develops in some cases and death usually occurs within the first 12 weeks of life. We undertook a homozygosity mapping approach to identify the chromosomal location of the causative gene. Seven candidate genes were examined for homozygosity in affected animals: desmoplakin and junction plakoglobin (both previously implicated in human cardiocutaneous syndromes), desmocollin 2, desmoglein 2, plakophilin 2, nuclear factor kappa B (NFKB1) and NFkappaB interacting protein 1 (PPP1R13L, also known as NKIP1). Homozygosity in 13 affected animals was observed at the PPP1R13L locus, located on bovine chromosome 18. Subsequent sequence analysis revealed a 7-bp duplication (c.956_962dup7) in exon 6 of this 13-exon gene. This frameshift variant is predicted to result in the substitution of three amino acids and the introduction of a premature stop codon at position 325 of the protein product (p.Ser322GlnfsX4). PPP1R13L interacts with NFkappaB, a family of structurally related transcription factors that regulate genes controlling inflammation, immune responses and cell proliferation and survival. CWH represents a large-animal model for cardiocutaneous disorders caused by a mutation in the PPP1R13L gene. The identification of this bovine mutation also indicates that PPP1R13L and other genes affecting NFkappaB activity may be candidate genes in the study of human cardiovascular disease.

A novel locus for an autosomal recessive hereditary spastic paraplegia (SPG35) maps to 16q21-q23

BACKGROUND

The hereditary spastic paraplegias (HSPs) are a group of clinically and genetically heterogeneous neurodegenerative disorders in which the cardinal pathologic feature is upper motor neuron degeneration leading to progressive spasticity and weakness of the lower limbs. To date, 14 autosomal recessive HSP loci have been mapped.

METHODS

We have identified a large consanguineous Omani family in which an autosomal recessive form of HSP is segregating. The age at onset varied from 6 to 11 years and the course of the disease is progressive with intellectual disability and is associated with seizures in two individuals. To map the chromosomal location of the causative gene we undertook 250K gene chip SNP analyses of all affected individuals assuming that a founder mutation was responsible.

RESULTS

All affected individuals shared a 20.4 Mb (3.25 cM) region of homozygosity located on chromosome 16q21-q23.1, defined by SNP markers rs149428 and rs9929635 (peak multipoint lod score of 4.86). Two candidate genes, dynein, cytoplasmic 1, light intermediate chain 2 (DYNC1LI2) and vacuolar protein sorting 4 homolog A (VPS4A), were sequenced but no disease causing mutations were identified.

CONCLUSION

We have mapped the chromosomal location of a novel gene responsible for a form of hereditary spastic paraplegia (HSP) (SPG35) and defined its clinical presentation.

Mutations in FAM20C are associated with lethal osteosclerotic bone dysplasia (Raine syndrome), highlighting a crucial molecule in bone development

The generation and homeostasis of bone tissue throughout development and maturity is controlled by the carefully balanced processes of bone formation and resorption. Disruption of this balance can give rise to a broad range of skeletal pathologies. Lethal osteosclerotic bone dysplasia (or, Raine syndrome) is an autosomal recessive disorder characterized by generalized osteosclerosis with periosteal bone formation and a distinctive facial phenotype. Affected individuals survive only days or weeks. We have identified and defined a chromosome 7 uniparental isodisomy and a 7p telomeric microdeletion in an affected subject. The extent of the deleted region at the 7p telomere was established by genotyping microsatellite markers across the telomeric region. The region is delimited by marker D7S2563 and contains five transcriptional units. Sequence analysis of FAM20C, located within the deleted region, in six additional affected subjects revealed four homozygous mutations and two compound heterozygotes. The identified mutations include four nonsynonymous base changes, all affecting evolutionarily conserved residues, and four splice-site changes that are predicted to have a detrimental effect on splicing. FAM20C is a member of the FAM20 family of secreted proteins, and its mouse orthologue (DMP4) has demonstrated calcium-binding properties; we also show by in situ hybridization its expression profile in mineralizing tissues during development. This study defines the causative role of FAM20C in this lethal osteosclerotic disorder and its crucial role in normal bone development.

The natural history of Noonan syndrome: a long-term follow-up study

OBJECTIVE

To define better the adult phenotype and natural history of Noonan syndrome.

DESIGN

A prospective observational study of a large cohort.

