Summary Despite significant heritability of autism spectrum disorders (ASDs), their extreme genetic heterogeneity has proven challenging for gene discovery. Studies of primarily simplex families have implicated de novo copy number changes and point mutations, but are not optimally designed to identify inherited risk alleles. We apply whole exome sequencing (WES) to ASD families enriched for inherited causes due to consanguinity and find familial ASD associated with biallelic mutations in disease genes (AMT, PEX7, SYNE1, VPS13B, PAH, POMGNT1), some implicated for the first time in ASD. At least some of these genes show biallelic mutations in nonconsanguineous families as well. These mutations are often only partially disabling or present atypically, with patients lacking diagnostic features of the Mendelian disorders with which these genes are classically associated. Our study shows the utility of WES for identifying specific genetic conditions not clinically suspected and the importance of partial loss of gene function in ASDs.

Pediatric-onset ataxias often present clinically with developmental delay and intellectual disability, with prominent cerebellar atrophy as a key neuroradiographic finding. Here we describe a novel clinically distinguishable recessive syndrome in 12 families with cerebellar atrophy together with ataxia, coarsened facial features and intellectual disability, due to truncating mutations in sorting nexin 14 (SNX14), encoding a ubiquitously expressed modular PX-domain-containing sorting factor. We found SNX14 localized to lysosomes, and associated with phosphatidyl-inositol (3,5)P2, a key component of late endosomes/lysosomes. Patient cells showed engorged lysosomes and slower autophagosome clearance rate upon starvation induction. Zebrafish morphants showed dramatic loss of cerebellar parenchyma, accumulated autophagosomes, and activation of apoptosis. Our results suggest a unique ataxia syndrome due to biallelic SNX14 mutations, leading to lysosome-autophagosome dysfunction.

Glycosphingolipids are ubiquitous constituents of eukaryotic plasma membranes, and their sialylated derivatives, gangliosides, are the major class of glycoconjugates expressed by neurons. Deficiencies in their catabolic pathways give rise to a large and well-studied group of inherited disorders, the lysosomal storage diseases. Although many glycosphingolipid catabolic defects have been defined, only one proven inherited disease arising from a defect in ganglioside biosynthesis is known. This disease, because of defects in the first step of ganglioside biosynthesis (GM3 synthase), results in a severe epileptic disorder found at high frequency amongst the Old Order Amish. Here we investigated an unusual neurodegenerative phenotype, most commonly classified as a complex form of hereditary spastic paraplegia, present in families from Kuwait, Italy and the Old Order Amish. Our genetic studies identified mutations in B4GALNT1 (GM2 synthase), encoding the enzyme that catalyzes the second step in complex ganglioside biosynthesis, as the cause of this neurodegenerative phenotype. Biochemical profiling of glycosphingolipid biosynthesis confirmed a lack of GM2 in affected subjects in association with a predictable increase in levels of its precursor, GM3, a finding that will greatly facilitate diagnosis of this condition. With the description of two neurological human diseases involving defects in two sequentially acting enzymes in ganglioside biosynthesis, there is the real possibility that a previously unidentified family of ganglioside deficiency diseases exist. The study of patients and animal models of these disorders will pave the way for a greater understanding of the role gangliosides play in neuronal structure and function and provide insights into the development of effective treatment therapies.

Joubert Syndrome Related Disorders (JSRDs) are autosomal recessive pleiotropic conditions sharing a peculiar cerebellar and brainstem malformation known as the "molar tooth sign" (MTS). Recently, mutations in a novel ciliary gene, RPGRIP1L, have been shown to cause both JSRDs and MeckelGruber syndrome. We searched for RPGRIP1L mutations in 120 patients with proven MTS and phenotypes representative of all JSRD clinical subgroups. Two homozygous mutations, the previously reported p.T615P in exon 15 and the novel c.2268_2269delA in exon 16, were detected in two out of 16 families with cerebello-renal presentation (~12%). Conversely, no pathogenic changes were found in patients with other JSRD phenotypes, suggesting that RPGRIP1L mutations are largely confined to the cerebello-renal subgroup, while they overall represent a rare cause of JSRD (<2%).

We studied 21 patients with Sanjad-Sakati syndrome (SSS) from 16 families. Parental consanguinity was recorded in 2 families (12.5%). All patients had severe intrauterine growth retardation, short stature, small hands and feet, blue sclera, deep-set eyes, microcephaly, persistent hypocalcaemia and hypoparathyroidism. Medullary stenosis was detected in 2 patients. Cytogenetic and fluorescent in situ hybridization studies were normal. All affected persons had homozygous deletion of 12 bp (155-166del) in exon 3 of the TBCE gene. All of the parents were heterozygous carriers of this mutation. The high frequency of SSS and low frequency of consanguineous marriages in this study may reflect a high rate of heterozygous carriers. ‫الكويت‬ ‫يف‬ ‫حالة‬