An immune-mediated inflammatory process may play a role in PVL. TNFalpha, a myelinotoxic factor, may be the major mediator.

In this study, we report the experience of the only reference clinical next-generation sequencing lab in Saudi Arabia with the first 1000 families who span a wide-range of suspected Mendelian phenotypes. A total of 1019 tests were performed in the period of March 2016–December 2016 comprising 972 solo (index only), 14 duo (parents or affected siblings only), and 33 trio (index and parents). Multigene panels accounted for 672 tests, while whole exome sequencing (WES) represented the remaining 347 tests. Pathogenic or likely pathogenic variants that explain the clinical indications were identified in 34% (27% in panels and 43% in exomes), spanning 279 genes and including 165 novel variants. While recessive mutations dominated the landscape of solved cases (71% of mutations, and 97% of which are homozygous), a substantial minority (27%) were solved on the basis of dominant mutations. The highly consanguineous nature of the study population also facilitated homozygosity for many private mutations (only 32.5% of the recessive mutations are founder), as well as the first instances of recessive inheritance of previously assumed strictly dominant disorders (involving ITPR1, VAMP1, MCTP2, and TBP). Surprisingly, however, dual molecular diagnosis was only observed in 1.5% of cases. Finally, we have encountered candidate variants in 75 genes (ABHD6, ACY3, ADGRB2, ADGRG7, AGTPBP1, AHNAK2, AKAP6, ASB3, ATXN1L, C17orf62, CABP1, CCDC186, CCP110, CLSTN2, CNTN3, CNTN5, CTNNA2, CWC22, DMAP1, DMKN, DMXL1, DSCAM, DVL2, ECI1, EP400, EPB41L5, FBXL22, GAP43, GEMIN7, GIT1, GRIK4, GRSF1, GTRP1, HID1, IFNL1, KCNC4, LRRC52, MAP7D3, MCTP2, MED26, MPP7, MRPS35, MTDH, MTMR9, NECAP2, NPAT, NRAP, PAX7, PCNX, PLCH2, PLEKHF1, PTPN12, QKI, RILPL2, RIMKLA, RIMS2, RNF213, ROBO1, SEC16A, SIAH1, SIRT2, SLAIN2, SLC22A20, SMDT1, SRRT, SSTR1, ST20, SYT9, TSPAN6, UBR4, VAMP4, VPS36, WDR59, WDYHV1, and WHSC1) not previously linked to human phenotypes and these are presented to accelerate post-publication matchmaking. Two of these genes were independently mutated in more than one family with similar phenotypes, which substantiates their link to human disease (AKAP6 in intellectual disability and UBR4 in early dementia). If the novel candidate disease genes in this cohort are independently confirmed, the yield of WES will have increased to 83%, which suggests that most “negative” clinical exome tests are unsolved due to interpretation rather than technical limitations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00439-017-1821-8) contains supplementary material, which is available to authorized users.

The purpose of this study was to identify the biochemical and genetic defect in L-2-hydroxyglutaric aciduria, a neurometabolic disorder characterized by the presence of elevated concentrations of L-2-hydroxyglutaric acid in urine, plasma, and cerebrospinal fluid. Evidence is provided for the existence in rat tissues of a FAD-dependent enzyme catalyzing specifically the oxidation of L-2-hydroxyglutarate to ␣-ketoglutarate. This enzyme is mainly expressed in liver and kidney but also at lower levels in heart, brain, and other tissues. Subcellular fractionation indicates that the liver enzyme is present in mitochondria, where it is bound to membranes. Based on this information, a database search led to the identification of a gene encoding a human hypothetical protein homologous to bacterial FAD-dependent malate dehydrogenases and targeted to mitochondria. The gene encoding this protein, present on chromosome 14q22.1, was found to be in a region homozygous in patients with L-2-hydroxyglutaric aciduria from two consanguineous families. Three mutations that replaced a highly conserved residue (Lys-71-Glu and Glu-176-Asp) or removed exon 9 were identified in homozygous state in patients from three distinct families and were found to cosegregate with the disease. It is concluded that L-2-hydroxyglutarate is normally metabolized to ␣-ketoglutarate in mammalian tissues and that L-2-hydroxyglutaric aciduria is caused by mutations in the gene that most likely encodes L-2-hydroxyglutarate dehydrogenase. The pathological findings observed in this metabolic disorder must therefore be due to a toxic effect of L-2-hydroxyglutarate on the central nervous system. inborn error of metabolism ͉ leukoencephalopathy ͉ ataxia A s a neurometabolic disorder, L-2-hydroxyglutaric aciduria is characterized by the presence of elevated concentrations of L-2-hydroxyglutaric acid in plasma, cerebrospinal fluid, and urine (1-3). Clinically, the affection is characterized by progressive ataxia, mental deficiency with subcortical leukoencephalopathy, and cerebellar atrophy. As of 1996, Ͼ40 patients were known worldwide (3). The disease appears to be recessively transmitted, but the enzymatic defect leading to this condition is presently unknown, largely because of poor knowledge on the origin and fate of L-2-hydroxyglutarate. A NAD-dependent dehydrogenase acting on this compound has been reported to be present in liver (4). However, this enzyme displays a very high K m for L-2-hydroxyglutarate (Ϸ10 mM), making it unsuitable to consume this substrate at physiologically relevant concentrations (probably of the order of 1 M). Furthermore, it is not deficient in patients with L-2-hydrox yglutaric aciduria (5). L-2-hydroxyglutarate dehydrogenase activity transferring its electrons to pyocyanin was partially characterized Ϸ70 years ago by Weil-Malherbe (6), who found it to be mostly active in heart, kidney, and brain. However, no oxidation of L-2-hydroxyglutarate by rat liver mitochondria was later found by Lindahl and coworkers (7). Furthermore, rat ti...