The main familial focal epilepsies of childhood are autosomal dominant nocturnal frontal lobe epilepsy, familial temporal lobe epilepsy and familial focal epilepsy with variable foci. A frameshift mutation in the DEPDC5 (DEP domain containing protein 5) gene was identified in a family with focal epilepsy with variable foci, by linkage analysis and exome sequencing. Subsequent pyrosequencing of DEPDC5 in a cohort of 15 additional families with focal epilepsies revealed four nonsense and one missense mutations. Our findings provided evidence for frequent (37%) loss-of-function mutations in DEPDC5 associated with a broad spectrum of focal epilepsies. The implication of a DEP domain (Dishevelled, Egl-10 and Pleckstrin domain)-containing protein that may be involved in membrane trafficking and/or G-protein signaling, opens new avenues for research.

We have identified a novel gene in a genome-wide, double-strand break DNA repair RNAi screen and show that is involved in the neurological disease hereditary spastic paraplegia.

Spastic paraplegia 46 refers to a locus mapped to chromosome 9 that accounts for a complicated autosomal-recessive form of hereditary spastic paraplegia (HSP). With next-generation sequencing in three independent families, we identified four different mutations in GBA2 (three truncating variants and one missense variant), which were found to cosegregate with the disease and were absent in controls. GBA2 encodes a microsomal nonlysosomal glucosylceramidase that catalyzes the conversion of glucosylceramide to free glucose and ceramide and the hydrolysis of bile acid 3-O-glucosides. The missense variant was also found at the homozygous state in a simplex subject in whom no residual glucocerebrosidase activity of GBA2 could be evidenced in blood cells, opening the way to a possible measurement of this enzyme activity in clinical practice. The overall phenotype was a complex HSP with mental impairment, cataract, and hypogonadism in males associated with various degrees of corpus callosum and cerebellar atrophy on brain imaging. Antisense morpholino oligonucleotides targeting the zebrafish GBA2 orthologous gene led to abnormal motor behavior and axonal shortening/branching of motoneurons that were rescued by the human wild-type mRNA but not by applying the same mRNA containing the missense mutation. This study highlights the role of ceramide metabolism in HSP pathology.

Objective To identify the causative gene in SCA22, an autosomal dominant cerebellar ataxia mapped to chromosome 1p21-q23. Subjects and Methods We previously characterized a large Chinese family with progressive ataxia designated SCA22, which overlaps with the locus of SCA19. The disease locus in a French family and an Ashkenazi Jewish American family was also mapped to this region. Members from all three families were enrolled. Whole exome sequencing was performed to identify candidate mutations, which were narrowed by linkage analysis and confirmed by Sanger sequencing and co-segregation analyses. Mutational analyses were also performed in 105 Chinese and 55 Japanese families with cerebellar ataxia. Mutant gene products were examined in a heterologous expression system to address the changes in protein localization and electrophysiological functions. Results We identified heterozygous mutations in the voltage-gated potassium channel Kv4.3-encoding gene KCND3: an in-frame three-nucleotide deletion c.679_681delTTC p.F227del in both the Chinese and French pedigrees, and a missense mutation c.1034G>T p.G345V in the Ashkenazi Jewish family. Direct sequencing of KCND3 further identified three mutations, c.1034G>T p.G345V, c.1013T>C p.V338E and c.1130C>T p.T377M, in three Japanese kindreds. Immunofluorescence analyses revealed that the mutant p.F227del Kv4.3 subunits were retained in the cytoplasm, consistent with the lack of A-type K+ channel conductance in whole-cell patch-clamp recordings. Interpretation Our data identify the cause of SCA19/22 in patients of diverse ethnic origins as mutations in KCND3. These findings further emphasize the important role of ion channels as key regulators of neuronal excitability in the pathogenesis of cerebellar degeneration.

Hereditary spastic paraplegias (HSP) constitute a heterogeneous group of neurodegenerative disorders characterized by slowly progressive spasticity of the lower extremities. Only a few different mutations in the SPG10 gene, KIF5A, have been described in pure dominant forms of the disease. We sequenced the motor domain of KIF5A in a large panel of 205 European HSP patients with either pure or complicated forms of the disease. We identified eight different heterozygous missense mutations, seven novels, in eight different families of French origin. Residue R280 was a mutational hot spot. Interestingly, the patients in 7/8 families had a complex phenotype, with peripheral neuropathy, severe upper limb amyotrophy (Silver syndrome-like), mental impairment, parkinsonism, deafness and/or retinitis pigmentosa as variably associated features. We report the largest series of SPG10 families described so far, which extends both the mutational spectrum of the disease and its phenotype, which now includes complicated forms of HSP. SPG10 mutations were found in 10% of our complicated forms of HSP, suggesting that mutations in KIF5A represent the major cause of complicated AD-HSP in France.

