Whole-genome analysis reveals that mutations in inositol polyphosphate phosphatase-like 1 cause opsismodysplasia.

Opsismodysplasia is a rare, autosomal-recessive skeletal dysplasia characterized by short stature, characteristic facial features, and in some cases severe renal phosphate wasting. We used linkage analysis and whole-genome sequencing of a consanguineous trio to discover that mutations in inositol polyphosphate phosphatase-like 1 (INPPL1) cause opsismodysplasia with or without renal phosphate wasting. Evaluation of 12 families with opsismodysplasia revealed that INPPL1 mutations explain ~60% of cases overall, including both of the families in our cohort with more than one affected child and 50% of the simplex cases.

New and known mutations associated with inborn errors of metabolism in a heterogeneous Middle Eastern population.

OBJECTIVE: To identify the mutations underlying a number of inborn errors of metabolism (IEM) disorders among United Arab Emirates (UAE) residents. METHODS: Molecular diagnostic and bioinformatics tools were used to identify the causative mutations of IEM disorders from multi-ethnic patients residing in UAE. The study was conducted in Al-Ain, UAE, between April 2009 and September 2010. This is a case series retrospective study where patients attending the metabolic clinic at Tawam Hospital were recruited. Thirty patients and 26 parents were included. RESULTS: We present evidence in the UAE of 7 new mutations and 19 mutations that have previously been reported in other populations, all causing a number of common IEM disorders, including phenylketonuria, maple syrup urine disease, glycogen storage diseases, beta-ketothiolase deficiency, and Zellweger syndrome among many others. CONCLUSION: Reflecting the diverse ethnic groups residing in the UAE, we found mutations in several different population groups. However, consanguinity is evident in most cases. This report is of utmost importance for taking the necessary steps toward the prevention of inherited disorders, not just in the UAE, but anywhere in the world where these Arab and Asian populations reside, or where consanguinity is a cultural norm.

Homozygous nonsense mutations in TWIST2 cause Setleis syndrome.

The focal facial dermal dysplasias (FFDDs) are a group of inherited developmental disorders in which the characteristic diagnostic feature is bitemporal scar-like lesions that resemble forceps marks. To date, the genetic defects underlying these ectodermal dysplasias have not been determined. To identify the gene defect causing autosomal-recessive Setleis syndrome (type III FFDD), homozygosity mapping was performed with genomic DNAs from five affected individuals and 26 members of the consanguineous Puerto Rican (PR) family originally described by Setleis and colleagues. Microsatellites D2S1397 and D2S2968 were homozygous in all affected individuals, mapping the disease locus to 2q37.3. Haplotype analyses of additional markers in the PR family and a consanguineous Arab family further limited the disease locus to approximately 3 Mb between D2S2949 and D2S2253. Of the 29 candidate genes in this region, the bHLH transcription factor, TWIST2, was initially sequenced on the basis of its known involvement in murine facial development. Homozygous TWIST2 nonsense mutations, c.324C>T and c.486C>T, were identified in the affected members of the Arab and PR families, respectively. Characterization of the expressed mutant proteins, p.Q65X and p.Q119X, by electrophoretic mobility shift assays and immunoblot analyses indicated that they were truncated and unstable. Notably, Setleis syndrome patients and Twist2 knockout mice have similar facial features, indicating the gene's conserved role in mammalian development. Although human TWIST2 and TWIST1 encode highly homologous bHLH transcription factors, the finding that TWIST2 recessive mutations cause an FFDD and dominant TWIST1 mutations cause Saethre-Chotzen craniocynostosis suggests that they function independently in skin and bone development.

A novel mutation in ARG1 gene is responsible for arginase deficiency in an Asian family.

