Ciliopathies are highly heterogeneous clinical disorders of the primary cilium. We aim to characterize a large cohort of ciliopathies phenotypically and molecularly.
Detailed phenotypic and genomic ...analysis of patients with ciliopathies, and functional characterization of novel candidate genes.
In this study, we describe 125 families with ciliopathies and show that deleterious variants in previously reported genes, including cryptic splicing variants, account for 87% of cases. Additionally, we further support a number of previously reported candidate genes (BBIP1, MAPKBP1, PDE6D, and WDPCP), and propose nine novel candidate genes (CCDC67, CCDC96, CCDC172, CEP295, FAM166B, LRRC34, TMEM17, TTC6, and TTC23), three of which (LRRC34, TTC6, and TTC23) are supported by functional assays that we performed on available patient-derived fibroblasts. From a phenotypic perspective, we expand the phenomenon of allelism that characterizes ciliopathies by describing novel associations including WDR19-related Stargardt disease and SCLT1- and CEP164-related Bardet-Biedl syndrome.
In this cohort of phenotypically and molecularly characterized ciliopathies, we draw important lessons that inform the clinical management and the diagnostics of this class of disorders as well as their basic biology.
Objective
Autosomal recessive primary microcephaly (MCPH) is a rare condition characterized by a reduced cerebral cortex accompanied with intellectual disability. Mutations in 17 genes have been ...shown to cause this phenotype. Recently, mutations in CIT, encoding CRIK (citron rho‐interacting kinase)—a component of the central spindle matrix—were added. We aimed at identifying novel MCPH‐associated genes and exploring their functional role in pathogenesis.
Methods
Linkage analysis and whole exome sequencing were performed in consanguineous and nonconsanguineous MCPH families to identify disease‐causing variants. Functional consequences were investigated by RNA studies and on the cellular level using immunofluorescence and microscopy.
Results
We identified homozygous mutations in KIF14 (NM_014875.2;c.263T>A;pLeu88*, c.2480_2482delTTG; p.Val827del, and c.4071G>A;p.Gln1357=) as the likely cause in 3 MCPH families. Furthermore, in a patient presenting with a severe form of primary microcephaly and short stature, we identified compound heterozygous missense mutations in KIF14 (NM_014875.2;c.2545C>G;p.His849Asp and c.3662G>T;p.Gly1221Val). Three of the 5 identified mutations impaired splicing, and 2 resulted in a truncated protein. Intriguingly, Kif14 knockout mice also showed primary microcephaly. Human kinesin‐like protein KIF14, a microtubule motor protein, localizes at the midbody to finalize cytokinesis by interacting with CRIK. We found impaired localization of both KIF14 and CRIK at the midbody in patient‐derived fibroblasts. Furthermore, we observed a large number of binucleated and apoptotic cells—signs of failed cytokinesis that we also observed in experimentally KIF14‐depleted cells.
Interpretation
Our data corroborate the role of an impaired cytokinesis in the etiology of primary and syndromic microcephaly, as has been proposed by recent findings on CIT mutations. Ann Neurol 2017;82:562–577
ABSTRACT
Introduction: Recessive mutations in the anoctamin‐5 gene (ANO5) cause a spectrum of clinical phenotypes, including limb‐girdle muscular dystrophy (LGMD 2L), distal myopathy, and ...asymptomatic hyperCKemia. Methods: In this report we describe our clinical, electrophysiological, pathological, and molecular findings in a subject with anoctaminopathy‐5. Results: A 49‐year‐old Arabic man from a consanguineous family presented with a 5‐year history of myalgias, hyperCKemia and an episode of unprovoked rhabdomyolysis. Muscle biopsy showed mild myopathic changes and interstitial amyloid deposition. ANO5 analysis detected a novel homozygous deletion of approximately 11.9 kb encompassing exons 13–17, predicted to be pathogenic. Conclusions: Anoctaminopathy‐5 can manifest with a phenotype reminiscent of metabolic myopathy and should be considered as a potential cause of myalgia and myoglobinuria. Amyloid deposition in the muscle biopsy is helpful for the diagnosis. A novel homozygous ANO5 deletion was identified, suggesting that screening for common mutations may have low yield in non‐European subjects. Muscle Nerve 50: 610–613, 2014
Hearing loss (HL) is the most common sensory disorder worldwide and genetic factors contribute to approximately half of congenital HL cases. HL is subject to extensive genetic heterogeneity, ...rendering molecular diagnosis difficult. Mutations of the transmembrane channel‐like 1 (TMC1) gene cause hearing defects in humans and mice. The precise function of TMC1 protein in the inner ear is unknown, although it is predicted to be involved in functional maturation of cochlear hair cells. TMC1 mutations result in autosomal recessive (DFNB7/11) and sometimes dominant (DFNA36) nonsyndromic HL. Mutations in TMC1 are responsible for a significant portion of HL, particularly in consanguineous populations. To evaluate the importance of TMC1 mutations in the Saudi population, we used a combination of autozygome‐guided candidate gene mutation analysis and targeted next generation sequencing in 366 families with HL previously shown to lack mutations in GJB2. We identified 12 families that carried five causative TMC1 mutations; including three novel (c.362+3A > G; c.758C > T p.Ser253Phe; c.1396_1398delACC p.Asn466del) and two reported mutations (c.100C > T p.Arg34Ter; c.1714G > A p.Asp572Asn). Each of the identified recessive mutation was classified as severe, by both age of onset and severity of HL. Similarly, consistent with the previously reported dominant variant p.Asp572Asn, the HL phenotype was progressive. Eight families in our cohort were found to share the pathogenic p.Arg34Ter mutation and linkage disequilibrium was observed between p.Arg34Ter and SNPs investigated. Our results indicate that TMC1 mutations account for about 3.3% (12/366) of Saudi HL cases and that the recurrent TMC1 mutation p.Arg34Ter is likely to be a founder mutation.
