Joshi Stephen

Mutations in human homologue of chicken talpid3 gene (KIAA0586) cause a hybrid ciliopathy with overlapping features of Jeune and Joubert syndromes

Background In chicken, loss of TALPID3 results in non-functional cilia and short-rib polydactyly syndrome. This phenotype is caused by a frameshift mutation in the chicken ortholog of the human KIAA0586 gene, which encodes a novel coiled-coil domain protein essential for primary ciliogenesis, suggesting that KIAA0586 can be associated with ciliopathy in human beings. Methods In our patients with ciliopathy (http://www.clinicaltrials.gov: NCT00068224), we have collected extensive clinical and neuroimaging data from affected individuals, and performed whole exome sequencing on DNA from affected individuals and their parents. We analysed gene expression on fibroblast cell line, and determined the effect of gene mutation on ciliogenesis in cells derived from patients. Results We identified biallelic mutations in the human TALPID3 ortholog, KIAA0586, in six children with findings of overlapping Jeune and Joubert syndromes. Fibroblasts cultured from one of the patients with Jeune–Joubert syndrome exhibited more severe cilia defects than fibroblasts from patients with only Joubert syndrome; this difference was reflected in KIAA0586 RNA expression levels. Rescue of the cilia defect with full-length wild type KIAA0586 indicated a causal link between cilia formation and KIAA0586 function. Conclusions Our results show that biallelic deleterious mutations in KIAA0586 lead to Joubert syndrome with or without Jeune asphyxiating thoracic dystrophy. Furthermore, our results confirm that KIAA0586/TALPID3 is essential in cilia formation in human beings, expand the KIAA0586 phenotype to include features of Jeune syndrome and provide a pathogenetic connection between Joubert and Jeune syndromes, based on aberrant ciliogenesis.

Congenital protein losing enteropathy: an inborn error of lipid metabolism due to DGAT1 mutations

Protein-losing enteropathy (PLE) is a clinical disorder of protein loss from the gastrointestinal system that results in hypoproteinemia and malnutrition. This condition is associated with a wide range of gastrointestinal disorders. Recently, a unique syndrome of congenital PLE associated with biallelic mutations in the DGAT1 gene has been reported in a single family. We hypothesize that mutations in this gene are responsible for undiagnosed cases of PLE in infancy. Here we investigated three children in two families presenting with severe diarrhea, hypoalbuminemia and PLE, using clinical studies, homozygosity mapping, and exome sequencing. In one family, homozygosity mapping using SNP arrays revealed the DGAT1 gene as the best candidate gene for the proband. Sequencing of all the exons including flanking regions and promoter regions of the gene identified a novel homozygous missense variant, p.(Leu295Pro), in the highly conserved membrane-bound O-acyl transferase (MBOAT) domain of the DGAT1 protein. Expression studies verified reduced amounts of DGAT1 in patient fibroblasts. In a second family, exome sequencing identified a previously reported splice site mutation in intron 8. These cases of DGAT1 deficiency extend the molecular and phenotypic spectrum of PLE, suggesting a re-evaluation of the use of DGAT1 inhibitors for metabolic disorders including obesity and diabetes.

Cystic cerebellar dysplasia and biallelic LAMA1 mutations: a lamininopathy associated with tics, obsessive compulsive traits and myopia due to cell adhesion and migration defects

