Identification of three in-frame deletion mutations in MYH9 disorders suggesting an important hot spot for small rearrangements in MYH9 exon 24

Two Cases of the MYH9 Disorder Fechtner Syndrome Diagnosed from Observation of Peripheral Blood Cells before End-Stage Renal Failure

As a MYH9 disorder, Fechtner syndrome is characterized by nephritis, giant platelets, granulocyte inclusion bodies (Döhle-like bodies), cataract, and sensorineural deafness. Observation of peripheral blood smear for the presence of thrombocytopenia, giant platelets, and granulocyte inclusion bodies (Döhle-like bodies) is highly important for the early diagnosis of MYH9 disorders. In our two cases, sequencing analysis of the MYH9 gene indicated mutations in exon 24. Both cases were diagnosed as the MYH9 disorders Fechtner syndrome before end-stage renal failure on the basis of the observation of peripheral blood smear.

Novel mutations associated with autosomal-dominant congenital cataract identified in Chinese families

As the leading cause of impaired vision, congenital cataracts, particularly autosomal dominant congenital cataract (ADCC), have been considered as a hereditary disease. The present study aimed to identify genetic defects in Chinese pedigrees with ADCC. A total of 6 Chinese families with ADCC were included, comprising 103 members and 27 patients assessed in total. Genomic DNA samples were extracted from the peripheral blood of probands; mutations were determined using a specific eye disease enrichment panel with next-generation sequencing. Following pathogenicity prediction, sites with notable pathogenicity were screened for further validation. Sanger sequencing was performed in the remaining individuals of the families and 100 normal controls. The pathogenic effects of the mutations, including amino acid substitutions, as well as structural and functional alterations of proteins linked to ADCC, were investigated via bioinformatics analysis. A total of seven mutations in six candidate genes associated with ADCC were identified in the 6 families: Myosin heavy chain 9 (MYH9) c.4150G>C, β-crystallin A4 (CRYBA4) c.169T>C, RPGR-interacting protein 1 (RPGRRIP1) c.2669G>A, wolframin (WFS1) c.1235T>C, CRYBA4 c.26C>T, Ephrin receptor subfamily 2 (EPHA2) c.2663+1G>A and paired box 6 (PAX6) c.11-2A>G. The seven mutations were only detected in affected individuals. Among them, there were three novel mutations (MYH9: c.4150G>C; CRYBA4: c.169T>C; RPGRRIP1: c.2669G>A) and four previously reported ones. Mutations in RPGRIP1 (c.2669G>A) and CRYBA4 (c.26C>T) were predicted to be benign according to bioinformatics analysis. Conversely, other mutations in EPHA2, PAX6, MYH9, CRYBA4 (c.169T>C) and WFS1 were determined to be pathogenic. The present study reported two novel heterozygous mutations (MYH9 c.4150G>C and CRYBA4 c.169T>C) identified by analyzing 6 Chinese families with ADCC, supporting their important roles in the development of the disease.

Use of Targeted High-Throughput Sequencing for Genetic Classification of Patients with Bleeding Diathesis and Suspected Platelet Disorder

Inherited platelet disorders (IPD) form a rare and heterogeneous disease entity that is present in about 8% of patients with non-acquired bleeding diathesis. Identification of the defective cellular pathway is an important criterion for stratifying the patient's individual risk profile and for choosing personalized therapeutic options. While costs of high-throughput sequencing technologies have rapidly declined over the last decade, molecular genetic diagnosis of bleeding and platelet disorders is getting more and more suitable within the diagnostic algorithms. In this study, we developed, verified, and evaluated a targeted, panel-based next-generation sequencing approach comprising 59 genes associated with IPD for a cohort of 38 patients with a history of recurrent bleeding episodes and functionally suspected, but so far genetically undefined IPD. DNA samples from five patients with genetically defined IPD with disease-causing variants in WAS , RBM8A , FERMT3 , P2YR12 , and MYH9 served as controls during the validation process. In 40% of 35 patients analyzed, we were able to finally detect 15 variants, eight of which were novel, in 11 genes, ACTN1 , AP3B1 , GFI1B , HPS1 , HPS4 , HPS6 , MPL , MYH9 , TBXA2R , TPM4 , and TUBB1 , and classified them according to current guidelines. Apart from seven variants of uncertain significance in 11% of patients, nine variants were classified as likely pathogenic or pathogenic providing a molecular diagnosis for 26% of patients. This report also emphasizes on potentials and pitfalls of this tool and prospectively proposes its rational implementation within the diagnostic algorithms of IPD.