RESULTS

Data are presented for 112 individuals with Noonan syndrome (mean age 25.3 (range 12-71) years), who were followed up for a mean of 12.02 years. Mutations in PTPN11 were identified in 35% of probands. Ten subjects died during the study interval; three of these deaths were secondary to heart failure associated with hypertrophic cardiomyopathy. Pulmonary stenosis affected 73 (65%) subjects; 42 (58%) required no intervention, nine underwent balloon pulmonary valvuloplasty (three requiring further intervention) and 22 surgical valvuloplasty (three requiring further intervention). Hypertrophic cardiomyopathy affected 21 (19%) patients, which had remitted in two cases, but one subject required cardiac transplant. No subjects died suddenly or had symptoms suggestive of arrhythmia. The mean final adult height was 167.4 cm in males and 152.7 cm in females. Feeding problems in infancy were identified as a predictor of future outcome. The mean age of speaking in two-word phrases was 26 months for those with no feeding difficulties, compared with 39 months for those with severe problems requiring nasogastric feeding. Attendance at a school for children with special needs for the same groups was 12.5% and 58%, respectively. A statement of special educational need had been issued in 44% overall; however, academic achievement was broadly similar to that of the general population.

IMPLICATIONS

Although the morbidity for some patients with Noonan syndrome is low, early predictors of poorer outcome have been identified, which will help ascertain those most in need of intervention.

Analysis of the population structure in Oman

Knowledge of a population structure can be a unique aid in planning genetic services. In order to facilitate the development of genetic services in the Sultanate of Oman, a tribal data base has been developed. The historic records of the beginning of the 19th century were used as the basis and were updated with contemporary information. The tribal data base includes tribal names, locations, and the main 185 major tribes and their subsections. Tribal data can be used for health care planning and the development of disease-specific genetic registers if the hospital records also include the tribal name. They may also provide a useful aid in genetic screening and disease prevention programmes, as when specific mutations are found in rare diseases, it is likely that these will be found to be exclusive to specific tribes, and laboratory testing will be greatly simplified. It is likely that similar data bases could be developed elsewhere in the Middle East and in the immigrant communities in Western Europe.

Psychological profile of children with Noonan syndrome

A cohort of 48 children with Noonan syndrome, with a mean age of 9 years 10 months (SD 3y 7mo; 28 males, 20 females), was recruited from a national study. Children were assessed using the Wechsler Intelligence Scales and Test of Motor Impairment-Revised (TOMI-R). The Piers-Harris Self-evaluation Questionnaire was also completed in a subgroup of age-appropriate children. Children's parents and teachers completed the Rutter A and B scales to assess of the degree of behavioural and emotional problems respectively. Mean Full-scale IQ score was 84, and one-quarter of the participants had learning disabilities. Verbal IQ tended to be slightly lower than Performance IQ. About half of the group showed evidence of mild to moderate impairment, confirming the impression of 'clumsiness/developmental coordination disorder' on the TOMI-R. Level of self-esteem, as determined by the Piers-Harris Questionnaire, was comparable to that of a standardized population. This research has identified some characteristic psychological features in Noonan syndrome. However, a specific behavioural phenotype could not be identified.

Screening of patients with hereditary spastic paraplegia reveals seven novel mutations in the SPG4 (Spastin) gene

Hereditary spastic paraplegia (HSP) is a heterogeneous condition characterised in its pure form by progressive lower limb spasticity. Mutations in SPG4 (encoding spastin) may be responsible for up to 40% of autosomal dominant (AD) cases. A cohort of 41 mostly pure HSP patients from Britain and Austria, 30 of whom displayed AD inheritance, was screened for mutations in SPG4 by single strand conformation polymorphism (SSCP) analysis followed by sequencing of samples with mobility shifts. We identified eight SPG4 mutations in pure AD HSP patients, seven of which were novel: one missense mutation within the AAA cassette (1633G>T), two splice site mutations (1130-1G>T, 1853+2T>A) and four frameshift mutations (190_208dup19, 1259_1260delGT, 1702_1705delGAAG, 1845delG). A novel duplication in intron 11 (1538+42_45dupTATA) was also detected. We report the HUGO-approved nomenclature of these mutations as well. Furthermore, we detected a silent change (1004G>A; P293P), previously reported as a mutation, which was also present in controls. The frequency of SPG4 mutations detected in pure AD HSP was 33.3%, suggesting that screening of such patients for SPG4 mutations is worthwhile. Most patients will have unique mutations. Screening of SPG4 in apparently isolated cases of HSP may be of less value.

Growth hormone therapy in Noonan's syndrome: non-cardiomyopathic congenital heart disease does not adversely affect growth improvement

Twenty-three children with Noonan's syndrome were treated with growth hormone (GH) and followed for at least three years. The presence of cardiomyopathy was a contraindication to treatment. Height SDS and velocity increased during treatment. None of the 23 children developed hypertrophic cardiomyopathy during GH treatment. Children with any cardiac abnormality at the start of treatment did not show a reduced growth trend when compared with patients with normal hearts.