Vici syndrome is a recessively inherited multisystem disorder characterized by callosal agenesis, cataracts, cardiomyopathy, combined immunodeficiency and hypopigmentation. To investigate the ...molecular basis of Vici syndrome, we carried out exome and Sanger sequence analysis in a cohort of 18 affected individuals. We identified recessive mutations in EPG5 (previously KIAA1632), indicating a causative role in Vici syndrome. EPG5 is the human homolog of the metazoan-specific autophagy gene epg-5, encoding a key autophagy regulator (ectopic P-granules autophagy protein 5) implicated in the formation of autolysosomes. Further studies showed a severe block in autophagosomal clearance in muscle and fibroblasts from individuals with mutant EPG5, resulting in the accumulation of autophagic cargo in autophagosomes. These findings position Vici syndrome as a paradigm of human multisystem disorders associated with defective autophagy and suggest a fundamental role of the autophagy pathway in the immune system and the anatomical and functional formation of organs such as the brain and heart.
Abstract Background Autism spectrum disorder is characterized by social communicative deficits with restricted interests occurring in about 1% of the population. Although its exact cause is not ...known, several factors have been implicated in its etiology, including inborn errors of metabolism. Although relatively uncommon, these disorders frequently occur in countries with high rates of consanguinity and are often associated with behavioral problems, such as hyperactivity and aggression. The aim of this review is to examine the association of autism with these conditions. Method A computer-assisted search was performed to identify the most common inborn errors of metabolism associated with autism. Results The following disorders were identified: phenylketonuria, glucose-6-phosphatase deficiency, propionic acidemia, adenosine deaminase deficiency, Smith–Lemli–Opitz syndrome and mitochondrial disorders, and the recently described branched chain ketoacid dehydrogenase kinase deficiency. Conclusion The risk of autistic features is increased in children with inborn errors of metabolism, especially in the presence of cognitive and behavioral deficits. We propose that affected children should be screened for autism.
Pycnodysostosis is characterized by short stature, osteosclerosis, acro‐osteolysis, increased tendency of fractures, and distinctive dysmorphic features. It is a rare autosomal recessive disease ...caused by biallelic CTSK mutations. The clinical details of 18 patients from Saudi Arabia were reviewed. Short stature, osteopetrosis, acro‐osteolysis, and distinctive facial dysmorphism were documented in all cases. Our results highlight the significant complications associated with this disease. The large anterior fontanelle is one of the cardinal signs of this disease; however, half of our patients had small fontanelles and a quarter had craniosynostosis, which caused optic nerve compression. Sleep apnea was of the major complications in three patients. Bone fracture can be a presenting symptom, and in our patients it mainly occurred after the age of 3 years. Bone marrow suppression was seen in a single patient of our cohort who was misdiagnosed initially with malignant osteopetrosis. In this study, we also describe two novel (c.5G > A p.Trp2Ter, c.538G > A p.Gly180Ser) and two reported (c.244–29 A > G, c.830C > T p.Ala277Val) CTSK mutations. Our results indicate that the recurrent intronic variant, c.244–29 A > G is likely to be a founder mutation, as it was found in 78% (14/18 patients) of our cohort belonging to the same tribe.
Defects in the peroxisomes biogenesis and/or function result in peroxisomal disorders. In this study, we describe the largest Arab cohort to date (72 families) of clinically, biochemically and ...molecularly characterized patients with peroxisomal disorders. At the molecular level, we identified 43 disease‐causing variants, half of which are novel. The founder nature of many of the variants allowed us to calculate the minimum disease burden for these disorders in our population ~1:30 000, which is much higher than previous estimates in other populations. Clinically, we found an interesting trend toward genotype/phenotype correlation in terms of long‐term survival. Nearly half (40/75) of our peroxisomal disorders patients had documented survival beyond 1 year of age. Most unusual among the long‐term survivors was a multiplex family in which the affected members presented as adults with non‐specific intellectual disability and epilepsy. Other unusual presentations included the very recently described peroxisomal fatty acyl‐CoA reductase 1 disorder as well as CRD, spastic paraparesis, white matter (CRSPW) syndrome. We conclude that peroxisomal disorders are highly heterogeneous in their clinical presentation. Our data also confirm the demonstration that milder forms of Zellweger spectrum disorders cannot be ruled out by the “gold standard” very long chain fatty acids assay, which highlights the value of a genomics‐first approach in these cases.
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