MYH9: Structure, functions and role of non-muscle myosin IIA in human disease

The MYH9 gene encodes the heavy chain of non-muscle myosin IIA, a widely expressed cytoplasmic myosin that participates in a variety of processes requiring the generation of intracellular chemomechanical force and translocation of the actin cytoskeleton. Non-muscle myosin IIA functions are regulated by phosphorylation of its 20 kDa light chain, of the heavy chain, and by interactions with other proteins. Variants of MYH9 cause an autosomal-dominant disorder, termed MYH9-related disease, and may be involved in other conditions, such as chronic kidney disease, non-syndromic deafness, and cancer. This review discusses the structure of the MYH9 gene and its protein, as well as the regulation and physiologic functions of non-muscle myosin IIA with particular reference to embryonic development. Moreover, the review focuses on current knowledge about the role of MYH9 variants in human disease.

Macrothrombocytopenia With Congenital Bilateral Cataracts: A Phenotype of MYH9 Disorder With Exon 24 Indel Mutations

MYH9 disorder is characterized by large platelets and granulocyte inclusion bodies, and can be complicated with young-adult onsets of nephropathy, sensorineural hearing loss, and cataracts. Congenital cataracts in patients with MYH9 disorder is rare, and their etiology has not been elucidated. We report a 3-year-old patient with MYH9 disorder who had a p.E1066_A1072del mutation and developed cataracts congenitally. A review of the literature reveals that patients with an MYH9 exon 24 indel mutation, including p.E1066_A1072del, are susceptible to developing congenital cataracts and should be followed closely for other nonhematological complications.

MYH9-related disease: description of a large Chinese pedigree and a survey of reported mutations

We describe a large four-generational Chinese pedigree segregating MYH9 -related disease caused by a V1516L mutation. The clinical findings supported previously established genotype-phenotype correlations, and also demonstrated interindividual variability of disease manifestations even within the same family. The same mutation was previously reported in another Chinese pedigree but resulting from a different DNA substitution. Analyzing the patterns of previously reported mutations revealed a limited spectrum of pathogenic variants. The implications of this finding are discussed.

MYH9-related disease: five novel mutations expanding the spectrum of causative mutations and confirming genotype/phenotype correlations

MYH9-related disease (MYH9-RD) is a rare autosomal dominant syndromic disorder caused by mutations in MYH9, the gene encoding for the heavy chain of non-muscle myosin IIA (myosin-9). MYH9-RD is characterized by congenital macrothrombocytopenia and typical inclusion bodies in neutrophils associated with a variable risk of developing sensorineural deafness, presenile cataract, and/or progressive nephropathy. The spectrum of mutations responsible for MYH9-RD is limited. We report five families, each with a novel MYH9 mutation. Two mutations, p.Val34Gly and p.Arg702Ser, affect the motor domain of myosin-9, whereas the other three, p.Met847_Glu853dup, p.Lys1048_Glu1054del, and p.Asp1447Tyr, hit the coiled-coil tail domain of the protein. The motor domain mutations were associated with more severe clinical phenotypes than those in the tail domain.

A Trp33Arg mutation at exon 1 of the MYH9 gene in a Korean patient with May-Hegglin anomaly

In this report, we describe a Korean patient with May-Hegglin anomaly from a mutation of the MYH9 gene. The proband was a 21-year-old man with thrombocytopenia. He did not have a bleeding tendency. His neutrophil count was normal at 7490/mm³; however, the neutrophils contained abnormal basophilic inclusions in their cytoplasm. The platelet count was decreased at 15,000/mm³ with giant platelets. Coagulation test results were not remarkable. Direct sequencing of MYH9 revealed that he was heterozygous for a mutation in exon 1, which was a 97T>A substitution mutation affecting codon 33, substituting tryptophan with arginine (Trp33Arg). Family study showed that both of his parents had normal phenotype and genotypes, indicating a de novo occurrence of the mutation in the proband.

Non-muscle myosin II takes centre stage in cell adhesion and migration

Non-muscle myosin II (NM II) is an actin-binding protein that has actin cross-linking and contractile properties and is regulated by the phosphorylation of its light and heavy chains. The three mammalian NM II isoforms have both overlapping and unique properties. Owing to its position downstream of convergent signalling pathways, NM II is central in the control of cell adhesion, cell migration and tissue architecture. Recent insight into the role of NM II in these processes has been gained from loss-of-function and mutant approaches, methods that quantitatively measure actin and adhesion dynamics and the discovery of NM II mutations that cause monogenic diseases.