Two families with blepharophimosis/ptosis/epicanthus inversus syndrome have mutations in the putative forkhead transcription factor FOXL2

Blepharophimosis/ptosis/epicanthus inversus syndrome (BPES) is an autosomal dominant disorder that is characterized by distinctive eyelid abnormalities. Two clinical subtypes have been described in which type I, but not type II, is associated with premature ovarian failure. Both types of BPES are linked to 3q22-23, and the gene has recently been identified as the putative forkhead transcription factor FOXL2. We report mutation screening of FOXL2 in two families with this condition. The two mutations detected were frameshift mutations resulting from a small insertion or duplication within the gene. Both mutations would result in the production of novel carboxyl terminii, one terminating the predicted protein earlier than the wild type, and the other giving rise to a larger protein product, assuming these proteins or their mRNA were not degraded. Based on the present data, this would suggest that the first family should be type I and the second, type II. Although there is evidence of infertility in the first family, all 3 females in the youngest generation have normal pelvic ultrasound and hormone levels, suggesting that the divide between types I and II may not be as distinct as has been suggested.

Robinow syndrome

In 1969, Robinow and colleagues described a syndrome of mesomelic shortening, hemivertebrae, genital hypoplasia, and "fetal facies". Over 100 cases have now been reported and we have reviewed the current knowledge of the clinical and genetic features of the syndrome. The gene for the autosomal recessive form was identified as the ROR2 gene on chromosome 9q22. ROR2 is a receptor tyrosine kinase with orthologues in mouse and other species. The same gene, ROR2, has been shown to cause autosomal dominant brachydactyly B, but it is not known at present whether the autosomal dominant form of Robinow syndrome is also caused by mutations in ROR2.

Mutations in PTPN11, encoding the protein tyrosine phosphatase SHP-2, cause Noonan syndrome

Noonan syndrome (MIM 163950) is an autosomal dominant disorder characterized by dysmorphic facial features, proportionate short stature and heart disease (most commonly pulmonic stenosis and hypertrophic cardiomyopathy). Webbed neck, chest deformity, cryptorchidism, mental retardation and bleeding diatheses also are frequently associated with this disease. This syndrome is relatively common, with an estimated incidence of 1 in 1,000-2,500 live births. It has been mapped to a 5-cM region (NS1) [corrected] on chromosome 12q24.1, and genetic heterogeneity has also been documented. Here we show that missense mutations in PTPN11 (MIM 176876)-a gene encoding the nonreceptor protein tyrosine phosphatase SHP-2, which contains two Src homology 2 (SH2) domains-cause Noonan syndrome and account for more than 50% of the cases that we examined. All PTPN11 missense mutations cluster in interacting portions of the amino N-SH2 domain and the phosphotyrosine phosphatase domains, which are involved in switching the protein between its inactive and active conformations. An energetics-based structural analysis of two N-SH2 mutants indicates that in these mutants there may be a significant shift of the equilibrium favoring the active conformation. This implies that they are gain-of-function changes and that the pathogenesis of Noonan syndrome arises from excessive SHP-2 activity.

The T-box transcription factor gene TBX22 is mutated in X-linked cleft palate and ankyloglossia

Formation of the secondary palate is a complex step during craniofacial development. Disturbance of the events affecting palatogenesis results in a failure of the palate to close. As a consequence of deformity, an affected child will have problems with feeding, speech, hearing, dentition and psychological development. Cleft palate occurs frequently, affecting approximately 1 in 1,500 births; it is usually considered a sporadic occurrence resulting from an interaction between genetic and environmental factors. Although several susceptibility loci have been implicated, attempts to link genetic variation to functional effects have met with little success. Cleft palate with ankyloglossia (CPX; MIM 303400) is inherited as a semidominant X-linked disorder previously described in several large families of different ethnic origins and has been the subject of several studies that localized the causative gene to Xq21 (refs. 10-13). Here we show that CPX is caused by mutations in the gene encoding the recently described T-box transcription factor TBX22 (ref. 14). Members of the T-box gene family are known to play essential roles in early vertebrate development, especially in mesoderm specification. We demonstrate that TBX22 is a major gene determinant crucial to human palatogenesis. The spectrum of nonsense, splice-site, frameshift and missense mutations we have identified in this study indicates that the cleft phenotype results from a complete loss of TBX22 function.

