Adila Al-Kindy

Mutations in TMEM216 perturb ciliogenesis and cause Joubert, Meckel and related syndromes

Joubert syndrome (JBTS), related disorders (JSRDs) and Meckel syndrome (MKS) are ciliopathies. We now report that MKS2 and CORS2 (JBTS2) loci are allelic and caused by mutations in TMEM216, which encodes an uncharacterized tetraspan transmembrane protein. Individuals with CORS2 frequently had nephronophthisis and polydactyly, and two affected individuals conformed to the oro-facio-digital type VI phenotype, whereas skeletal dysplasia was common in fetuses affected by MKS. A single G218T mutation (R73L in the protein) was identified in all cases of Ashkenazi Jewish descent (n = 10). TMEM216 localized to the base of primary cilia, and loss of TMEM216 in mutant fibroblasts or after knockdown caused defective ciliogenesis and centrosomal docking, with concomitant hyperactivation of RhoA and Dishevelled. TMEM216 formed a complex with Meckelin, which is encoded by a gene also mutated in JSRDs and MKS. Disruption of tmem216 expression in zebrafish caused gastrulation defects similar to those in other ciliary morphants. These data implicate a new family of proteins in the ciliopathies and further support allelism between ciliopathy disorders.

Coffin–Siris syndrome is a SWI/SNF complex disorder

Coffin–Siris syndrome (CSS) is a congenital disorder characterized by intellectual disability, growth deficiency, microcephaly, coarse facial features, and hypoplastic or absent fifth fingernails and/or toenails. We previously reported that five genes are mutated in CSS, all of which encode subunits of the switch/sucrose non‐fermenting (SWI/SNF) ATP‐dependent chromatin‐remodeling complex: SMARCB1, SMARCA4, SMARCE1, ARID1A, and ARID1B. In this study, we examined 49 newly recruited CSS‐suspected patients, and re‐examined three patients who did not show any mutations (using high‐resolution melting analysis) in the previous study, by whole‐exome sequencing or targeted resequencing. We found that SMARCB1, SMARCA4, or ARID1B were mutated in 20 patients. By examining available parental samples, we ascertained that 17 occurred de novo. All mutations in SMARCB1 and SMARCA4 were non‐truncating (missense or in‐frame deletion) whereas those in ARID1B were all truncating (nonsense or frameshift deletion/insertion) in this study as in our previous study. Our data further support that CSS is a SWI/SNF complex disorder.

Genotype-phenotype associations in neurofibromatosis type 1 (NF1): an increased risk of tumor complications in patients with NF1 splice-site mutations?

Neurofibromatosis type 1 (NF1) is a complex neurocutaneous disorder with an increased susceptibility to develop both benign and malignant tumors but with a wide spectrum of inter and intrafamilial clinical variability. The establishment of genotype-phenotype associations in NF1 is potentially useful for targeted therapeutic intervention but has generally been unsuccessful, apart from small subsets of molecularly defined patients. The objective of this study was to evaluate the clinical phenotype associated with the specific types of NF1 mutation in a retrospectively recorded clinical dataset comprising 149 NF1 mutation-known individuals from unrelated families. Each patient was assessed for ten NF1-related clinical features, including the number of café-au-lait spots, cutaneous and subcutaneous neurofibromas and the presence/absence of intertriginous skin freckling, Lisch nodules, plexiform and spinal neurofibromas, optic gliomas, other neoplasms (in particular CNS gliomas, malignant peripheral nerve sheath tumors (MPNSTs), juvenile myelomonocytic leukemia, rhabdomyosarcoma, phaechromocytoma, gastrointestinal stromal tumors, juvenile xanthogranuloma, and lipoma) and evidence of learning difficulties. Gender and age at examination were also recorded. Patients were subcategorized according to their associated NF1 germ line mutations: frame shift deletions (52), splice-site mutations (23), nonsense mutations (36), missense mutations (32) and other types of mutation (6). A significant association was apparent between possession of a splice-site mutation and the presence of brain gliomas and MPNSTs (p = 0.006). If confirmed, these findings are likely to be clinically important since up to a third of NF1 patients harbor splice-site mutations. A significant influence of gender was also observed on the number of subcutaneous neurofibromas (females, p = 0.009) and preschool learning difficulties (females, p = 0.022).

Heterogeneity of mutational mechanisms and modes of inheritance in auriculocondylar syndrome

Background Auriculocondylar syndrome (ACS) is a rare craniofacial disorder consisting of micrognathia, mandibular condyle hypoplasia and a specific malformation of the ear at the junction between the lobe and helix. Missense heterozygous mutations in the phospholipase C, β 4 (PLCB4) and guanine nucleotide binding protein (G protein), α inhibiting activity polypeptide 3 (GNAI3) genes have recently been identified in ACS patients by exome sequencing. These genes are predicted to function within the G protein-coupled endothelin receptor pathway during craniofacial development. Results We report eight additional cases ascribed to PLCB4 or GNAI3 gene lesions, comprising six heterozygous PLCB4 missense mutations, one heterozygous GNAI3 missense mutation and one homozygous PLCB4 intragenic deletion. Certain residues represent mutational hotspots; of the total of 11 ACS PLCB4 missense mutations now described, five disrupt Arg621 and two disrupt Asp360. The narrow distribution of mutations within protein space suggests that the mutations may result in dominantly interfering proteins, rather than haploinsufficiency. The consanguineous parents of the patient with a homozygous PLCB4 deletion each harboured the heterozygous deletion, but did not present the ACS phenotype, further suggesting that ACS is not caused by PLCB4 haploinsufficiency. In addition to ACS, the patient harbouring a homozygous deletion presented with central apnoea, a phenotype that has not been previously reported in ACS patients. Conclusions These findings indicate that ACS is not only genetically heterogeneous but also an autosomal dominant or recessive condition according to the nature of the PLCB4 gene lesion.