Argininemia is a rare autosomal recessive metabolic disorder caused by a deficiency in the arginase enzyme, which is the final enzyme in the urea cycle and responsible for the hydrolysis of arginine to urea and ornithine. The disease becomes symptomatic during childhood and is characterized by progressive spastic quadriplegia, progressive mental impairment, growth retardation, and periodic episodes of hyperammonemia. At least 19 distinct mutations in the ARG1 gene have been identified indicating the molecular heterogeneity of this condition. We report a homozygous novel mutation (c.93 delG) in the ARG1 gene from 3 affected children of a Pakistani family living in the United Arab Emirates. The mutation is expected to lead to a frame shift after the thirtieth residue and a stop codon at residue 44 (p.T30fsX14). Therefore, this mutation is expected to result in complete loss-of-function of the arginase enzyme and therefore is the mostly likely cause of argininemia in this family.

Identification of CANT1 mutations in Desbuquois dysplasia.

Desbuquois dysplasia is a severe condition characterized by short stature, joint laxity, scoliosis, and advanced carpal ossification with a delta phalanx. Studying nine Desbuquois families, we identified seven distinct mutations in the Calcium-Activated Nucleotidase 1 gene (CANT1), which encodes a soluble UDP-preferring nucleotidase belonging to the apyrase family. Among the seven mutations, four were nonsense mutations (Del 5' UTR and exon 1, p.P245RfsX3, p.S303AfsX20, and p.W125X), and three were missense mutations (p.R300C, p.R300H, and p.P299L) responsible for the change of conserved amino acids located in the seventh nucleotidase conserved region (NRC). The arginine substitution at position 300 was identified in five out of nine families. The specific function of CANT1 is as yet unknown, but its substrates are involved in several major signaling functions, including Ca2+ release, through activation of pyrimidinergic signaling. Importantly, using RT-PCR analysis, we observed a specific expression in chondrocytes. We also found electron-dense material within distended rough endoplasmic reticulum in the fibroblasts of Desbuquois patients. Our findings demonstrate the specific involvement of a nucleotidase in the endochondral ossification process.

FREM1 mutations cause bifid nose, renal agenesis, and anorectal malformations syndrome.

An autosomal-recessive syndrome of bifid nose and anorectal and renal anomalies (BNAR) was previously reported in a consanguineous Egyptian sibship. Here, we report the results of linkage analysis, on this family and on two other families with a similar phenotype, which identified a shared region of homozygosity on chromosome 9p22.2-p23. Candidate-gene analysis revealed homozygous frameshift and missense mutations in FREM1, which encodes an extracellular matrix component of basement membranes. In situ hybridization experiments demonstrated gene expression of Frem1 in the midline of E11.5 mouse embryos, in agreement with the observed cleft nose phenotype of our patients. FREM1 is part of a ternary complex that includes FRAS1 and FREM2, and mutations of the latter two genes have been reported to cause Fraser syndrome in mice and humans. The phenotypic variability previously reported for different Frem1 mouse mutants suggests that the apparently distinct phenotype of BNAR in humans may represent a previously unrecognized variant of Fraser syndrome.

Cohen syndrome: report of nine cases and review of the literature, with emphasis on ophthalmic features.

PURPOSE: To review the clinical features of reported cases of Cohen syndrome with a focus on ophthalmic features and report nine new cases. METHODS: Retrospective case series and literature review. RESULTS: Cohen syndrome is a rare autosomal-recessive condition with about 136 reported cases. The typical phenotype of Cohen syndrome is variable and includes mild to severe psychomotor retardation, microcephaly, a cheerful disposition, characteristic facial features, childhood hypotonia and joint laxity, truncal obesity, intermittent neutropenia, along with a progressive retinal dystrophy and refractive myopia. We present nine cases that illustrate the typical clinical features of the disorder at different ages, including a woman with the less common finding of ectopia lentis. CONCLUSIONS: Cohen syndrome remains underdiagnosed or misdiagnosed by ophthalmologists. Awareness of this condition among ophthalmologists is important because the typical systemic and ophthalmologic findings may lead to an accurate diagnosis and counseling. Although diagnostic criteria exist based on clinical studies of patients with confirmed VPS13B (COH1) gene mutations, no minimal clinical diagnostic criteria are widely accepted at this time.