Silver syndrome is not linked to any of the previously established autosomal dominant hereditary spastic paraplegia loci

The hereditary spastic paraplegias are a clinically variable and genetically heterogeneous group of disorders characterized by progressive and lower limb spasticity and weakness. Silver syndrome (SS) is a particularly disabling autosomal dominant form of the disease in which there is associated wasting of the hand muscles. In view of the fact that genes for hereditary spastic paraplegia can produce highly variable phenotypes, the eight known autosomal dominant loci were investigated for linkage to Silver syndrome. Genotyping of these loci in two large multigenerational families was incompatible with linkage to any of these regions, suggesting that an additional locus is responsible for this syndrome.

The Silver syndrome variant of hereditary spastic paraplegia maps to chromosome 11q12-q14, with evidence for genetic heterogeneity within this subtype

The hereditary spastic paraplegias (HSPs) are a complex group of neurodegenerative disorders characterized by lower-limb spasticity and weakness. Silver syndrome (SS) is a particularly disabling dominantly inherited form of HSP, complicated by amyotrophy of the hand muscles. Having excluded the multiple known HSP loci, we undertook a genomewide screen for linkage of SS in one large multigenerational family, which revealed evidence for linkage of the SS locus, which we have designated "SPG17," to chromosome 11q12-q14. Haplotype construction and analysis of recombination events permitted the minimal interval defining SPG17 to be refined to approximately 13 cM, flanked by markers D11S1765 and D11S4136. SS in a second family was not linked to SPG17, demonstrating further genetic heterogeneity in HSP, even within this clinically distinct subtype.

Growth hormone therapy and growth in children with Noonan's syndrome: results of 3 years' follow-up

Growth data from the first 3 yr of a multicenter study examining the efficacy and safety of recombinant human GH [rhGH; 4 IU (1.3 mg)/m(2).day, sc] in children with Noonan's syndrome (NS) are reported for 23 subjects. Sixteen male and seven female patients (age, 9.3 +/- 2.6 yr at onset of GH therapy, mean +/- SD; range, 4.8-13.7) were each assessed at 1, 2, and 3 yr after starting treatment. Comparisons were made with a group of eight subjects (six males and two females, age, 9.0 +/- 4.1 yr; range, 4.1-14.8) with NS, not treated with rhGH, measured over the same period. All treated subjects underwent annual cardiac assessment. Height SD score increased from -2.7 +/- 0.4 at the start of GH therapy to -1.9 +/- 0.9 3 yr later (P < 0.001, two-tailed t test). This corresponded to an increase in height from 116.1 +/- 13.2 to 137.3 +/- 14.0 cm. Height velocity increased from 4.4 +/- 1.7 cm/yr in the year before treatment to 8.4 +/- 1.7 (P < 0.001), 6.2 +/- 1.7 (P < 0.001), and 5.8 +/- 1.8 (P = 0.01, two-tailed t test compared with baseline) during the first, second, and third years of GH treatment, respectively. Height acceleration was not significant during the second or third years when pubertal subjects were excluded. The comparison group showed an increase in height from 116.0 +/- 19.8 to 131.9 +/- 21.1 cm over the 3 yr (height SD score, -2.7 +/- 0.6 to -2.4 +/- 0.7, P = 0.3). None of the 23 children developed hypertrophic cardiomyopathy during GH treatment. The increase in growth rate in NS resulting from 1 yr of GH therapy seems to be maintained during the second year, although height velocity shows a less significant increase over pretherapy values. Possible abnormal anabolic effects of rhGH on myocardial thickness were not confirmed, and no treated patient developed features of hypertrophic cardiomyopathy.

Novel mutations in the duplicated region of the polycystic kidney disease 1 (PKD1) gene provides supporting evidence for gene conversion

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common human single-gene disorders, and is the most common inherited form of cystic kidney disease. It is estimated that approximately 85% of ADPKD is due to mutations in the PKD1 gene, which is located on chromosome 16p13.3. Mutation analysis in this gene is difficult, because more than two-thirds of reiterated several times at 16p13.1. In this study, mutation screening in 90 ADPKD patients was carried out on exons in the duplicated region of the PKD1 gene (23-34), using genomic long-range PCR followed by nested PCR and single-strand conformation polymorphism (SSCP), and finally cycle sequencing. Two nonconservative missense mutations were detected in exons 25 and 31, and two conservative mutations were found in exons 24 and 29. A novel splicing mutation, which is expected to cause skipping of exon 30, was detected in one case. Moreover, six intronic variants, three silent variants, and one polymorphic variant were detected in this study. Comparison between some of these changes and published sequences from the homologous genes on 16p13.1, revealed supporting evidence for the gene conversion theory as a mechanism responsible for some of the mutations in the PKD1 gene. Factors likely to facilitate gene conversion in this region of the PKD1 gene are discussed.

