Nadia A. Akawi

Trafficking defects and loss of ligand binding are the underlying causes of all reported DDR2 missense mutations found in SMED-SL patients

Spondylo-meta-epiphyseal dysplasia (SMED) with short limbs and abnormal calcifications (SMED-SL) is a rare, autosomal recessive human growth disorder, characterized by disproportionate short stature, short limbs, short broad fingers, abnormal metaphyses and epiphyses, platyspondyly and premature calcifications. Recently, three missense mutations and one splice-site mutation in the DDR2 gene were identified as causative genetic defects for SMED-SL, but the underlying cellular and biochemical mechanisms were not explored. Here we report a novel DDR2 missense mutation, c.337G>A (p.E113K), that causes SMED-SL in two siblings in the United Arab Emirates. Another DDR2 missense mutation, c.2254C>T (p.R752C), matching one of the previously reported SMED-SL mutations, was found in a second affected family. DDR2 is a plasma membrane receptor tyrosine kinase that functions as a collagen receptor. We expressed DDR2 constructs with the identified point mutations in human cell lines and evaluated their localization and functional properties. We found that all SMED-SL missense mutants were defective in collagen-induced receptor activation and that the three previously reported mutants (p.T713I, p.I726R and p.R752C) were retained in the endoplasmic reticulum. The novel mutant (p.E113K), in contrast, trafficked normally, like wild-type DDR2, but failed to bind collagen. This finding is in agreement with our recent structural data identifying Glu113 as an important amino acid in the DDR2 ligand-binding site. Our data thus demonstrate that SMED-SL can result from at least two different loss-of-function mechanisms: namely defects in DDR2 targeting to the plasma membrane or the loss of its ligand-binding activity.

Discovery of four recessive developmental disorders using probabilistic genotype and phenotype matching among 4,125 families.

Discovery of most autosomal recessive disease-associated genes has involved analysis of large, often consanguineous multiplex families or small cohorts of unrelated individuals with a well-defined clinical condition. Discovery of new dominant causes of rare, genetically heterogeneous developmental disorders has been revolutionized by exome analysis of large cohorts of phenotypically diverse parent-offspring trios. Here we analyzed 4,125 families with diverse, rare and genetically heterogeneous developmental disorders and identified four new autosomal recessive disorders. These four disorders were identified by integrating Mendelian filtering (selecting probands with rare, biallelic and putatively damaging variants in the same gene) with statistical assessments of (i) the likelihood of sampling the observed genotypes from the general population and (ii) the phenotypic similarity of patients with recessive variants in the same candidate gene. This new paradigm promises to catalyze the discovery of novel recessive disorders, especially those with less consistent or nonspecific clinical presentations and those caused predominantly by compound heterozygous genotypes.

A homozygous mutation in the tight-junction protein JAM3 causes hemorrhagic destruction of the brain, subependymal calcification, and congenital cataracts.

The tight junction, or zonula occludens, is a specialized cell-cell junction that regulates epithelial and endothelial permeability, and it is an essential component of the blood-brain barrier in the cerebrovascular endothelium. In addition to functioning as a diffusion barrier, tight junctions are also involved in signal transduction. In this study, we identified a homozygous mutation in the tight-junction protein gene JAM3 in a large consanguineous family from the United Arab Emirates. Some members of this family had a rare autosomal-recessive syndrome characterized by severe hemorrhagic destruction of the brain, subependymal calcification, and congenital cataracts. Their clinical presentation overlaps with some reported cases of pseudo-TORCH syndrome as well as with cases involving mutations in occludin, another component of the tight-junction complex. However, massive intracranial hemorrhage distinguishes these patients from others. Homozygosity mapping identified the disease locus in this family on chromosome 11q25 with a maximum multipoint LOD score of 6.15. Sequence analysis of genes in the candidate interval uncovered a mutation in the canonical splice-donor site of intron 5 of JAM3. RT-PCR analysis of a patient lymphoblast cell line confirmed abnormal splicing, leading to a frameshift mutation with early termination. JAM3 is known to be present in vascular endothelium, although its roles in cerebral vasculature have not been implicated. Our results suggest that JAM3 is essential for maintaining the integrity of the cerebrovascular endothelium as well as for normal lens development in humans.

