De novo somatic mutations in components of the PI3K-AKT3-mTOR pathway cause hemimegalencephaly.

De novo somatic mutations in focal areas are well documented in diseases such as neoplasia but are rarely reported in malformation of the developing brain. Hemimegalencephaly (HME) is characterized by overgrowth of either one of the two cerebral hemispheres. The molecular etiology of HME remains a mystery.

Exome sequencing can improve diagnosis and alter patient management.

The translation of "next-generation" sequencing directly to the clinic is still being assessed but has the potential for genetic diseases to reduce costs, advance accuracy, and point to unsuspected yet treatable conditions. To study its capability in the clinic, we performed whole-exome sequencing in 118 probands with a diagnosis of a pediatric-onset neurodevelopmental disease in which most known causes had been excluded. Twenty-two genes not previously identified as disease-causing were identified in this study (19% of cohort), further establishing exome sequencing as a useful tool for gene discovery.

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

Background: We previously reported the existence of a unique autosomal recessive syndrome consisting of macrocephaly, multiple epiphyseal dysplasia and distinctive facial appearance mapping to chromosome 15q26.

Methods: In 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.

Results: Our analysis resulted in the identification of a homozygous p.

Whole exome sequencing identifies a splicing mutation in NSUN2 as a cause of a Dubowitz-like syndrome.

Background: Dubowitz syndrome (DS) is an autosomal recessive disorder characterized by the constellation of mild microcephaly, growth and mental retardation, eczema and peculiar facies. Over 140 cases have been reported, but the genetic basis is not understood.

Methods: We enrolled a multiplex consanguineous family from the United Arab Emirates with many of the key clinical features of DS as reported in previous series.

The very low density lipoprotein receptor-associated pontocerebellar hypoplasia and dysmorphic features in three Turkish patients.

Pontocerebellar hypoplasia consists of a rare heterogeneous group of congenital neurodevelopmental disorders characterized by hypoplasia and atrophy of the cerebellar cortex, dentate and pontine nuclei, and inferior olives. The very low density lipoprotein receptor protein is an integral part of the reelin signaling pathway, which guides neuroblast migration in the cerebral cortex and cerebellum. Mutations in this receptor cause nonprogressive cerebellar ataxia, mental retardation, and cerebellar hypoplasia.

Mutations in the glycosylphosphatidylinositol gene PIGL cause CHIME syndrome.

CHIME syndrome is characterized by colobomas, heart defects, ichthyosiform dermatosis, mental retardation (intellectual disability), and ear anomalies, including conductive hearing loss. Whole-exome sequencing on five previously reported cases identified PIGL, the de-N-acetylase required for glycosylphosphatidylinositol (GPI) anchor formation, as a strong candidate. Furthermore, cell lines derived from these cases had significantly reduced levels of the two GPI anchor markers, CD59 and a GPI-binding toxin, aerolysin (FLAER), confirming the pathogenicity of the mutations.

Evolutionarily assembled cis-regulatory module at a human ciliopathy locus.

Neighboring genes are often coordinately expressed within cis-regulatory modules, but evidence that nonparalogous genes share functions in mammals is lacking. Here, we report that mutation of either TMEM138 or TMEM216 causes a phenotypically indistinguishable human ciliopathy, Joubert syndrome. Despite a lack of sequence homology, the genes are aligned in a head-to-tail configuration and joined by chromosomal rearrangement at the amphibian-to-reptile evolutionary transition.

CEP41 is mutated in Joubert syndrome and is required for tubulin glutamylation at the cilium.

Tubulin glutamylation is a post-translational modification that occurs predominantly in the ciliary axoneme and has been suggested to be important for ciliary function. However, its relationship to disorders of the primary cilium, termed ciliopathies, has not been explored. Here we mapped a new locus for Joubert syndrome (JBTS), which we have designated as JBTS15, and identified causative mutations in CEP41, which encodes a 41-kDa centrosomal protein.