Homozygosity at chromosome 8qter in individuals affected by mal de Meleda (Meleda disease) originating from the island of Meleda

BACKGROUND

The inherited palmoplantar keratodermas (PPKs) are a clinically heterogeneous group of disorders characterized by thickening of the skin of the palms and the soles. These diseases also exhibit genetic heterogeneity and many autosomal dominant and recessive forms have been described. Mal de Meleda (Meleda disease, MD) is an autosomal recessive form of PPK first described on the Dalmatian island of Meleda. A gene for MD has recently been assigned to the most telomeric portion of chromosome 8q using two large Algerian families.

OBJECTIVES

To determine whether the same gene underlies the skin disease in Meleda islanders.

METHODS

We have examined five affected individuals originating from the Dalmatian island itself for 8qter homozygosity.

RESULTS

This region was found to be homozygous in all five affected individuals but in none of the 20 other unaffected family members examined.

CONCLUSIONS

The current study confirms the localization of a gene for MD to 8qter using samples from the island of Meleda, highlighting the clinical and genetic homogeneity of this condition.

Study of hemoglobinopathies in Oman through a national register

OBJECTIVES

A national register of symptomatic hemoglobinopathies has been developed in Oman to facilitate the development of the National Program for the control of genetic blood disorders.

METHODS

The information was initially collected retrospectively through hospital records and was refined prospectively with data collected through a survey of pediatricians. The percentages of heterozygotes in different population groups and geographical locations, birth prevalence, age distribution of cases and factors determining frequencies of Hemoglobinopathies in different regions of the country were studied from the register.

RESULTS

The register has identified 1757 cases of homozygous Sickle Cell Anemia and 243 cases of beta-thalassemia major in a population of 1.5 million in 1995. Register based national figures of heterozygote carriers approximate 10% for Sickle Cell Anemia and 4% for beta-thalassemia major.

CONCLUSION

Defining regional and tribal variations can assist efficient targeting of health resources. This approach provides a simple model for other countries or regions to follow providing there is a health care system that facilitates registration.

Hearing impairment in 18q deletion syndrome

The 18q-syndrome is associated with hearing impairment in 50-80 per cent of cases. The hearing loss may be sensorineural or conductive. A high proportion of cases are associated with narrow or stenosed external auditory canals. This may be a useful clinical pointer to the syndrome. Two cases with impaired hearing are presented in this paper including one case with complex external ear and middle ear malformations. The clinical and audiological features in each case are described.

Further delineation of the DOOR syndrome

Two related sibships from an extended family have been observed with the features of the DOOR syndrome. These features included deafness, onychodystrophy, osteodystrophy, microcephaly, and global developmental retardation with progressive blindness. Seizures, which were associated with hypsarrhythmia, were frequent and difficult to control and ultimately were the cause of death in two patients. An MRI brain scan of case 1 showed a number of abnormalities including markedly reduced myelination. The urine organic acid analysis showed a ten-fold increase of 2-oxoglutarate. In one patient the placenta was noted to have multiple fluid filled cysts, which is a feature reported in other metabolic diseases. It is suggested that there may be genetic heterogeneity in the syndrome, and the presence of increased 2-oxoglutarate is associated with a more severe phenotype which is frequently lethal.

Transcervical sampling as a means of detection of fetal cells during the first trimester of pregnancy

OBJECTIVE

Our aim was to evaluate the detection of fetal cells from transcervical samples by means of fluorescence in situ hybridization analysis.

STUDY DESIGN

Forty-seven women undergoing first-trimester termination of pregnancy were recruited for transcervical sampling and 16 were recruited for endocervical mucus aspiration. Subjects were asked to assess the discomfort of the procedure. Fluorescence in situ hybridization analyses were performed with X and Y chromosome-specific probes. Results were compared with those of conventional chromosomal analysis.

RESULTS

Male signals (XY) were observed in 19 of 25 male fetuses (76%), and female signals (XX) were observed in 21 of 22 female fetuses. There was a significant variation between operators in cell retrieval. With mucus aspiration only 37.5% of male fetuses were correctly identified. The subjects did not find the procedure uncomfortable and reported that it was comparable to having a cervical smear taken.

CONCLUSIONS

Transcervical irrigation correctly identified the sex of 76% of male fetuses, but it still has considerable operator variability. This variability might be reduced by improved catheter design.