Sporadic Larsen syndrome in a preterm female originally diagnosed as positional deformities due to oligohydramnios.

Few reports describe incidental prenatal diagnosis of sporadic Larsen syndrome by ultrasound, but none of these discuss coincidental oligohydramnios or an association with fetal growth restriction. A 28-year-old woman had prolonged rupture of membranes causing marked oligohydramnios at 32 weeks gestation in her first pregnancy. Labor was induced by vaginal prostaglandins and oxytocin infusion after dexamethasone administration because of concern about placental abruption. She delivered vaginally a live female infant weighing 1960 g (< 10th percentile) with multiple skeletal malformations and characteristic facies originally suspected as positional. Newborn x-rays, however, established the diagnosis of Larsen syndrome with bilateral dislocations of the hips, knees (genu recurvatum), and ankles (club foot). The neonatal karyotype was 46,XX. Parental examination and family history were unremarkable. The newborn did well with bilateral lower extremities cast. Postnatal diagnosis of Larsen syndrome should be suspected in neonates with multiple skeletal abnormalities following oligohydramnios.

Extreme microcephaly with agyria-pachygyria, partial agenesis of the corpus callosum, and pontocerebellar dysplasia.

A 1-year-old boy with extreme microcephaly and a complex brain malformation is reported. Magnetic resonance imaging revealed an abnormal gyral pattern with features of the agyria-pachygyria spectrum, partial agenesis of the corpus callosum, severely hypoplastic posterior cerebellar vermis, and an abnormal foliation pattern of the cerebellar hemispheres associated with a flat and wide isthmus and pons. Although this phenotype shares some features with malformations classified as microcephaly with a simplified gyral pattern, microlissencephaly, or lissencephaly with cerebellar hypoplasia, none of the several subgroups of these categories are identical to the cerebral dysgenesis found in this patient.

Nevo syndrome is allelic to the kyphoscoliotic type of the Ehlers-Danlos syndrome (EDS VIA).

We report on seven patients affected with Nevo syndrome, a rare, autosomal recessive disorder characterized by increased perinatal length, kyphosis, muscular hypotonia, and joint laxity. Since its first description by Nevo et al. [1974], only a few cases have been reported. Because some of these patients present clinical features similar to those of the kyphoscoliotic type of Ehlers-Danlos syndrome (EDS VIA), an inherited connective tissue disorder characterized by a deficiency of lysyl hydroxylase due to mutations in PLOD1, we studied seven patients with Nevo syndrome, three of whom have previously been reported, and four of whom are new. In the five patients from whom urine was available, the ratio of total urinary lysyl pyridinoline (LP) to hydroxylysyl pyridinoline (HP) was elevated (8.2, 7.8, 8.6, 3.5, and 4.8, respectively) compared with that in controls (0.20 +/- 0.05, range 0.10-0.38), and similar to that observed in patients with EDS VIA (5.97 +/- 0.99, range 4.3-8.1). Six patients were homozygous for a point mutation in exon 9 of PLOD1 causing a p.R319X nonsense mutation, while one patient was homozygous for a large deletion comprising exon 17 of PLOD1. We conclude that the Nevo syndrome is allelic to and clinically indistinguishable from EDS VIA, and present evidence that increased length at birth and wristdrop, in addition to muscular hypotonia and kyphoscoliosis, should prompt the physician to consider EDS VIA earlier than heretofore.

Mutations in POMT1 are found in a minority of patients with Walker-Warburg syndrome.

