Genetic Analysis In A Family Of MYH9-related Disorders

BACKGROUND: MYH9-related disorder(MYH9-RD)is a genetic disease caused by one or more clinical symptoms of MYH9 mutation,with deafness,nephritis,cataract or coagulopathy.Because MYH9-RD is a rare disease,and the blood feature is similar to the idiopathic thrombocytopenic purpura(ITP),hospital often misdiagnose MYH9-RD as ITP,supply unnecessary hormone therapy even the splenectomy.So it is necessary for the suspected MYH9-RD patients to take a genetic diagnosis.OBJECTIVE: In this study,we used DNA sequencing to diagnose a family of patients who were previously misdiagnosed as ITP,in order to find pathogenic mutations and to analyze the relationship between genotype and phenotype.METHODS: Peripheral blood was collected from patients and healthy controls.The morphological characteristics of neutrophils,platelets and its organelles were observed by optical microscope and transmission electron microscope.The PCR primers were designed to amplify the coding sequence of MYH9 according to the NCBI reference sequence.The MYH9 and the mutated region were cloned and sequenced to determine the mutation site and type.The mitochondrial genome sequencing was performed to find the disease-related SNPs.Finally,the influences of variations,as well as the sequence conservativewere predicted by some calculation software.RESULTS: Three major characteristics of MYH9-RD were found in the blood test of 8 patients with "huge platelets,a decrease in platelet count and neutrophils containing inclusion bodies ",the platelets count in one of them was within the lower limit of normal range(122 × 109 / L).Patients had skin easy bruising,sustained purpura symptoms,but the clinical manifestations are slightly different.Gene sequencing results showed that all 8 patients with MYH9 c.5803del G heterozygous deletion,resulting in frameshift mutation,and the non-helix tail at carboxyl terminal of non-muscle myosin heavy chain IIA(NMMHC-IIA)was truncated with a total of 26 amino acid variants(p.Ala1935 Profs * 13).While the family and non-family healthy people didn't have such mutation.These can be observed through transmission electron microscopy: the platelets were heterogeneous in their organelles content,and the numbers of open-canalicular system were proportional to the increased platelet volume.PROVEAN software predicts that the variant have a deleterious effect(score =-3.67 <-2.5),and the Mutation Taster calculation indicates that the amino acid sequence of the mutated region is partially conserved in the mammal,predicting that the mutation can cause disease.CONCLUSION: There were 8 MYH9-RD patients in the pedigrees,and the c.5803 del G was associated with phenotypes,which was the pathogenic mutation of the family.Abnormal phosphorylation of NMMHC –IIA may be a significant cause of the activation of platelets in MYH9-RD patients.The clinical manifestations of patients support international studies on the genotype and phenotype of MYH9-RD,that mutation in the carboxyl terminal tail of NMMHC-IIA protein are mild.Patients are expected not to develop severe kidney disease,cataract or deafness,but do not rule out the possibility of onsetin old age.The c.5803 del G(p.Ala1935 Profs * 13)is a novel mutation reported for the first time.