Recessive Robinow syndrome, allelic to dominant brachydactyly type B, is caused by mutation of ROR2

The autosomal recessive form of Robinow syndrome (RRS; MIM 268310) is a severe skeletal dysplasia with generalized limb bone shortening, segmental defects of the spine, brachydactyly and a dysmorphic facial appearance. We previously mapped the gene mutated in RRS to chromosome 9q22 (ref. 4), a region that overlaps the locus for autosomal dominant brachydactyly type B (refs 5,6). The recent identification of ROR2, encoding an orphan receptor tyrosine kinase, as the gene mutated in brachydactyly type B (BDB1; ref. 7) and the mesomelic dwarfing in mice homozygous for a lacZ and/or a neo insertion into Ror2 (refs 8,9) made this gene a candidate for RRS. Here we report homozygous missense mutations in both intracellular and extracellular domains of ROR2 in affected individuals from 3 unrelated consanguineous families, and a nonsense mutation that removes the tyrosine kinase domain and all subsequent 3' regions of the gene in 14 patients from 7 families from Oman. The nature of these mutations suggests that RRS is caused by loss of ROR2 activity. The identification of mutations in three distinct domains (containing Frizzled-like, kringle and tyrosine kinase motifs) indicates that these are all essential for ROR2 function.

A study of consanguinity in the Sultanate of Oman

Omani society has a long tradition of consanguinity, which goes back to pre-Islamic times. The aim of the present study was to determine the prevalence of consanguineous marriage and the mean coefficient of inbreeding in Oman. Consanguinity rates among 60,635 couples (20.8% of the national population of childbearing age) were determined on the basis of a questionnaire in major delivery units. In this large survey, which included all sections of the community, 24.1% of marriages were reported between first cousins and 11.8% of marriages were between second cousins. In addition, a further 20.4% of marriages were contracted within specific tribal groupings. Because of the strictly endogamous nature of the tribal groups in Oman, all marriages would be expected to be consanguineous to some degree, albeit at a level beyond that of second cousins (F < or = 0.0156). To obtain a more detailed picture of the patterns of consanguinity, and to assess the validity of the questionnaire-based study, 500 pedigrees were investigated in detail. The mean coefficient of inbreeding (alpha) in these pedigrees was 0.0204, compared with 0.0198 in the larger survey, suggesting that the data were broadly comparable and confirming the high degree of consanguinity in the population of Oman.

Linkage of recessive Robinow syndrome to a 4 cM interval on chromosome 9q22

Autosomal recessive Robinow syndrome is a form of mesomelic dwarfism with multiple rib and vertebral anomalies. Using autozygosity mapping we have identified a genetic locus (RBNW1) for this syndrome at chromosome 9q22 in seven consanguineous families from Oman. Our results indicate that the gene lies within a 4 cM region between markers D9S1836 and D9S1803 (maximum multipoint LOD score 12.3). In addition, we have analysed two non-Omani families with autosomal recessive Robinow and found no genetic heterogeneity.

A connexin 26 mutation causes a syndrome of sensorineural hearing loss and palmoplantar hyperkeratosis (MIM 148350)

We report a missense mutation in the connexin 26 gene (GJB2) in a family with an autosomal dominant syndrome of hearing loss and hyperkeratosis. The affected family members have high frequency, slowly progressive, bilateral, sensorineural hearing loss and palmoplantar hyperkeratosis. The mutation causes an amino acid substitution (G59A), which may disrupt a reverse turn in the first extracellular loop of connexin 26. Connexin 26 mutations have been reported in syndromes of deafness and palmoplantar keratoderma. These data provide additional evidence for the role of connexin 26 in syndromes of this type.

Novel nonsense mutation of the endothelin-B receptor gene in a family with Waardenburg-Hirschsprung disease

Waardenburg syndrome (WS) comprises sensorineural hearing loss, hypopigmentation of skin and hair, and pigmentary disturbances of the irides. Four types of WS have been classified to date; in WS type IV (WS4), patients additionally have colonic aganglionosis (Hirschsprung disease, HSCR). Mutations in the endothelin-3 (EDN3), endothelin-B receptor (EDNRB), and Sox10 genes have been identified as causative for WS type IV. We screened a family with a combined WS-HSCR phenotype for mutations in the EDNRB locus using standard DNA mutation analysis and sequencing techniques. We have identified a novel nonsense mutation at codon 253 (CGA-->TGA, Arg-->STOP). This mutation leads to a premature end of the translation of EDNRB at exon 3, and it is predicted to produce a truncated and nonfunctional endothelin-B receptor. All affected relatives were heterozygous for the Arg(253)-->STOP mutation, whereas it was not observed in over 50 unrelated individuals used as controls. These data confirm the role of EDNRB in the cause of the Waardenburg-Hirschsprung syndrome and demonstrate that in WS-HSCR there is a lack of correlation between phenotype and genotype and a variable expression of disease even within the same family.

