Research On Clinical Features And Mitochondrial DNA Mutation Analysis Of Hereditary Spastic Paraplegia Type 4 (SPG4) Patients

Background:Hereditary spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group neurodegenerative disorders. SPAST-associated HSP is the most common type of pure autosomal dominant HSP, accounting for 40% to 45% of such cases.Within families and between families, the age of onset, the accompanying symptoms, the disease progression and the severity index of SPG4 patients are all significantly different. In addition, SPG4 clinical phenotype is still incomplete penetrance, gender differences, genetic anticipation phenomena, which brings difficulties in clinical diagnosis, some patients with mild symptoms within the family are often missed. But there is still no big sample study on the clinical characteristics of Chinese patients with SPG4.Mitochondrial dysfunction, directly or indirectly involved in many neurodegenerative diseases such as hereditary spastic paraplegia (HSP), spinocerebellar ataxia (SCA), Huntington disease (HD), and Alzheimer's disease (AD) pathogenesis.It has been reported that a higher mitochondrial DNA (mtDNA) mutation rate was found in SCA, HD and AD patients, in addition, these mutations were also correlated with the clinical characteristics of certain degree.So far, there is no report about mtDNA mutation analysis in patients with SPG4.Objective:To identify the clinical features of Chinese Han patients with SPG4.To discuss the mtDNA mutations of SPG4 genotype and its correlation with the phenotype, this might provide clues to reveal the role of mtDNA in HSP pathogenesis.Methods:Detail follow-up and clinical investigation one by one was carried out to obtain clinical data of 15 Chinese Han population SPG4 family members, in which the probands have been diagnosed as SPG4 in our previous study. Sequencing and MLPA technologies were carried out to detect mutation of SPAST gene in all family members.PCR and direct sequencing technologies were carried out to screen for micro-mutations of MT-LT1,MT-ND1,MT-CO2,MT-TK, MT-ATP8,and MT-ATP6 genes and rearrangement mutations of mtDNA in all SPG4 family members and 70 healthy controls.Results:Fifty-one family members from the 15 Chinese Han population SPG4 pedigrees were diagnosed as HSP patients in clinic after follow-up study. Their mean age at onset was 21.65±14.67, and the mean duration was 22.90±12.93 years. Most patients manifested as "pure" forms, and the stiffness in the legs was often the earliest symptom at the beginning of the disease.Compared with other populations,these SPG4 patients often accompanied with arch foot (52.9%) and bowel disorders(17.6%), while mental retardation (2.0%) was rare.Male patients with lower limb dystonia was more frequent than female (P<0.05),and there was obviously difference between male and female phenotype in certain families. The phenomenon of genetic anticipation was also existed in some maternally inherited families. SPAST gene mutations were found in 64 family members from the 15 SPG4 pedigrees by genetic testing.In addition to 51 cases diagnosed by clinical investigation, there were 13 family members without any symptoms and were considered as "incomplete penetrance".The nonpenetrance rate of these SPG4 patients was from 40% in the group of younger age(1-19years) to 21.1% in the age of 20 to 40, and 14.3% after 40.Twelve novel sequence variations were found by micro-mutation detection of mtDNA genes, in which variations C8513T and T8825C were found in both SPG4 patients and normal family members.All of the sequence variations were in full accordance with maternal inheritance in generational transmission, and no novel mtDNA sequence variation was found in filial generation.At least one type of mtDNA rearrangement was found in 68.8% of SPG4 patients,73.3% of normal family members, and 58.6% of normal controls. There was no significant difference of either one type or multiple type rearrangement rates existed among the three groups (P>0.05).In addition, there is also no significant difference of various rearrangement mutation rates existed between SPG4 patients and incomplete penetrance (P>0.05). But patients with no mtDNA rearrangement mutation had a significantly earlier age at onset (P<0.05).Conclusions:Firstly, most of the Chinese Han patients with SPG4 in this group manifest as "pure" forms, with a young onset and stiffness of both lower extremities as the first symptom, and arched feet and bowel disorder symptoms is common while mental retardation is rare compared with other populations.Secondly, Chinese Han patients with SPG4 in this group have significant genetic and clinical heterogeneity, and obviously incomplete penetrance, gender differences, and genetic anticipation. Thirdly, the rate of mtDNA micro-mutation is low in these Chinese SPG4 patients, furthermore, there is no relationship between the SPG4 gene mutation and disease phenotype.Fourthly, mtDNA rearrangement of these Chinese SPG4 patients has no relationship with either SPG4 gene mutation or incomplete penetrance, while patients with no mtDNA rearrangement have a significantly earlier age at onset.