Abstract In eukaryotes, the elongation phase of transcription by RNA polymerase II (RNAP II) is regulated by the transcription elongation factor b (P-TEFb), composed of Cyclin-T1 and cyclin-dependent kinase 9. The release of RNAP II is mediated by phosphorylation through P-TEFb that in turn is under control by the inhibitory 7SK small nuclear ribonucleoprotein (snRNP) complex. The 7SK snRNP consists of the 7SK non-coding RNA and the proteins MEPCE, LARP7, and HEXIM1/2. Biallelic LARP7 loss-of-function variants underlie Alazami syndrome characterized by growth retardation and intellectual disability. We report a boy with global developmental delay and seizures carrying the de novo MEPCE nonsense variant c.1552 C > T/p.(Arg518*). mRNA and protein analyses identified nonsense-mediated mRNA decay to underlie the decreased amount of MEPCE in patient fibroblasts followed by LARP7 and 7SK snRNA downregulation and HEXIM1 upregulation. Reduced binding of HEXIM1 to Cyclin-T1, hyperphosphorylation of the RNAP II C-terminal domain, and upregulated expression of ID2 , ID3 , MRPL11 and snRNAs U1, U2 and U4 in patient cells are suggestive of enhanced activation of P-TEFb. Flavopiridol treatment and ectopic MEPCE protein expression in patient fibroblasts rescued increased expression of six RNAP II-sensitive genes and suggested a possible repressive effect of MEPCE on P-TEFb-dependent transcription of specific genes.
Abstract Biallelic variants in POLR3A cause 4H leukodystrophy, characterized by hypomyelination in combination with cerebellar and pyramidal signs and variable non-neurological manifestations. Basal ganglia are spared in 4H leukodystrophy, and dystonia is not prominent. Three patients with variants in POLR3A, an atypical presentation with dystonia, and MR involvement of putamen and caudate nucleus (striatum) and red nucleus have previously been reported. Genetic, clinical findings and 18 MRI scans from nine patients with homozygous or compound heterozygous POLR3A variants and predominant striatal changes were retrospectively reviewed in order to characterize the striatal variant of POLR3A -associated disease. Prominent extrapyramidal involvement was the predominant clinical sign in all patients. The three youngest children were severely affected with muscle hypotonia, impaired head control, and choreic movements. Presentation of the six older patients was milder. Two brothers diagnosed with juvenile parkinsonism were homozygous for the c.1771-6C > G variant in POLR3A ; the other seven either carried c.1771-6C > G ( n = 1) or c.1771-7C > G ( n = 7) together with another variant (missense, synonymous, or intronic). Striatal T2-hyperintensity and atrophy together with involvement of the superior cerebellar peduncles were characteristic. Additional MRI findings were involvement of dentate nuclei, hila, or peridentate white matter (3, 6, and 4/9), inferior cerebellar peduncles (6/9), red nuclei (2/9), and abnormal myelination of pyramidal and visual tracts (6/9) but no frank hypomyelination. Clinical and MRI findings in patients with a striatal variant of POLR3A -related disease are distinct from 4H leukodystrophy and associated with one of two intronic variants, c.1771-6C > G or c.1771-7C > G, in combination with another POLR3A variant.
Abstract FZR1 , which encodes the Cdh1 subunit of the Anaphase Promoting Complex, plays an important role in neurodevelopment by regulating cell cycle and by its multiple post-mitotic functions in neurons. In this study, evaluation of 250 unrelated patients with developmental epileptic encephalopathies (DEE) and a connection on GeneMatcher led to the identification of three de novo missense variants in FZR1 . Two variants led to the same amino acid change. All individuals had a DEE with childhood onset generalized epilepsy, intellectual disability, mild ataxia and normal head circumference. Two individuals were diagnosed with the DEE subtype Myoclonic Atonic Epilepsy (MAE). We provide gene burden testing using two independent statistical tests to support FZR1 association with DEE. Further, we provide functional evidence that the missense variants are loss-of - function (LOF) alleles using Drosophila neurodevelopment assays. Using three fly mutant alleles of the Drosophila homolog fzr and overexpression studies, we show that patient variants do not support proper neurodevelopment. With the recent report of a patient with neonatal-onset DEE with microcephaly who also carries a de novo FZR1 missense variant, our study consolidates the relationship between FZR1 and DEE, and expands the associated phenotype. We conclude that heterozygous LOF of FZR1 leads to DEE associated with a spectrum of neonatal to childhood onset seizure types, developmental delay and mild ataxia. Microcephaly can be present but is not an essential feature of FZR1 -encephalopathy. In summary, our approach of targeted sequencing using novel gene candidates and functional testing in Drosophila will help solve undiagnosed MAE/DEE cases.