Social, communicational, and behavioral deficits associated with ring X turner syndrome

We describe the cognitive and behavioral characteristics of five individuals with a ring X chromosome. All subjects had a small active (early replicating) ring X chromosome. The X inactive specific transcript (XIST) locus was confirmed by fluorescent in situ hybridisation (FISH) to be present in all ring X chromosomes. Mental retardation was present in four individuals. All patients with or without mental retardation had a characteristic profile of aggression toward self and others, episodes of screaming, attentional problems, and impulsiveness. Autistic-like features were also present in all individuals and included limited communication, obsessive compulsive behavior, and social difficulties. In some cases the obsessive behavior was extreme and incapacitating. This characteristic behavioral profile may aid the diagnosis and future understanding of ring X.

Splicing mutations in KCNQ1: a mutation hot spot at codon 344 that produces in frame transcripts

BACKGROUND

Long-QT syndrome is a monogenic disorder that produces cardiac arrhythmias and can lead to sudden death. At least 5 loci and 4 known genes exist in which mutations have been shown to be responsible for the disease. The potassium channel gene KCNQ1, previously named KVLQT1, on chromosome 11p15.5 is one of these.

METHODS AND RESULTS

We initially analyzed one family using microsatellite markers and found linkage to KCNQ1. Mutation detection showed a G to C change in the last base of exon 6 (1032 G-->C) that does not alter the coded alanine. Restriction digest analysis in the family showed that only affected individuals carried the mutation. A previous report suggested that a G to A substitution at the same position may act as a splice mutation in KCNQ1, but no data was given to support this hypothesis nor was the transcription product identified. We have shown by reverse-transcription polymerase chain reaction that 2 smaller bands were produced for the KCNQ1 gene transcripts in addition to the normal-sized transcripts when lymphocytes of affected individuals were analyzed. Sequencing these transcripts showed a loss of exon 7 in one and exons 6 and 7 in the other, but an in-frame transcript was left in each instance. We examined other families in whom long-QT syndrome was diagnosed and found another unreported splice-site mutation, 922-1 G-->C, in the acceptor site of intron 5, and 2 of the previously reported 1032 G-->A mutations. All these showed a loss of exons 6 and 7 in the mutant transcripts, validating the proposal that a consensus sequence is affected in the exonic mutations and that the integrity of the base at position 1032 is essential for correct processing of the transcript.

CONCLUSIONS

The 6 cases already reported in the literature with the 1032 G-->A transition, the novel 1032 G-->C transversion, and a recent G-->T transversion at the same base show that codon 344 is the second most frequently mutated after codon 341, suggesting at least two hotspots for mutations in KCNQ1.

Complex allele [-102T>A+S549R(T>G)] is associated with milder forms of cystic fibrosis than allele S549R(T>G) alone

We recently reported a novel complex allele in the cystic fibrosis transmembrane regulator (CFTR) gene, combining a sequence change in the minimal CFTR promoter (-102T>A) and a missense mutation in exon 11 [S549R(T>G)]. Here we compare the main clinical features of six patients with cystic fibrosis (CF) carrying the complex allele [-102T>A+S549R(T>G)] with those of 16 CF patients homozygous for mutation S549R(T>G) alone. Age at diagnosis was higher, and current age was significantly higher (P=0.0032) in the group with the complex allele, compared with the S549R/S549R group. Although the proportion of patients with lung colonization was similar in both groups, the age at onset was significantly higher in the group with the complex allele (P=0.0022). Patients with the complex allele also had significantly lower sweat test chloride values (P=0.0028) and better overall clinical scores (P=0.004). None of the 22 patients reported in this study had meconium ileus. All 16 patients homozygous for S549R(T>G), however, were pancreatic insufficient, as compared with 50% of patients carrying the complex allele (P=0.013). Moreover, the unique patient homozygous for [-102T>A+S549R(T>G)] presented with a mild disease at 34 years of age. These observations strongly suggest that the sequence change (-102T>A) in the CFTR minimal promoter could attenuate the severe clinical phenotype associated with mutation S549R(T>G).

