Mutation Analysis Of PMM2 Gene In Congenital Disorders Of Glycosylation And Literature Review

Research backgroundCongenital disorders of glycosylation(CDG),also known as carbohydrate deficiency glycoprotein syndrome in the past,is a group of single gene diseases that have developed rapidly in the past two decades.In 1980,jaeken,a Belgian professor of Pediatrics,described the first patient with congenital glycosylation disorder.The pathophysiological basis of the disease is abnormal glycosylation process of protein or lipid,that is,oligosaccharide and protein or lipid form glycoprotein or glycolipid process defect under the action of enzyme.Because of the extensive glycosylation process,clinical manifestations involve many systems,the most important of which is the nervous system.At present,more than 100 kinds of CDG have been found,and each type has corresponding glycosylase defects.Most of the congenital glycosylation disorders are rare,with no more than 100 cases worldwide.The most common CDG type is caused by the mutation of phosphomannose mutase 2(PMM2)gene.Nearly 1000 cases have been reported worldwide.PMM2 gene mutation leads to the deficiency of phosphomannose mutase 2,which leads to the failure of mannose-6-phosphate to be converted into mannose-1-phosphate.The clinical manifestations were axial hypotonia,mental retardation,ataxia,esotropia,inverted nipple,abnormal fat pad above buttock,epilepsy,etc.The prognosis of this disease is acceptable.Therefore,the clinical manifestations and laboratory characteristics of the disease are summarized and summarized.In order to reduce the burden on family and society,early diagnosis and early treatment are needed to reduce the incidence rate of inherited diseases.The second generation gene sequencing is completed for patients and their family members,and the genetic pattern and gene mutation site are understood.It can be used as a reference for genetic counseling and prenatal diagnosis.ObjectiveBy collecting and summarizing the clinical data of two children with PMM2-CDG in two unrelated families,the gene mutation type,genetic pattern and abnormal gene source of PMM2-CDG patients were studied by whole exon gene sequencing,and the reported cases in China were reviewed.So as to provide basis for genetic counseling and prenatal diagnosis of patiens and to understand the characteristics of PMM2-CDG disease in China.Method1.Clinical data and biochemical examination characteristics of two subjects and their family members were collected.2.Sample collection:after the approval of the ethics committee of our hospital and the informed consent of the children and their family members,3ml peripheral venous blood samples of the subjects,their first-degree relatives were collected.3.Extraction of genomic DNA:use genedna extraction kit to extract DNA from peripheral venous blood samples4.Establish gene library:use specific kit to establish DNA sample library of research object.5.Computer sequencing:compare the sample concentration and sequencing concentration in the DNA library of the research object,and use Illumina sequencer to carry out computer sequencing.6.First generation sequencing verification:Sanger sequencing method was used to verify the mutation sites and the first-class family corresponding sites of the research object that need to be verified.7.Search "congenital glycosylation disorder,PMM2" and other key words on CNKI,Wanfang medical network,VIP database and PubMed database,collect 7 PMM2-CDG cases in China from 2000 to 2020,and analyze their clinical and genetic characteristics.Result1.A compound heterozygous mutation was found in the PMM2 gene of proband in family 1:missense mutation in exon 1 c.59C>G,missense mutation in exon 8 c.691G>A.Sanger sequencing showed that there were two heterozygous mutations in the exon of PMM2 gene in the proband with congenital glycosylation disorder:the first exon c.59C>G,and the eighth exon c.691G>A.The parents of the proband were heterozygous carriers.2.In pedigree 2,it was found that the PMM2 gene of proband had complex heterozygous mutation:missense mutation of exon 7 c.616T>C,and missense mutation of exon 8 c.710C>T.Sanger sequencing showed that there were two heterozygous mutations in the exon of PMM2 gene in the proband with congenital glycosylation disorder:exon 7 c.616T>C,exon 8 c710C>T.The parents of the proband were heterozygous carriers3.In this case summary,7 cases of PMM2-CDG in China have been reported between 2000 and 2020.In addition,3 cases of PMM2-CDG in this study have 10 cases in total.The age of diagnosis of 10 cases in China is from April to 14 years old,with an average of(3.78±5.28)years old.Male:female:1:4.Among the 10 cases of PMM2-CDG in China,there were 8 cases of motor retardation,7 cases of large liver with increased transaminase,8 cases of small cerebellar volume(atrophy),5 cases of inverted nipple and 6 cases of hypotonia.There was 1 case with ASD,4 cases with gluteal fat pad,6 cases with intraocular strabismus and 3 cases with diarrhea.In 10 cases of PMM2-CDG in China,12 mutations of PMM2 gene were found,including 11 different missense mutations and 1 frameshift mutation.Conclusion1.The proband in the two families was consistent with the clinical manifestations,biochemical examination characteristics and gene mutation types of congenital glycosylation disorder,and the diagnosis was clear.2.The missense mutation of PMM2 gene c.59C>G in family 1 and the human gene database of PMM2 gene c.616T>C in family 2 have not been reported,which is a new mutation and enriches the database of congenital glycosylation abnormal gene mutation at home and abroad.