Background Laminins are heterotrimeric complexes, consisting of α, β and γ subunits that form a major component of basement membranes and extracellular matrix. Laminin complexes have different, but often overlapping, distributions and functions. Methods Under our clinical protocol, NCT00068224, we have performed extensive clinical and neuropsychiatric phenotyping, neuroimaging and molecular analysis in patients with laminin α1 (LAMA1)-associated lamininopathy. We investigated the consequence of mutations in LAMA1 using patient-derived fibroblasts and neuronal cells derived from neuronal stem cells. Results In this paper we describe individuals with biallelic mutations in LAMA1, all of whom had the cerebellar dysplasia, myopia and retinal dystrophy, in addition to obsessive compulsive traits, tics and anxiety. Patient-derived fibroblasts have impaired adhesion, reduced migration, abnormal morphology and increased apoptosis due to impaired activation of Cdc42, a member of the Rho family of GTPases that is involved in cytoskeletal dynamics. LAMA1 knockdown in human neuronal cells also showed abnormal morphology and filopodia formation, supporting the importance of LAMA1 in neuronal migration, and marking these cells potentially useful tools for disease modelling and therapeutic target discovery. Conclusion This paper broadens the phenotypes associated with LAMA1 mutations. We demonstrate that LAMA1 deficiency can lead to alteration in cytoskeletal dynamics, which may invariably lead to alteration in dendrite growth and axonal formation. Estimation of disease prevalence based on population studies in LAMA1 reveals a prevalence of 1–20 in 1 000 000. Trial registration number: NCT00068224

CELSR2, encoding a planar cell polarity protein, is a putative gene in Joubert syndrome with cortical heterotopia, microophthalmia, and growth hormone deficiency

Joubert syndrome is a ciliopathy characterized by a specific constellation of central nervous system malformations that result in the pathognomonic “molar tooth sign” on imaging. More than 27 genes are associated with Joubert syndrome, but some patients do not have mutations in any of these genes. Celsr1, Celsr2, and Celsr3 are the mammalian orthologues of the drosophila planar cell polarity protein, flamingo; they play important roles in neural development, including axon guidance, neuronal migration, and cilium polarity. Here, we report bi‐allelic mutations in CELSR2 in a Joubert patient with cortical heterotopia, microophthalmia, and growth hormone deficiency.

Cellular and molecular defects in a patient with Hermansky-Pudlak syndrome type 5

Hermansky-Pudlak syndrome (HPS) is a heterogeneous group of genetic disorders typically manifesting with tyrosinase-positive oculocutaneous albinism, bleeding diathesis, and pulmonary fibrosis, in some subtypes. Most HPS subtypes are associated with defects in Biogenesis of Lysosome-related Organelle Complexes (BLOCs), which are groups of proteins that function together in the formation and/or trafficking of lysosomal-related endosomal compartments. BLOC-2, for example, consists of the proteins HPS3, HPS5, and HPS6. Here we present an HPS patient with defective BLOC-2 due to a novel intronic mutation in HPS5 that activates a cryptic acceptor splice site. This mutation leads to the insertion of nine nucleotides in-frame and results in a reduced amount of HPS5 at the transcript and protein level. In studies using skin fibroblasts derived from the proband and two other individuals with HPS-5, we found a perinuclear distribution of acidified organelles in patient cells compared to controls. Our results suggest the role of HPS5 in the endo-lysosomal dynamics of skin fibroblasts.

Mutations in KIAA0753 cause Joubert syndrome associated with growth hormone deficiency

Joubert syndrome and related disorders (JSRD) are a heterogeneous group of ciliopathies defined based on the mid-hindbrain abnormalities that result in the characteristic “molar tooth sign” on brain imaging. The core clinical findings of JSRD are hypotonia, developmental delay, abnormal eye movements and breathing abnormalities. To date, more than 30 JSRD genes that encode proteins important for structure and/or function of cilia have been identified. Here, we present 2 siblings with Joubert syndrome associated with growth hormone deficiency. Whole exome sequencing of the family identified compound heterozygous mutations in KIAA0753, i.e., a missense mutation (p.Arg257Gly) and an intronic mutation (c.2359-1G>C). The intronic mutation alters normal splicing by activating a cryptic acceptor splice site in exon 16. The novel acceptor site skips nine nucleotides, deleting three amino acids from the protein coding frame. KIAA0753 (OFIP) is a centrosome and pericentriolar satellite protein, previously not known to cause Joubert syndrome. We present comprehensive clinical descriptions of the Joubert syndrome patients as well as the cellular phenotype of defective ciliogenesis in the patients’ fibroblasts.

