Recessive ARFGEF2 mutation causes progressive microcephaly, epilepsy, and a distinct MRI pattern

Background: Periventricular nodular heterotopia, a common form of neuronal heterotopia, is heterogeneous in etiology. Recessive mutations in ARFGEF2 causing microcephaly and periventricular heterotopia have rarely been reported. Case Presentation: We report two Saudi siblings with a homozygous ARFGEF2 mutation (c.958 + 1G > A) presenting with microcephaly, dyskinetic movements, seizures, and a distinct brain magnetic resonance imaging pattern, describing the genotype and radiology phenotype correlation. Conclusion: We speculate that the involvement of the putamen may be a key under recognized feature of ARFGEF2 mutations. [JBCGenetics 2018; 1(1.000): 40-42

An atypical presentation of severe congenital contractures and lack of cerebellar involvement in a patient with a novel LAMA1 mutation

Background: LAMA1 gene is mutated in patients with Poretti-Boltshauser syndrome, which include mainly the characteristic neuroimaging findings of cerebellar dysplasia and cysts. Case Presentation: We present a novel homozygous LAMA1 variant that is predicted to cause atypical phenotype of severe arthrogryposis, feeding difficulties, developmental delay, retinopathy, and no cerebellar involvement. Conclusion: Our findings are suggestive of absence of cerebellar involvement in LAMA1 mutations in some cases and phenotype may include severe arthrogryposis. [JBCGenetics 2018; 1(1.000): 43-46

CPAP promotes timely cilium disassembly to maintain neural progenitor pool

A mutation in the centrosomal-P4.1-associated protein (CPAP) causes Seckel syndrome with microcephaly, which is suggested to arise from a decline in neural progenitor cells (NPCs) during development. However, mechanisms of NPCs maintenance remain unclear. Here, we report an unexpected role for the cilium in NPCs maintenance and identify CPAP as a negative regulator of ciliary length independent of its role in centrosome biogenesis. At the onset of cilium disassembly, CPAP provides a scaffold for the cilium disassembly complex (CDC), which includes Nde1, Aurora A, and OFD1, recruited to the ciliary base for timely cilium disassembly. In contrast, mutated CPAP fails to localize at the ciliary base associated with inefficient CDC recruitment, long cilia, retarded cilium disassembly, and delayed cell cycle re-entry leading to premature differentiation of patient iPS-derived NPCs. Aberrant CDC function also promotes premature differentiation of NPCs in Seckel iPS-derived organoids. Thus, our results suggest a role for cilia in microcephaly and its involvement during neurogenesis and brain size control

In search of triallelism in Bardet–Biedl syndrome

Bardet–Biedl syndrome (BBS) is a model disease for ciliopathy in humans. The remarkable genetic heterogeneity that characterizes this disease is consistent with accumulating data on the interaction between the proteins encoded by the 14 BBS genes identified to date. Previous reports suggested that such interaction may also extend to instances of oligogenic inheritance in the form of triallelism which defies the long held view of BBS as an autosomal recessive disease. In order to investigate the magnitude of triallelism in BBS, we conducted a comprehensive analysis of all 14 BBS genes as well as the CCDC28B-modifier gene in a cohort of 29 BBS families, most of which are multiplex. Two in trans mutations in a BBS gene were identified in each of these families for a total of 20 mutations including 12 that are novel. In no instance did we observe two mutations in unaffected members of a given family, or observe the presence of a third allele that convincingly acted as a modifier of penetrance and supported the triallelic model of BBS. In addition to presenting a comprehensive genotype/phenotype overview of a large set of BBS mutations, including the occurrence of nonsyndromic retinitis pigmentosa in a family with a novel BBS9 mutation, our study argues in favor of straightforward autosomal recessive BBS in most cases

Biallelic variants in PCDHGC4 cause a novel neurodevelopmental syndrome with progressive microcephaly, seizures, and joint anomalies

Purpose We aimed to define a novel autosomal recessive neurodevelopmental disorder, characterize its clinical features, and identify the underlying genetic cause for this condition. Methods We performed a detailed clinical characterization of 19 individuals from nine unrelated, consanguineous families with a neurodevelopmental disorder. We used genome/exome sequencing approaches, linkage and cosegregation analyses to identify disease-causing variants, and we performed three-dimensional molecular in silico analysis to predict causality of variants where applicable. Results In all affected individuals who presented with a neurodevelopmental syndrome with progressive microcephaly, seizures, and intellectual disability we identified biallelic disease-causing variants in Protocadherin-gamma-C4 (PCDHGC4). Five variants were predicted to induce premature protein truncation leading to a loss of PCDHGC4 function. The three detected missense variants were located in extracellular cadherin (EC) domains EC5 and EC6 of PCDHGC4, and in silico analysis of the affected residues showed that two of these substitutions were predicted to influence the Ca2+-binding affinity, which is essential for multimerization of the protein, whereas the third missense variant directly influenced the cis-dimerization interface of PCDHGC4. Conclusion We show that biallelic variants in PCDHGC4 are causing a novel autosomal recessive neurodevelopmental disorder and link PCDHGC4 as a member of the clustered PCDH family to a Mendelian disorder in humans