Co-occurrence of distinct ciliopathy diseases in single families suggests genetic modifiers.

Disorders within the "ciliopathy" spectrum include Joubert (JS), Bardet-Biedl syndromes (BBS), and nephronophthisis (NPHP). Although mutations in single ciliopathy genes can lead to these different syndromes between families, there have been no reports of phenotypic discordance within a single family. We report on two consanguineous families with discordant ciliopathies in sibling.

New recessive syndrome of microcephaly, cerebellar hypoplasia, and congenital heart conduction defect.

We identified a two-branch consanguineous family in which four affected members (three females and one male) presented with constitutive growth delay, severe psychomotor retardation, microcephaly, cerebellar hypoplasia, and second-degree heart block. They also shared distinct facial features and similar appearance of their hands and feet. Childhood-onset insulin-dependent diabetes mellitus developed in one affected child around the age of 9 years.

Modeling human disease in humans: the ciliopathies.

Soon, the genetic basis of most human Mendelian diseases will be solved. The next challenge will be to leverage this information to uncover basic mechanisms of disease and develop new therapies. To understand how this transformation is already beginning to unfold, we focus on the ciliopathies, a class of multi-organ diseases caused by disruption of the primary cilium.

A systems-biology approach to understanding the ciliopathy disorders.

'Ciliopathies' are an emerging class of genetic multisystemic human disorders that are caused by a multitude of largely unrelated genes that affect ciliary structure/function. They are unified by shared clinical features, such as mental retardation, cystic kidney, retinal defects and polydactyly, and by the common localization of the protein products of these genes at or near the primary cilium of cells. With the realization that many previously disparate conditions are a part of this spectrum of disorders, there has been tremendous interest in the function of cilia in developmental signaling and homeostasis.

Faulty initiation of proteoglycan synthesis causes cardiac and joint defects.

Proteoglycans are a major component of extracellular matrix and contribute to normal embryonic and postnatal development by ensuring tissue stability and signaling functions. We studied five patients with recessive joint dislocations and congenital heart defects, including bicuspid aortic valve (BAV) and aortic root dilatation. We identified linkage to chromosome 11 and detected a mutation (c.

The ciliopathies in neuronal development: a clinical approach to investigation of Joubert syndrome and Joubert syndrome-related disorders.

A group of disorders with disparate symptomatology, including congenital cerebellar ataxia, retinal blindness, liver fibrosis, polycystic kidney disease, and polydactyly, have recently been united under a single disease mechanism called 'ciliopathies'. The ciliopathies are due to defects of the cellular antenna known as the primary cilium, a microtubule-based extension of cellular membranes found in nearly all cell types. Key among these ciliopathies is Joubert syndrome, displaying ataxia, oculomotor apraxia, and mental retardation* with a pathognomonic 'molar tooth sign' on brain magnetic resonance imaging.

Defective Wnt-dependent cerebellar midline fusion in a mouse model of Joubert syndrome.

The ciliopathy Joubert syndrome is marked by cerebellar vermis hypoplasia, a phenotype for which the pathogenic mechanism is unclear. To investigate Joubert syndrome pathogenesis, we have examined mice with mutated Ahi1, the first identified Joubert syndrome-associated gene. These mice show cerebellar hypoplasia with a vermis-midline fusion defect early in development.

Subcellular spatial regulation of canonical Wnt signalling at the primary cilium.

Mechanisms of signal transduction regulation remain a fundamental question in a variety of biological processes and diseases. Previous evidence indicates that the primary cilium can act as a signalling hub, but its exact role in many of the described pathways has remained elusive. Here, we investigate the mechanism of cilia-mediated regulation of the canonical Wnt pathway.

Cilia in the nervous system: linking cilia function and neurodevelopmental disorders.