DEPDC5 loss-of-function mutations were found in 13% of the families with a presentation of ADNFLE. The rate of drug resistance was high in patients with DEPDC5 mutations. Small ADNFLE pedigrees with DEPDC5 mutations might actually represent a part of the broader familial focal epilepsy with variable foci phenotype.

The hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterised by progressive spasticity in the lower limbs. The nosology of autosomal recessive forms is complex as most mapped loci have been identified in only one or a few families and account for only a small percentage of patients. We used next-generation sequencing focused on the SPG30 chromosomal region on chromosome 2q37.3 in two patients from the original linked family. In addition, wide genome scan and candidate gene analysis were performed in a second family of Palestinian origin. We identified a single homozygous mutation, p.R350G, that was found to cosegregate with the disease in the SPG30 kindred and was absent in 970 control chromosomes while affecting a strongly conserved amino acid at the end of the motor domain of KIF1A. Homozygosity and linkage mapping followed by mutation screening of KIF1A allowed us to identify a second mutation, p.A255V, in the second family. Comparison of the clinical features with the nature of the mutations of all reported KIF1A families, including those reported recently with hereditary sensory and autonomic neuropathy, suggests phenotypegenotype correlations that may help to understand the mechanisms involved in motor neuron degeneration. We have shown that mutations in the KIF1A gene are responsible for SPG30 in two autosomal recessive HSP families. In published families, the nature of the KIF1A mutations seems to be of good predictor of the underlying phenotype and vice versa. INTRODUCTIONThe hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of neurodegenerative diseases characterised by progressive spasticity in the lower limbs. 1 The mode of inheritance may be autosomal dominant, autosomal recessive (ARHSP) or X-linked. More than 48 different loci (SPGn) have been mapped so far, and 23 responsible genes identified. The corresponding proteins are often involved in intracellular trafficking or mitochondrial functions. 2,3 Clinically, one can distinguish between pure and complicated forms of HSP. 1,2 Pure forms consist of isolated pyramidal signs, such as spasticity, abnormal reflexes (brisk reflexes and Babinski sign) and motor deficit, often associated with sphincter disturbances and deep sensory loss. In the complicated forms of HSP the disease is variably associated with numerous combinations of neurological and extraneurological signs, such as cerebellar ataxia, dysarthria, mental retardation, peripheral neuropathy, optic atrophy, retinitis pigmentosa and/or hearing loss, which may be accompanied by abnormal brain MRI (atrophy of the cortex, cerebellum or corpus callosum, white matter abnormalities, etc).Mutations in the KIF1A gene (MIM 601255) were very recently described in two different clinically and genetically heterogeneous groups of neurodegenerative diseases. 4,5 In hereditary sensory and autonomic neuropathy (HSAN), all patients from four families with different origins shared a common hom...

Hereditary spastic paraplegias (HSPs) form a heterogeneous group of neurological disorders. A whole-genome linkage mapping effort was made with three HSP-affected families from Spain, Portugal, and Tunisia and it allowed us to reduce the SPG26 locus interval from 34 to 9 Mb. Subsequently, a targeted capture was made to sequence the entire exome of affected individuals from these three families, as well as from two additional autosomal-recessive HSP-affected families of German and Brazilian origins. Five homozygous truncating (n = 3) and missense (n = 2) mutations were identified in B4GALNT1. After this finding, we analyzed the entire coding region of this gene in 65 additional cases, and three mutations were identified in two subjects. All mutated cases presented an early-onset spastic paraplegia, with frequent intellectual disability, cerebellar ataxia, and peripheral neuropathy as well as cortical atrophy and white matter hyperintensities on brain imaging. B4GALNT1 encodes β-1,4-N-acetyl-galactosaminyl transferase 1 (B4GALNT1), involved in ganglioside biosynthesis. These findings confirm the increasing interest of lipid metabolism in HSPs. Interestingly, although the catabolism of gangliosides is implicated in a variety of neurological diseases, SPG26 is only the second human disease involving defects of their biosynthesis.