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder of infancy characterized by hydrocephalus, agyria, retinal dysplasia, congenital muscular dystrophy, and over migration of neurons through a disrupted pial surface resulting in leptomeningeal heterotopia. Although previous work identified mutations in the o-mannosyl transferase, POMT1, in 6 out of 30 WWS families [Beltran-Valero de Bernabe et al., 2002], the incidence of POMT1 mutations in WWS is not known. We sequenced the entire coding region of POMT1 in 30 consecutive, unselected patients with classic WWS. Two novel heterozygous mutations were found in two patients from non-consanguineous parents, whereas 28 other patients failed to show any POMT1 mutations. One patient was found to be heterozygous for a transition, g.1233T > A, which predicts p.Y352X. A second patient was found also to be heterozygous for a transition g.1790C > G, which predicts p.S537R. As an additional determination of the frequency of the POMT1 mutations in WWS, we tested for linkage of WWS to POMT1 in six consanguineous families. All six demonstrated heterozygosity and negative LOD scores at the POMT1 locus. From these data we show that POMT1 is an uncommon cause of WWS, the incidence of coding region mutations in this population of WWS being less than 7%. We conclude that while the incidence of POMT1 mutations in WWS can be as high as 20% as reported by Beltran-Valero de Bernabe et al. [2002] and it can be as low as approximately 7%, as reported here.

Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux.

The homodimeric transmembrane receptor natriuretic peptide receptor B (NPR-B [also known as guanylate cyclase B, GC-B, and GUC2B]; gene name NPR2) produces cytoplasmic cyclic GMP from GTP on binding its extracellular ligand, C-type natriuretic peptide (CNP). CNP has previously been implicated in the regulation of skeletal growth in transgenic and knockout mice. The autosomal recessive skeletal dysplasia known as "acromesomelic dysplasia, type Maroteaux" (AMDM) maps to an interval that contains NPR2. We sequenced DNA from 21 families affected by AMDM and found 4 nonsense mutations, 4 frameshift mutations, 2 splice-site mutations, and 11 missense mutations. Molecular modeling was used to examine the putative protein change brought about by each missense mutation. Three missense mutations were tested in a functional assay and were found to have markedly deficient guanylyl cyclase activity. We also found that obligate carriers of NPR2 mutations have heights that are below the mean for matched controls. We conclude that, although NPR-B is expressed in a number of tissues, its major role is in the regulation of skeletal growth.

Null leukemia inhibitory factor receptor (LIFR) mutations in Stuve-Wiedemann/Schwartz-Jampel type 2 syndrome.

Stuve-Wiedemann syndrome (SWS) is a severe autosomal recessive condition characterized by bowing of the long bones, with cortical thickening, flared metaphyses with coarsened trabecular pattern, camptodactyly, respiratory distress, feeding difficulties, and hyperthermic episodes responsible for early lethality. Clinical overlap with Schwartz-Jampel type 2 syndrome (SJS2) has suggested that SWS and SJS2 could be allelic disorders. Through studying a series of 19 families with SWS/SJS2, we have mapped the disease gene to chromosome 5p13.1 at locus D5S418 (Zmax=10.66 at theta =0) and have identified null mutations in the leukemia inhibitory factor receptor (LIFR or gp190 chain) gene. A total of 14 distinct mutations were identified in the 19 families. An identical frameshift insertion (653_654insT) was identified in families from the United Arab Emirates, suggesting a founder effect in that region. It is interesting that 12/14 mutations predicted premature termination of translation. Functional studies indicated that these mutations alter the stability of LIFR messenger RNA transcripts, resulting in the absence of the LIFR protein and in the impairment of the JAK/STAT3 signaling pathway in patient cells. We conclude, therefore, that SWS and SJS2 represent a single clinically and genetically homogeneous condition due to null mutations in the LIFR gene on chromosome 5p13.

Birth prevalence and pattern of osteochondrodysplasias in an inbred high risk population.

