Inflammatory bowel disease in Hermansky-Pudlak syndrome: a retrospective single-centre cohort study.

BACKGROUND: Knowledge about inflammatory bowel disease (IBD) in patients with Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterized by defective biogenesis of lysosome-related organelles, could provide insights into IBD in general. OBJECTIVE: To expand the understanding of IBD in patients with HPS. METHODS: Retrospective review of records from patients with HPS evaluated at the National Institutes of Health Clinical Center from 1995 to 2019 was conducted. Clinical features of IBD, genotyping results and histologic findings of colectomy specimens were analysed. RESULTS: IBD affected 37 (14.2%; 12 male, 25 female) of 261 patients with HPS. Median age of onset was 17 years; range was 1 to 52 years. The most common symptoms of HPS IBD were hematochezia, abdominal pain and loose stools. Fistulae or extra-intestinal manifestations developed in 30% or 22%, respectively. Genotyping showed that patients with biallelic variants in HPS1, HPS3, HPS4 or HPS6 were diagnosed with IBD. Six children had very early-onset IBD. Patients with HPS-3 had mild manifestations of IBD. Medical therapy and bowel resection were utilized to treat 73% and 35% of patients with HPS IBD, respectively; 7 of 13 patients receiving anti-tumor necrosis factor alpha therapy had prolonged clinical responses. Active cryptitis, chronic inflammatory changes, granulomas and ceroid lipofuscinosis were histopathologic findings in three colectomy specimens. CONCLUSIONS: IBD resembling Crohn's disease affects some patients with HPS; genetic heterogeneity is a feature of HPS IBD. HPS3 is a new gene associated with human IBD. Very early-onset IBD can develop in HPS.

Biallelic mutations in mitochondrial tryptophanyl-tRNA synthetase cause Levodopa-responsive infantile-onset Parkinsonism.

Mitochondrial aminoacyl-tRNA synthetases (mtARSs) are essential, ubiquitously expressed enzymes that covalently attach amino acids to their corresponding tRNA molecules during translation of mitochondrial genes. Deleterious variants in the mtARS genes cause a diverse array of phenotypes, many of which involve the nervous system. Moreover, distinct mutations in mtARSs often cause different clinical manifestations. Recently, the gene encoding mitochondrial tryptophanyl tRNA synthetase (WARS2) was reported to cause 2 different neurological phenotypes, a form of autosomal recessive intellectual disability and a syndrome of severe infantile-onset leukoencephalopathy. Here, we report the case of a 17-year-old boy with compound heterozygous mutations in WARS2 (p.Trp13Gly, p.Ser228Trp) who presented with infantile-onset, Levodopa-responsive Parkinsonism at the age of 2 years. Analysis of patient-derived dermal fibroblasts revealed decreased steady-state WARS2 protein and normal OXPHOS content. Muscle mitochondrial studies suggested mitochondrial proliferation without obvious respiratory chain deficiencies at the age of 9 years. This case expands the phenotypic spectrum of WARS2 deficiency and emphasizes the importance of mitochondrial protein synthesis in the pathogenesis of Parkinsonism.

Mitochondrial epileptic encephalopathy, 3-methylglutaconic aciduria and variable complex V deficiency associated with TIMM50 mutations.

Mitochondrial encephalopathies are a heterogeneous group of disorders that, usually carry grave prognosis. Recently a homozygous mutation, Gly372Ser, in the TIMM50 gene, was reported in an abstract form, in three sibs who suffered from intractable epilepsy and developmental delay accompanied by 3-methylglutaconic aciduria. We now report on four patients from two unrelated families who presented with severe intellectual disability and seizure disorder, accompanied by slightly elevated lactate level, 3-methylglutaconic aciduria and variable deficiency of mitochondrial complex V. Using exome analysis we identified two homozygous missense mutations, Arg217Trp and Thr252Met, in the TIMM50 gene. The TIMM50 protein is a subunit of TIM23 complex, the mitochondrial import machinery. It serves as the major receptor in the intermembrane space, binding to proteins which cross the mitochondrial inner membrane on their way to the matrix. The mutations, which affected evolutionary conserved residues and segregated with the disease in the families, were neither present in large cohorts of control exome analyses nor in our ethnic specific exome cohort. Given the phenotypic similarity, we conclude that missense mutations in TIMM50 are likely manifesting by severe intellectual disability and epilepsy accompanied by 3-methylglutaconic aciduria and variable mitochondrial complex V deficiency. 3-methylglutaconic aciduria is emerging as an important biomarker for mitochondrial dysfunction, in particular for mitochondrial membrane defects.

Perspectives on distal myopathy with rimmed vacuoles or hereditary inclusion body myopathy: contributions from an animal model. Lack of sialic acid, a central determinant in sugar chains, causes myopathy?

Distal myopathy with rimmed vacuoles (DMRV) or hereditary inclusion body myopathy (hIBM) is an adult onset slowly progressive myopathy secondary to mutations in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene that encodes a bifunctional enzyme which catalyzes the rate-limiting step in sialic acid biosynthesis. Many hypotheses have been proposed to explain why patients develop weakness and atrophy, but are most views are obscure and thus are still considered controversial, partly because of the lack of an appropriate model with which these theories could be clarified. In this review, we briefly summarize the progress in DMRV research, and highlight efforts of researchers in generating the animal model for this myopathy.