Bi-allelic PRRT2 variants may predispose to Self-limited Familial Infantile Epilepsy.

Heterozygous PRRT2 variants are frequently implicated in Self-limited Infantile Epilepsy, whereas homozygous variants are so far linked to severe presentations including developmental and epileptic encephalopathy, movement disorders, and intellectual disability. In a study aiming to explore the genetics of epilepsy in the Sudanese population, we investigated several families including a consanguineous family with three siblings diagnosed with self-limited infantile epilepsy. We evaluated both dominant and recessive inheritance using whole exome sequencing and genomic arrays. We identified a pathogenic homozygous splice-site variant in the first intron of PRRT2 [NC_000016.10(NM_145239.3):c.-65-1G > A] that segregated with the phenotype in this family. This work taps into the genetics of epilepsy in an underrepresented African population and suggests that the phenotypes of homozygous PRRT2 variants may include milder epilepsy presentations without movement disorders.

Clinical phenotyping and genetic diagnosis of a large cohort of Sudanese families with hereditary spinocerebellar degenerations.

Hereditary spinocerebellar degenerations (SCDs) is an umbrella term that covers a group of monogenic conditions that share common pathogenic mechanisms and include hereditary spastic paraplegia (HSP), cerebellar ataxia, and spinocerebellar ataxia. They are often complicated with axonal neuropathy and/or intellectual impairment and overlap with many neurological conditions, including neurodevelopmental disorders. More than 200 genes and loci inherited through all modes of Mendelian inheritance are known. Autosomal recessive inheritance predominates in consanguineous communities; however, autosomal dominant and X-linked inheritance can also occur. Sudan is inhabited by genetically diverse populations, yet it has high consanguinity rates. We used next-generation sequencing, genotyping, bioinformatics analysis, and candidate gene approaches to study 90 affected patients from 38 unrelated Sudanese families segregating multiple forms of SCDs. The age-at-onset in our cohort ranged from birth to 35 years; however, most patients manifested childhood-onset diseases (the mean and median ages at onset were 7.5 and 3 years, respectively). We reached the genetic diagnosis in 63% and possibly up to 73% of the studied families when considering variants of unknown significance. Combining the present data with our previous analysis of 25 Sudanese HSP families, the success rate reached 52-59% (31-35/59 families). In this article we report candidate variants in genes previously known to be associated with SCDs or other phenotypically related monogenic disorders. We also highlight the genetic and clinical heterogeneity of SCDs in Sudan, as we did not identify a major causative gene in our cohort, and the potential for discovering novel SCD genes in this population.

Pathogenic Variants in ABHD16A Cause a Novel Psychomotor Developmental Disorder With Spastic Paraplegia.

Introduction: Hereditary spastic paraplegia is a clinically and genetically heterogeneous neurological entity that includes more than 80 disorders which share lower limb spasticity as a common feature. Abnormalities in multiple cellular processes are implicated in their pathogenesis, including lipid metabolism; but still 40% of the patients are undiagnosed. Our goal was to identify the disease-causing variants in Sudanese families excluded for known genetic causes and describe a novel clinico-genetic entity. Methods: We studied four patients from two unrelated consanguineous Sudanese families who manifested a neurological phenotype characterized by spasticity, psychomotor developmental delay and/or regression, and intellectual impairment. We applied next-generation sequencing, bioinformatics analysis, and Sanger sequencing to identify the genetic culprit. We then explored the consequences of the identified variants in patients-derived fibroblasts using targeted-lipidomics strategies. Results and Discussion: Two homozygous variants in ABHD16A segregated with the disease in the two studied families. ABHD16A encodes the main brain phosphatidylserine hydrolase. In vitro, we confirmed that ABHD16A loss of function reduces the levels of certain long-chain lysophosphatidylserine species while increases the levels of multiple phosphatidylserine species in patient's fibroblasts. Conclusion: ABHD16A loss of function is implicated in the pathogenesis of a novel form of complex hereditary spastic paraplegia.

Bypassing ubiquitination enables LAT recycling to the cell surface and enhanced signaling in T cells.

LAT molecules defective in ubiquitination have an increased half-life and induce enhanced signaling when expressed in T cells. In this study, we have examined the role of ubiquitination in regulating LAT endocytosis, recycling, and degradation in resting and stimulated T cells. By tracking and comparing plasma membrane-labeled wild type and ubiquitination-resistant 2KR LAT, we find that ubiquitination promotes the degradation of surface LAT in T cells. Activation of T cells increases LAT ubiquitination and promotes trafficking of internalized LAT to lysosomes for degradation. Ubiquitination of LAT does not change internalization rates from the cell surface, but prevents efficient recycling of LAT to the surface of T cells. Our study demonstrates that surface LAT levels are tightly controlled by ubiquitination. LAT in unstimulated cells lacks ubiquitin allowing for increased LAT stability and efficient T cell activation upon TCR triggering; ubiquitination leads to efficient removal of LAT after activation.

Hereditary spastic paraplegias: identification of a novel SPG57 variant affecting TFG oligomerization and description of HSP subtypes in Sudan.

Hereditary spastic paraplegias (HSP) are the second most common type of motor neuron disease recognized worldwide. We investigated a total of 25 consanguineous families from Sudan. We used next-generation sequencing to screen 74 HSP-related genes in 23 families. Linkage analysis and candidate gene sequencing was performed in two other families. We established a genetic diagnosis in six families with autosomal recessive HSP (SPG11 in three families and TFG/SPG57, SACS and ALS2 in one family each). A heterozygous mutation in a gene involved in an autosomal dominant HSP (ATL1/SPG3A) was also identified in one additional family. Six out of seven identified variants were novel. The c.64C>T (p.(Arg22Trp)) TFG/SPG57 variant (PB1 domain) is the second identified that underlies HSP, and we demonstrated its impact on TFG oligomerization in vitro. Patients did not present with visual impairment as observed in a previously reported SPG57 family (c.316C>T (p.(Arg106Cys)) in coiled-coil domain), suggesting unique contributions of the PB1 and coiled-coil domains in TFG complex formation/function and a possible phenotype correlation to variant location. Some families manifested marked phenotypic variations implying the possibility of modifier factors complicated by high inbreeding. Finally, additional genetic heterogeneity is expected in HSP Sudanese families. The remaining families might unravel new genes or uncommon modes of inheritance.

A screen to identify cellular modulators of soluble levels of an amyotrophic lateral sclerosis (ALS)-causing mutant SOD1.

The molecular pathology of many protein misfolding, toxic gain-of-function diseases, such as amyotrophic lateral sclerosis (ALS), is not well understood. Although protein misfolding and aggregation are common themes in these diseases, efforts to identify cellular factors that regulate this process in an unbiased fashion and on a global scale have been lacking. Using an adapted version of an extant ß-gal-based protein solubility assay, an expression screen for cellular modulators of solubility of an ALS-causing mutant SOD1 was carried out in mammalian cells. Following fluorescence-activated cell sorting enrichment of a mouse spinal cord cDNA library for gene products that increased SOD1 solubility, high-throughput screening of the cDNA pools from this enriched fraction was employed to identify pools containing relevant modulators. Positive pools, containing approximately 10 cDNA clones each, were diluted and rescreened iteratively until individual clones that improved SOD1 folding/solubility were identified. Genes with profound effects in the solubility assay were selected for validation by independent biochemical assays. Six of 10 validated genes had a significant effect on SOD1 solubility and folding in a SOD1 promoter-driven ß-gal assay, indicating that global screening of cellular targets using such protein solubility/folding assay is viable and can be adapted for other misfolding diseases.