Neural tube defects and congenital hydrocephalus in the Sultanate of Oman

A retrospective study was carried out in Oman to determine the incidence of neural tube defects (NTD) and congenital hydrocephalus (CH) and to identify any possible associations. National data retrieved from hospital records revealed the incidence of NTD in Oman to be comparatively low (1.25 per 1000), but the incidence of CH was much higher than that seen in Western Europe (0.44 per 1000) and was found to be associated with high rates of other congenital anomalies and neonatal death. There were no specific environmental factors associated with NTD and high environmental temperatures during the tropical desert summer (temperatures reach 48 degrees C) were excluded as a causative factor. In spina bifida families, later born children were more likely to be affected and there was also an association with increased maternal but not paternal age. Much higher consanguinity rates were noted in families with NTD and CH than in the general population.

Outcome of chromosomally normal livebirths with increased fetal nuchal translucency at 10-14 weeks' gestation

The aim of this study was to determine the outcome of chromosomally normal livebirths with increased fetal nuchal translucency at 10-14 weeks' gestation. Clinical follow up of 89 chromosomally normal livebirths that in fetal life had a minimum nuchal translucency thickness of 3.5 mm and a comparison group of 302 infants whose fetal nuchal translucency thickness at 10-14 weeks of gestation was less than 3.5 mm was performed. Major abnormalities, mainly structural defects of the cardiovascular or skeletal systems, were found in 10.1% (nine of 89) of the group with increased translucency, compared to 2% (five of 302) in those with translucency of less than 3.5 mm (chi2=11.9, p<0.001). Delay in achievement of developmental milestones was observed in one of the infants with increased translucency and in one of the comparison group. The findings of this study show that in chromosomally normal fetuses increased nuchal translucency thickness at 10-14 weeks of gestation is a marker for fetal abnormalities including structural defects and genetic syndromes.

The X-linked gene G4.5 is responsible for different infantile dilated cardiomyopathies

Barth syndrome (BTHS) is an X-linked disorder characterized clinically by the associated features of cardiac and skeletal myopathy, short stature, and neutropenia. The clinical manifestations of the disease are, in general, quite variable, but cardiac failure as a consequence of cardiac dilatation and hypertrophy is a constant finding and is the most common cause of death in the first months of life. X-linked cardiomyopathies with clinical manifestations similar to BTHS have been reported, and it has been proposed that they may be allelic. We have recently identified the gene responsible for BTHS, in one of the Xq28 genes, G4.5. In this paper we report the sequence analysis of 11 additional familial cases: 8 were diagnosed as possibly affected with BTHS, and 3 were affected with X-linked dilated cardiomyopathies. Mutations in the G4.5 gene were found in nine of the patients analyzed. The molecular studies have linked together what were formerly considered different conditions and have shown that the G4.5 gene is responsible for BTHS (OMIM 302060), X-linked endocardial fibroelastosis (OMIM 305300), and severe X-linked cardiomyopathy (OMIM 300069). Our results also suggest that very severe phenotypes may be associated with null mutations in the gene, whereas mutations in alternative portions or missense mutations may give a "less severe" phenotype.

Osteogenesis imperfecta with arthrogryposis multiplex congenita (Bruck syndrome)--evidence for possible autosomal recessive inheritance

We report a son and a daughter of a first cousin Pakistani marriage who both have osteogenesis imperfecta and the son in addition has arthrogryposis multiplex congenita. Bruck [(1897): Dtsch Med Wochenschr 23: 152-155] first reported the case of a boy who had multiple fractures and joint ankylosis, subsequently only one sibship with three affected cases and seven sporadic cases have been reported to our knowledge. On the basis of consanguinity this suggests that the association of osteogenesis imperfecta and arthrogryposis multiplex congenita is inherited in this family as an autosomal recessive condition with variable expression.

Hirschsprung's disease in Oman

The incidence of Hirschsprung's disease (HD) was studied retrospectively in Oman using hospital-based data. In Oman there is a single pediatric surgery unit where a register has been kept from 1989 to 1994, and because all cases are referred to this unit, a national survey could be carried out. There were 85 children with HD born between 1989 and 1994, and during the period there were 261,000 livebirths among Omani nationals. The population frequency in Oman is 1 in 3,070 (0.3/1,000). Eighty percent of cases presented in the first 6 months. The incidence in different regions and within different tribes of Oman was also studied. The highest frequency (1 in 1,800) is in the North Sharqiya region. There was not a significant seasonal influence in spite of the very high temperatures seen in the desert summer. The ratio of male to female cases was 2.9:1 overall, but less for longer-segment involvement. The consanguinity rate (first and second cousins) was 75%, which is higher than the level of consanguinity in the Omani population. Down's syndrome was observed in nine cases (11%), and a variety of other malformations were seen, including piebaldism, deafness, and HD in two sibships.