Change in meticillin-resistant Staphylococcus aureus clones at a tertiary care hospital in the United Arab Emirates over a 5-year period

Aims Meticillin-resistant Staphylococcus aureus (MRSA) strains isolated in Tawam Hospital, a tertiary care hospital in the United Arab Emirates, were examined in order to understand the reasons for a doubling of its incidence between 2003 and 2008 while maintaining the same infection control measures. Methods All consecutive non-duplicate clinically relevant MRSA isolates recovered between January and December 2003 and between May and October 2008 were studied. The antibiotic susceptibility, pulsed field gel electrophoresis, toxin gene, staphylococcal cassette chromosome mec (SCCmec), spa, agr and multilocus sequence types of the strains were tested. Results In 2003, typical healthcare-associated (HA-MRSA) genotypes (ST239-MRSA-III, ST22-MRSA-IV and ST5-MRSA-II) represented the majority (61.5%) of the isolates. By 2008 this pattern had changed and clonal types considered as community-associated (CA) MRSA comprised 73.1% of the strains with ST80-MRSA-IV, ST5-MRSA-IV and ST1-MRSA with non-typable SCCmec types being the most frequent. However, further epidemiological investigations showed that only one-third of the CA-MRSA infections were actually acquired in the community, indicating that CA-MRSA clones have entered and spread within the hospital. Conclusions The emergence of CA-MRSA clones with subsequent entry to and spread within the hospital has contributed to the increasing incidence of MRSA observed in Tawam Hospital and probably also in other hospitals in the UAE.

A mutation in KIF7 is responsible for the autosomal recessive syndrome of macrocephaly, multiple epiphyseal dysplasia and distinctive facial appearance

BackgroundWe previously reported the existence of a unique autosomal recessive syndrome consisting of macrocephaly, multiple epiphyseal dysplasia and distinctive facial appearance mapping to chromosome 15q26.MethodsIn this manuscript, we have used whole exome sequencing on two affected members of a consanguineous family with this condition and carried out detailed bioinformatics analysis to elucidate the causative mutation.ResultsOur analysis resulted in the identification of a homozygous p.N1060S missense mutation in a highly conserved residue in KIF7, a regulator of Hedgehog signaling that has been recently found to be causing Joubert syndrome, fetal hydrolethalus and acrocallosal syndromes. The phenotype in our patients partially overlaps with the phenotypes associated with those syndromes but they also exhibit some distinctive features including multiple epiphyseal dysplasia.ConclusionsWe report the first missense homozygous disease-causing mutation in KIF7 and expand the clinical spectrum associated with mutations in this gene to include multiple epiphyseal dysplasia. The missense nature of the mutation might account for the unique presentation in our patients.

Stüve–Wiedemann syndrome and related bent bone dysplasias

Akawi NA, Ali BR, Al‐Gazali L. Stüve–Wiedemann syndrome and related bent bone dysplasias.

METTL23, a transcriptional partner of GABPA, is essential for human cognition

Whereas many genes associated with intellectual disability (ID) encode synaptic proteins, transcriptional defects leading to ID are less well understood. We studied a large, consanguineous pedigree of Arab origin with seven members affected with ID and mild dysmorphic features. Homozygosity mapping and linkage analysis identified a candidate region on chromosome 17 with a maximum multipoint logarithm of odds score of 6.01. Targeted high-throughput sequencing of the exons in the candidate region identified a homozygous 4-bp deletion (c.169_172delCACT) in the METTL23 (methyltransferase like 23) gene, which is predicted to result in a frameshift and premature truncation (p.His57Valfs*11). Overexpressed METTL23 protein localized to both nucleus and cytoplasm, and physically interacted with GABPA (GA-binding protein transcription factor, alpha subunit). GABP, of which GABPA is a component, is known to regulate the expression of genes such as THPO (thrombopoietin) and ATP5B (ATP synthase, H+ transporting, mitochondrial F1 complex, beta polypeptide) and is implicated in a wide variety of important cellular functions. Overexpression of METTL23 resulted in increased transcriptional activity at the THPO promoter, whereas knockdown of METTL23 with siRNA resulted in decreased expression of ATP5B, thus revealing the importance of METTL23 as a regulator of GABPA function. The METTL23 mutation highlights a new transcriptional pathway underlying human intellectual function.