Biallelic SCN10A mutations in neuromuscular disease and epileptic encephalopathy

Two consanguineous families, one of Sudanese ethnicity presenting progressive neuromuscular disease, severe cognitive impairment, muscle weakness, upper motor neuron lesion, anhydrosis, facial dysmorphism, and recurrent seizures and the other of Egyptian ethnicity presenting with neonatal hypotonia, bradycardia, and recurrent seizures, were evaluated for the causative gene mutation.

TMEM231 Gene Conversion Associated with Joubert and Meckel-Gruber Syndromes in the Same Family.

Joubert and Meckel–Gruber syndromes (JS and MGS) are ciliopathies with overlapping features. JS patients manifest the “molar tooth sign” on brain imaging and variable eye, kidney, and liver disease. MGS presents with polycystic kidneys, occipital encephalocele, and polydactyly; it is typically perinatally fatal. Both syndromes are genetically heterogeneous; some genes cause either syndrome. Here, we report two brothers married to unrelated women. The first brother had three daughters with JS and a son with polycystic kidneys who died at birth. The second brothers wife had a fetal demise due to MGS. Whole exome sequencing identified TMEM231 NM_001077416.2: c.784G>A; p.(Asp262Asn) in all children and the wife of the first brother; the second brothers wife had a c.406T>G;p.(Trp136Gly) change. In‐depth analysis uncovered a rare gene conversion event in TMEM231, leading to loss of exon 4, in all the affected children of first brother. We believe that the combination of this gene conversion with different missense mutations led to a spectrum of phenotypes that span JS and MGS.

Identification of an Alu element-mediated deletion in the promoter region of GNE in siblings with GNE myopathy

GNE myopathy is a rare genetic disease characterized by progressive muscle atrophy and weakness. It is caused by biallelic mutations in the GNE gene that encodes for the bifunctional enzyme, uridine diphosphate (UDP)‐N‐acetylglucosamine (GlcNAc) 2‐epimerase/N‐acetylmannosamine (ManNAc) kinase. Typical characteristics of GNE myopathy include progressive myopathy, first involving anterior tibialis muscle and sparing the quadriceps, and rimmed vacuoles on muscle biopsy. Identifying biallelic mutations by sequencing of the GNE gene confirms the diagnosis of GNE myopathy. In a subset of patients, diagnostic confirmation is challenged by the identification of mutations in only one allele, suggesting mutations in deep intronic regions or regulatory regions.

Cortical atrophy and hypofibrinogenemia due to FGG and TBCD mutations in a single family: a case report

BackgroundBlended phenotypes or co-occurrence of independent phenotypically distinct conditions are extremely rare and are due to coincidence of multiple pathogenic mutations, especially due to consanguinity. Hereditary fibrinogen deficiencies result from mutations in the genes FGA, FGB, and FGG, encoding the three different polypeptide chains that comprise fibrinogen. Neurodevelopmental abnormalities have not been associated with fibrinogen deficiencies. In this study, we report an unusual patient with a combination of two independently inherited genetic conditions; fibrinogen deficiency and early onset cortical atrophy.Case presentationThe study describes a male child from consanguineous family presented with hypofibrinogenemia, diffuse cortical atrophy, microcephaly, hypertonia and axonal motor neuropathy. Through a combination of homozygosity mapping and exome sequencing, we identified bi-allelic pathogenic mutations in two genes: a homozygous novel truncating mutation in FGG (c.554del; p.Lys185Argfs*14) and a homozygous missense mutation in TBCD (c.1423G > A;p.Ala475Thr). Loss of function mutations in FGG have been associated with fibrinogen deficiency, while the c.1423G > A mutation in TBCD causes a novel syndrome of neurodegeneration and early onset encephalopathy.ConclusionsOur study highlights the importance of homozygosity mapping and exome sequencing in molecular prenatal diagnosis, especially when multiple gene mutations are responsible for the phenotype.