Heterozygous loss-of-function mutations in the X-linked CASK gene cause progressive microcephaly with pontine and cerebellar hypoplasia (MICPCH) and severe intellectual disability (ID) in females. Different CASK mutations have also been reported in males. The associated phenotypes range from nonsyndromic ID to Ohtahara syndrome with cerebellar hypoplasia. However, the phenotypic spectrum in males has not been systematically evaluated to date.We identified a CASK alteration in 8 novel unrelated male patients by targeted Sanger sequencing, copy number analysis (MLPA and/or FISH) and array CGH. CASK transcripts were investigated by RT-PCR followed by sequencing. Immunoblotting was used to detect CASK protein in patient-derived cells. The clinical phenotype and natural history of the 8 patients and 28 CASK-mutation positive males reported previously were reviewed and correlated with available molecular data.CASK alterations include one nonsense mutation, one 5-bp deletion, one mutation of the start codon, and five partial gene deletions and duplications; seven were de novo, including three somatic mosaicisms, and one was familial. In three subjects, specific mRNA junction fragments indicated in tandem duplication of CASK exons disrupting the integrity of the gene. The 5-bp deletion resulted in multiple aberrant CASK mRNAs. In fibroblasts from patients with a CASK loss-of-function mutation, no CASK protein could be detected. Individuals who are mosaic for a severe CASK mutation or carry a hypomorphic mutation still showed detectable amount of protein.Based on eight novel patients and all CASK-mutation positive males reported previously three phenotypic groups can be distinguished that represent a clinical continuum: (i) MICPCH with severe epileptic encephalopathy caused by hemizygous loss-of-function mutations, (ii) MICPCH associated with inactivating alterations in the mosaic state or a partly penetrant mutation, and (iii) syndromic/nonsyndromic mild to severe ID with or without nystagmus caused by CASK missense and splice mutations that leave the CASK protein intact but likely alter its function or reduce the amount of normal protein. Our findings facilitate focused testing of the CASK gene and interpreting sequence variants identified by next-generation sequencing in cases with a phenotype resembling either of the three groups.
Recently, mutations in the PLPBP gene were described as a novel cause for vitamin B6-responsive epilepsy. We report the outcome in case of a male adolescent with a novel homozygous missense variant in PLPBP who was never treated with pyridoxine until the age of 16 years. He presented with only mild cognitive impairment and an early-onset, well-controlled epilepsy. In our patient, excessive seizure clusters and anxiety states occurred intermittently, suggesting that the combination might be a hallmark in untreated patients. Thus, mutations in PLPBP should be addressed even in adolescent patients with only mild learning disabilities and relatively good seizure control over the years.
Abstract Metabolic diseases such as obesity, type 2 diabetes mellitus and non-alcoholic steatohepatitis (NASH) are closely linked to aberrant synthesis of endogenous fatty acids in the liver, called de novo lipogenesis, which is mediated by the enzyme fatty acid synthase (FASN). Endogenously synthesized fatty acids are either saturated or monounsaturated and can adversely affect metabolic health through mechanisms that are not sufficiently understood. Here we show that lipogenesis critically determines the use of food-derived, metabolically beneficial polyunsaturated fatty acids (PUFA). We found a patient with a hypofunctional heterozygous de novo Arg2177Cys mutation in FASN, which resulted in a cysteine-dependent, non-enzymatic acetylation of FASN and decreased protein stability. Remarkably, the patient showed markedly elevated levels of polyunsaturated fatty acids, whereas patients with high FASN expression in the liver showed diminished levels. Moreover, pharmacological intervention with the FASN-inhibitor TVB-2640 in patients with NASH was sufficient to increase the rate of PUFA use in circulating lipids. In line, the incorporation rate of supplemented omega-3 PUFA in obesogenic diet could be dramatically increased by reducing the lipogenesis rate in mice. Mechanistically, we show that fatty acid storage preferences are determined by an active, enzymatic process dependent on FASN and DGAT2. Our results demonstrate that low lipogenesis rates increase the efficiency of PUFA incorporation into complex lipids, whereas high lipogenesis rates lead to low PUFA use. This has critical clinical implications for the prediction of low therapeutic success of omega-3 supplementation in patients with high lipogenesis and provides evidence for the urgent development of combined therapy options targeting lipogenesis and PUFA supplementation.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
