The Study Of Gene Mutation In Patients With Mitochondrial Encephalomyopathies

Mitochondria are important organelles in eukaryotic cells, they providethe energy of the place through oxidative metabolism. They provide about90%of the energy of the body. Mitochondrial DNA (mtDNA) genome in thenucleus chromosome, with self-replication, transcription and coding functions,genetic control system is a set of relatively independent, but subject to thecontrol of nuclear DNA. The mtDNA molecule of the human super-helicalstructure of double-stranded closed-loop, long16569bp. It has37codinggenes, these genes were closely spaced, any randomness of mutations cancause mitochondrial dysfunction. MtDNA was exposed, neither histoneprotection, the lack of a more effective repair system, vulnerable to the processof oxidative phosphorylation to produce oxygen free radicaldamage. Biological environment and genetics status, makes mtDNAvulnerable to injury mutation. The mode of inheritance of mtDNA ismaternally inherited and can not be re-combination of mutations alongmaternal continuous accumulation.Mitochondrial encephalopathies, are a group of mitochondrial structuraland functional abnormalities caused by mutation of the ATP synthesis. Thisdisease are caused by the lack of a rare multi-system disease, lesions of thecentral nervous system and muscle tissue as the main performance involvingthe other system, according to its different clinical manifestations can bedivided into a variety of clinical syndromes.The occurrence of mitochondrial encephalomyopathies withmitochondrial DNA mutations. From Anderson to complete the full length ofhuman mtDNA sequencing, Wallace confirmed the point mutation in Leber’shereditary optic nerve degeneration, Holt confirm the mtDNA deletion inmitochondrial encephalomyopathy, the mitochondrial disease has entered a rapid development of stage. About more than100different pathological pointmutation and more than200types of absence have been found.With the gradual increase mitochondrial encephalomyopathy, thedetection rate of the disease in recent years has increased. Its diagnosisdepends mainly on the muscle biopsy, pathological MGT staining find theragged-red fiber (RRF) and the class of crystalline-like inclusion bodies is oneof the main basis for the diagnosis of the disease. DNA mutation analysis isthe diagnosis of mitochondrial disease is the most sensitive method for thediagnosis gene level evidence to increase the reliability of diagnosis.The structure and function of mitochondrial are very special, somitochondrial encephalomyopathies have wide variety of clinicalpresentations with genetically heterogeneous,which make the clinicaldiagnosis of mitochondrial dieases is frequently difficult. Therefore, we makea study of gene mutation in patients with mitochondrial encephalomyopathies,which can provide diagnosis method of the disease. To investigate the geneticcharacteristics of mitochondrial encephalopathy, detect the gene mutations inblood of the family members, which can provide relevant genetic counselingfor the family.Objective:(1) To investigate the histopathologic findings of patientswith mitochondrial encephalopathy and point mutation of mtDNA genes,which can provide diagnosis method of the disease;(2) To investigate thegenetic characteristics of mitochondrial encephalopathy, detect the genemutations in blood of the family members, which can provide relevantgenetic counseling for the family.Methods: This study divided into two groups, there were17cases in theobservation group, who with pathologically diagnosed as mitochondrialencephalopathy; there were20cases in the control group, who with normalmuscle pathology or find no RRF in the muscle. Serially sectioned frozenmuscle specimens with a battery of histochemical stains were reviewed underlight microscope. Total DNA was extracted from muscle specimens or(and)whole blood. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis with restriction enzyme was performedto confirm these common point mutations, which include mtDNA A3243G,A8344G, T8993G, T8993C, T3271C and T9176C. In one family which withfamily history, the A3243G mutation was observed in blood sample amongsome family members.Results:(1) In the experimental group,17patients with typicalpathological findings: GMT staining shows ragged red fibers (RRF), gatheredas part of the sarcolemma or muscle fibers red sediment, and depth within thesarcoplasmic;(2) In the experimental group, the mtDNA A3243G mutationwas identified in one patient with MELAS and four patients withmitochondrial myopathy; the same point mutation was also be identified inone case in the control group which muscle pathology result was normal. ThemtDNA A8344G, T8993G, T8993C, T3271C, and T9176C point mutationswere not observed in all of the cases. The mutation proportion of mtDNAA3243G from case1to case5were65.32%,63.28%,37.00%,48.81%and59.81%. And the proportion of mtDNA A3243G of the case in the controlgroup, whose muscle pathology result was normal was32.51%.(3) Case3tocase5, the A3243G mutation rate of these three cases in muscle and bloodwere38.01%and22.76%,49.27%and21.96%,61.80%and50.51%, therewas high proportion of mutation in the muscle than in the blood.(4) Thefamily showed that patient5(IV-13) and his two brothers (IV-7, IV-9), onesister(IV-5) and two sons of his sister(V-5, V-6) are the existence A3243Gmutation, while the A3243G mutation was not be found in the two sons of theproband and his brother’s children, who were the offspring of male carriers inthe family. The A3243G mutation ratio in blood of IV-13, IV-5, IV-7were:53.62%,61.10%,26.75%and36.48%. The A3243G mutation ratio in blood ofV-5and V-6were60.05%and62.80%.Conclusion: The clinical manifestations of mitochondrial myopathy iscomplex and diverse, the same mutation can lead to different clinicalmanifestations. The mtDNA A3243G mutation is the most commondisease-causing mutation of mitochondrial encephalomyopathies. Genetic testing for the diagnosis of the disease gene level evidence to increase thereliability of diagnosis. Screening, the patient’s family can be found inasymptomatic carriers, to facilitate the provision of appropriate geneticcounseling.