Identification of New Alleles and the Determination of Alleles and Genotypes Frequencies at the CYP2D6 Gene in Emiratis

CYP2D6 belongs to the cytochrome P450 superfamily of enzymes and plays an important role in the metabolism of 20–25% of clinically used drugs including antidepressants. It displays inter-individual and inter-ethnic variability in activity ranging from complete absence to excessive activity which causes adverse drug reactions and toxicity or therapy failure even at normal drug doses. This variability is due to genetic polymorphisms which form poor, intermediate, extensive or ultrarapid metaboliser phenotypes. This study aimed to determine CYP2D6 alleles and their frequencies in the United Arab Emirates (UAE) local population. CYP2D6 alleles and genotypes were determined by direct DNA sequencing in 151 Emiratis with the majority being psychiatric patients on antidepressants. Several new alleles have been identified and in total we identified seventeen alleles and 49 genotypes. CYP2D6*1 (wild type) and CYP2D6*2 alleles (extensive metaboliser phenotype) were found with frequencies of 39.1% and 12.2%, respectively. CYP2D6*41 (intermediate metaboliser) occurred in 15.2%. Homozygous CYP2D6*4 allele (poor metaboliser) was found with a frequency of 2% while homozygous and heterozygous CYP2D6*4 occurred with a frequency of 9%. CYP2D6*2xn, caused by gene duplication (ultrarapid metaboliser) had a frequency of 4.3%. CYP2D6 gene duplication/multiduplication occurred in 16% but only 11.2% who carried more than 2 active functional alleles were considered ultrarapid metabolisers. CYP2D6 gene deletion in one copy occurred in 7.5% of the study group. In conclusion, CYP2D6 gene locus is heterogeneous in the UAE national population and no significant differences have been identified between the psychiatric patients and controls.

Is autosomal recessive Silver–Russel syndrome a separate entity or is it part of the 3-M syndrome spectrum?†‡

Intrauterine growth retardation (IUGR) is a nonspecific finding that occurs in approximately 0.17% of all live‐births. However, IUGR can also be a significant feature of many recognized genetic syndromes including Silver–Russel syndrome (SRS), Three M syndrome (3‐M), Dubowitz syndrome, and Mulibrey nanism. Differentiation of 3‐M syndrome from autosomal recessive SRS has been difficult because of the phenotypic variability of the latter. Limb length asymmetry is seen in over half of those with autosomal recessive SRS, but not in individuals with 3‐M syndrome. Characteristic radiologic findings of 3‐M syndrome are not present in SRS. We used single nucleotide polymorphism (SNP) microarrays to investigate the cause of phenotypic features of SRS that shows autosomal recessive inheritance in three consanguineous families, two from United Arab Emirates (UAE), and one from Jordan. The mapped regions contained CUL7 and OBSL1, the genes that have recently been shown to cause 3‐M syndrome. Subsequently, direct DNA sequencing of CUL7 and OBSL1 genes revealed novel mutations in both genes including two mutations in OBSL1 [c.1119G>C (p.W373C) and c.681_682delinsTT (p.Q228X)], and a nonsense mutation in CUL7 [c.203G>A (p.W68X)]. In addition, a six nucleotide deletion in CUL7 [c.649_654delAGCCGC (p.217_218delSR)] was found in a consanguineous family from UAE that had the typical features of 3‐M. As a result of these findings, we question the identity of the autosomal recessive SRS and suggest that all apparently recessive SRS families should be tested for mutations in CUL7 and OBSL1.

Clinical and molecular analysis of UAE fibrochondrogenesis patients expands the phenotype and reveals two COL11A1 homozygous null mutations

Akawi NA, Al‐Gazali L, Ali BR. Clinical and molecular analysis of UAE fibrochondrogenesis patients expands the phenotype and reveals two COL11A1 homozygous null mutations.