Case Report: Pathogenic MYH9 c.5797delC Mutation in a Patient With Apparent Thrombocytopenia and Nephropathy

MYH9-related disease or disorder (MYH9-RD) is an autosomal dominant disease caused by mutations in the MYH9 gene. Mutations in this gene initially affect the hemic system, and other manifestations may evolve with age. Here, we report the case of a 46-year-old Chinese woman with MYH9-RD who was primarily misdiagnosed with idiopathic thrombocytopenia purpura. Exome sequencing of the patient, and the mother and son of the patient revealed a deletion mutation c.5797delC (p. R1933Efs*15) in exon 41 (encoding non-helical tailpiece, NHT) of the MYH9 gene, which consequently led to a frameshift mutation. To the best of our knowledge, this mutation has been reported in Italy once, while the substitution mutation c.5797 C>T is the most frequent mutation. Mutations that affect the NHT region cause thrombocytopenia throughout life; however, our patient presented with a more severe phenotype than previously reported, including thrombocytopenia, inclusion bodies in neutrophils, sensorineural hearing loss, nephropathy, and abnormal liver enzymes. Our goal in the current case is to prevent further progression of renal involvement and to identify other affected members in this family to provide early intervention. This case may raise awareness of MYH9-RD when diagnosing thrombocytopenia and improve our understanding of this condition.

JAK2V617F Mutation Promoted IL-6 Production and Glycolysis via Mediating PKM1 Stabilization in Macrophages

A substitution mutation of valine to phenylalanine at codon encoding position 617 of the Janus kinase 2 (JAK2) gene (JAK2V617F) has been detected in myeloid cells of some individuals with higher levels of proinflammatory cytokine production such as interleukin (IL)-6. However, the mechanisms by which JAK2V617F mutation mediating those cytokines remain unclear. We, therefore, established JAK2V617F-expressing murine macrophages (JAK2V617F macrophages) and found that the levels of p-STAT3 were markedly elevated in JAK2V617F macrophages in association with an increase in IL-6 production. However, inhibition of STAT3 by C188-9 significantly decreased the production of IL-6. Furthermore, the JAK2V617F mutation endowed macrophages with an elevated glycolytic phenotype in parallel with aberrant expression of PKM1. Interestingly, silencing of PKM1 inactivated STAT3 in parallel with reduced IL-6 production. In contrast, ectopic expression of PKM1 elevated IL-6 production via STAT3 activation. Importantly, the JAK2V617F mutation contributed to PKM1 protein stabilization via blockade of lysosomal-dependent degradation via chaperone-mediated autophagy (CMA), indicating that the JAK2V617F mutation could protect PKM1 from CMA-mediated degradation, leading to activation of STAT3 and promoting IL-6 production.

Low Base-Substitution Mutation Rate but High Rate of Slippage Mutations in the Sequence Repeat-Rich Genome of Dictyostelium discoideum

We describe the rate and spectrum of spontaneous mutations for the social amoeba Dictyostelium discoideum, a key model organism in molecular, cellular, evolutionary and developmental biology. Whole-genome sequencing of 37 mutation accumulation lines of D. discoideum after an average of 1,500 cell divisions yields a base-substitution mutation rate of 2.47 × 10−11 per site per generation, substantially lower than that of most eukaryotic and prokaryotic organisms, and of the same order of magnitude as in the ciliates Paramecium tetraurelia and Tetrahymena thermophila. Known for its high genomic AT content and abundance of simple sequence repeats, we observe that base-substitution mutations in D. discoideum are highly A/T biased. This bias likely contributes both to the high genomic AT content and to the formation of simple sequence repeats in the AT-rich genome of Dictyostelium discoideum. In contrast to the situation in other surveyed unicellular eukaryotes, indel rates far exceed the base-substitution mutation rate in this organism with a high proportion of 3n indels, particularly in regions without simple sequence repeats. Like ciliates, D. discoideum has a large effective population size, reducing the power of random genetic drift, magnifying the effect of selection on replication fidelity, in principle allowing D. discoideum to evolve an extremely low base-substitution mutation rate.