Molecular genetic analysis of 30 families with Joubert syndrome

Joubert syndrome (JS) is rare recessive disorders characterized by the combination of hypoplasia/aplasia of the cerebellar vermis, thickened and elongated superior cerebellar peduncles, and a deep interpeduncular fossa which is defined by neuroimaging and is termed the ‘molar tooth sign’. JS is genetically highly heterogeneous, with at least 29 disease genes being involved. To further understand the genetic causes of JS, we performed whole‐exome sequencing in 24 newly recruited JS families. Together with six previously reported families, we identified causative mutations in 25 out of 30 (24 + 6) families (83.3%). We identified eight mutated genes in 27 (21 + 6) Japanese families, TMEM67 (7/27, 25.9%) and CEP290 (6/27, 22.2%) were the most commonly mutated. Interestingly, 9 of 12 CEP290 disease alleles were c.6012‐12T>A (75.0%), an allele that has not been reported in non‐Japanese populations. Therefore c.6012‐12T>A is a common allele in the Japanese population. Importantly, one Japanese and one Omani families carried compound biallelic mutations in two distinct genes (TMEM67/RPGRIP1L and TMEM138/BBS1, respectively). BBS1 is the causative gene in Bardet–Biedl syndrome. These concomitant mutations led to severe and/or complex clinical features in the patients, suggesting combined effects of different mutant genes.

Constitutional trisomy 8 mosaicism syndrome: case report and review.

Trisomy 8 mosaicism (Warkany syndrome) is a rare viable condition with variable phenotypes, ranging from mild dysmorphic features to severe malformations. Karyotyping and fluorescence in-situ hybridization potentially help detecting this low mosaic clone to confirm the diagnosis of patients with classical and unusual clinical presentations. This report reviews few previous cases to describe our case - a boy who had trisomy 8 mosaicism with severe dysmorphic features, born to a consanguineous Arabic couple. This study concludes that careful cytogenetic diagnoses of trisomy 8 mosaicism is essential for appropriate management and follow up of this rare disorder.

One in Three: Congenital Bent Bone Disease and Intermittent Hyperthermia in Three Siblings with Stuve-Wiedemann Syndrome

Stuve-Wiedemann syndrome (STWS) is a rare disorder characterised by congenital bowing of the long bones, contractures of the joints, neonatal onset of respiratory distress, sucking and swallowing difficulties, dysautonomia presenting as episodic hyperthermia, and usually an early death. Three siblings from a consanguineous marriage presented with similar clinical features over 16 years. STWS was established with their last child at the beginning of 2012. All the children exhibited the onset of STWS in the neonatal period with fever and generalised hypotonia. Examinations of all the infants revealed camptodactyly, micrognathia, bent long bones with wide metaphyses, and hypotonia. Only the second affected child had myotonia, demonstrated by electromyography. Unusual pyrexia as a presenting feature in this syndrome needs early recognition so that extensive and elaborate investigations can be avoided. The disorder is usually caused by a mutation in the leukaemia inhibitory factor receptor gene.

Existing Challenges Associated with Offering Prenatal Genetic Diagnosis in an Arab Society in the Sultanate of Oman

The incidence of congenital anomalies and/or genetic disorders in the Omani population has reached figures greater than double the global statistics. Preference for consanguineous unions together with the fact that termination of pregnancy in Muslim communities are largely avoided, have been highlighted as contributing factors. This overview identifies a third significant aspect contributing to the elevated rate of genetic disorders in the Omani population. Namely, a lack of services that are able to offer termination of pregnancy for severe congenital anomalies, to requesting parents. In this report we select an unusual case of a family at risk for two distinct genetic disorders - 6q micro-deletion and unbalanced products of conception attributed to a balanced parental translocation involving chromosome 3 and 13, to portray and examine the current situation faced by Omani couples interested in prenatal diagnosis for termination of pregnancy. Additional challenges and pitfalls to developing a prenatal diagnostic service as part of the genetic service in Oman are discussed.

A rare case of de novo mosaicism: Deletion 18p and isochromosome 18q syndrome

Monosomy 18p syndrome is a rare chromosomal disorder with varying phenotypic and clinical manifestations. Dysmorphism, growth delay, delayed speech and mental retardation are a few of the commonest features observed. The cytogenetic findings also vary and may comprise a pure deletion of the entire 18p arm or a deletion of a part of the 18p arm, if involved in a translocation with other chromosomes. Monosomy 18p may either occur by itself or with a structural alteration of the remaining chromosome 18, as a ring or as an isochromosome. The clinical presentation of this syndrome often overlaps with other syndromes. Establishing a cytogenetic diagnosis and understanding the location of the breakpoints is crucial for precise management and follow-up. We present here a rare case with mosaicism for a de novo deletion of 18p with isochromosome 18q in a boy born to a consanguineous Omani couple.