BACKGROUND: Define the pattern and birth prevalence of the different types of osteochondrodysplasias in newborn infants in the United Arab Emirates (UAE) population, which is highly inbred and where termination of pregnancy is not accepted. METHODS: All infants with a birth weight of 500 gm and above in the three hospitals in Al Ain Medical District of the UAE were studied prospectively over a period of 5 years. For each live birth or stillbirth with suspected skeletal dysplasia, a detailed clinical and radiological examination was carried out. Pregnancy history and information regarding parental age, ethnic origin, family history, and level of consanguinity were obtained and a pedigree was constructed. RESULTS: Among the 38,048 births during the study period, 36 (9.46/10,000 births) had some type of skeletal dysplasia. Eighteen cases were attributed to autosomal recessive genes (4.7/10,000 births), 10 were due to apparent new dominant mutations (2.62/10,000), five were autosomal dominant type (1.3/10,000) and one was X-linked dominant type (0.26/10,000). In three cases, inheritance was unknown. The most common recessive type of skeletal dysplasia in our series was fibrochondrogenesis (1.05/10,000), followed by chondrodysplasia punctata (0.78/10,000). The birth prevalence rate of skeletal dysplasia doubled in the last 2 years of the 5-year observation period (6.74/10,000 in 1996 vs. 12.86/10,000 in 1999, and 13.45/10,000 in 2000). This increase involved cases caused by new dominant mutations, and occurred mainly in the first half of 1999. CONCLUSION: This prospective study has identified a high birth prevalence of skeletal dysplasia, and risk factors are postulated. These findings represent an accurate birthprevalence figure and a useful baseline for this group of birth defects in the UAE.

Folic acid awareness and intake survey in the United Arab Emirates.

OBJECTIVE: The aim of this study was to determine the level of knowledge and use of periconceptional folic acid supplementation in a sample of postpartum women recruited from three hospitals. DESIGN: Cross-sectional survey in which a structured questionnaire was used in a face-to-face encounter between the subject and a trained nurse. SETTINGS: Two teaching hospitals associated with Faculty of Medicine and Health Sciences and one private hospital. SUBJECTS: Postpartum women in the three hospitals were recruited during a 40-day period in November 1999. Women who did not agree to participate, had complicated labor, delivered babies with congenital malformations, or were too exhausted or difficult to examine, were excluded. RESULTS: Univariate analyses showed that overall 46.4% of the respondents had heard about folic acid and only 8.7% knew that it prevented birth defects. 45.5% of respondents took folic acid in the first trimester. The percentage of women who had ever heard about folic acid was higher in those with higher education, and those who were not UAE nationals. Use of folic acid was associated with non-UAE nationality. CONCLUSION: Awareness of the value of periconceptional folic acid was very low and use of folic acid was less prevalent among women of UAE nationality.

Mutations in a novel gene Dymeclin (FLJ20071) are responsible for Dyggve-Melchior-Clausen syndrome.

Dyggve-Melchior-Clausen syndrome (DMC) is a rare autosomal-recessive disorder, the gene for which maps to chromosome 18q21.1. DMC is characterized by the association of a spondylo-epi-metaphyseal dysplasia and mental retardation. Electron microscopic study of cutaneous cells of an affected child showed dilated rough endoplasmic reticulum, enlarged and aberrant vacuoles and numerous vesicles. As the etiology of the disorder is unknown, we have used a positional cloning strategy to identify the DMC gene. We detected seven deleterious mutations within a gene predicted from a human transcript (FLJ20071) in 10 DMC families. The mutations were nonsense mutations (R194X, R204X, L219X, Q483X), splice site or frameshift mutations (K626N+92aa to stop). The DMC gene transcript is widely distributed but appears abundant in chondrocytes and fetal brain. The predicted protein product of the DMC gene yields little insight into its likely function, showing no significant homology to any known protein family. However, the carboxy terminal end comprises a cluster of dileucine motifs, highly conserved across species. We conclude that DMC syndrome is consequent upon loss of function of a gene that we propose to name Dymeclin, which may have a role in process of intracellular digestion of proteins.