Purpose Of Review: Ciliopathies are genetic disorders caused by defects of primary ciliary structure and/or function and are characterized by pleiotropic clinical features. The ciliopathies include several partially overlapping syndromes such as Joubert syndrome, Bardet-Biedl syndrome and Meckel-Gruber syndrome, all of which have pronounced neurodevelopmental features. Here we focus on potential roles of cilia in central nervous system function, to explore how impairments may cause brain malformation and neurodevelopmental disease.

Simultaneous multiple-excitation multiphoton microscopy yields increased imaging sensitivity and specificity.

Background: Multiphoton microscopy (MPM) offers many advantages over conventional wide-field and confocal laser scanning microscopy (CLSM) for imaging biological samples such as 3D resolution of excitation, reduced phototoxicity, and deeper tissue imaging. However, adapting MPM for critical multi-color measurements presents a challenge because of the largely overlapping two-photon absorption (TPA) peaks of common biological fluorophores. Currently, most multi-color MPM relies on the absorbance at one intermediate wavelength of multiple dyes, which introduces problems such as decreased and unequal excitation efficiency across the set of dyes.

TTC21B contributes both causal and modifying alleles across the ciliopathy spectrum.

Ciliary dysfunction leads to a broad range of overlapping phenotypes, collectively termed ciliopathies. This grouping is underscored by genetic overlap, where causal genes can also contribute modifier alleles to clinically distinct disorders. Here we show that mutations in TTC21B, which encodes the retrograde intraflagellar transport protein IFT139, cause both isolated nephronophthisis and syndromic Jeune asphyxiating thoracic dystrophy.

Genetic regulation of human brain development: lessons from Mendelian diseases.

One of the fundamental goals in human genetics is to link gene function to phenotype, yet the function of the majority of the genes in the human body is still poorly understood. This is especially true for the developing human brain. The study of human phenotypes that result from inherited, mutated alleles is the most direct evidence for the requirement of a gene in human physiology.

Expanding the clinical spectrum of SPG11 gene mutations in recessive hereditary spastic paraplegia with thin corpus callosum.

Hereditary spastic paraplegia (HSP) represents a large group of neurological disorders characterized by progressive spasticity of the lower limbs. One subtype of HSP shows an autosomal recessive form of inheritance with thin corpus callosum (ARHSP-TCC), and displays genetic heterogeneity with four known loci. We identified a consanguineous Egyptian family with five affected individuals with ARHSP-TCC.

A novel cerebello-ocular syndrome with abnormal glycosylation due to abnormalities in dolichol metabolism.

Cerebellar hypoplasia and slowly progressive ophthalmological symptoms are common features in patients with congenital disorders of glycosylation type I. In a group of patients with congenital disorders of glycosylation type I with unknown aetiology, we have previously described a distinct phenotype with severe, early visual impairment and variable eye malformations, including optic nerve hypoplasia, retinal coloboma, congenital cataract and glaucoma. Some of the symptoms overlapped with the phenotype in other congenital disorders of glycosylation type I subtypes, such as vermis hypoplasia, anaemia, ichtyosiform dermatitis, liver dysfunction and coagulation abnormalities.

SRD5A3 is required for converting polyprenol to dolichol and is mutated in a congenital glycosylation disorder.

N-linked glycosylation is the most frequent modification of secreted and membrane-bound proteins in eukaryotic cells, disruption of which is the basis of the congenital disorders of glycosylation (CDGs). We describe a new type of CDG caused by mutations in the steroid 5alpha-reductase type 3 (SRD5A3) gene. Patients have mental retardation and ophthalmologic and cerebellar defects.

Cystic kidney disease: the role of Wnt signaling.

Wnt signaling encompasses a variety of signaling cascades that can be activated by secreted Wnt ligands. Two such pathways, the canonical or beta-catenin pathway and the planar cell polarity (PCP) pathway, have recently received attention for their roles in multiple cellular processes within the kidney. Both of these pathways are important for kidney development as well as homeostasis and injury repair.