Analysis Of HMBS Variants In Chinese Patients With Acute Intermittent Porphyria And Pathogenic Study On C.1078＿~*46del

Objective:Acute intermittent porphyria(AIP)is an autosomal dominant disease caused by the loss of function of HMBS.The reported HMBS variants have been increasing gradually in China,but there is a lack of epidemiological data and more systematic analysis.This paper aims to initially reveal the characteristics of HMBS variants in China through the reported variants.Pathogenicity of the c.1078_* 46 del was studied to provide further supporting evidence for clinical diagnosis and new ideas for the interpretation of 3 ′variants.Methods:Pubmed,CNKI,Wanfang Medicine,and CQVIP database were searched until September 2021 to obtain relevant literature.HMBS variants reported in the literature were collected and the characteristics of type and distribution were analyzed.The preliminary prediction of their pathogenicity was made by using Mutation Taster,Polyphen-2,SIFT and PROVEAN.The consistency of four software was evaluated by intraclass correlation coefficient(ICC).The pathogenic study of c.1078_* 46 del previously reported:1)Expression validation of in vivo :RNA were collected from blood samples for validation of abnormal m RNA transcripts and qualitative and quantitative analysis of m RNA expression using reverse transcription PCR technology and agarose gel electrophoresis.2)Expression validation in vitro:Wild-type and mutant vectors were constructed and transfected into the cultured cells.The expression between mutant andwild type at m RNA and protein levels were compared using c DNA q PCR and Western blot,respectively.Results:Results of characteristics analysis of HMBS variants:A total of 30 articles reporting the HMBS variants were included in China,most of which were case reports.90 different variants were identified in the 128 AIP patients,including 33 missense variants(36.8%),19 small deletions(21.1%),21 splicing variants(23.3%),10 nonsense variants(11.1%),3 insertions(3.3%),2 repeats(2.2%),1synonymous variant(1.1%),and 1 large deletion(1.1%).Exon variants were mainly concentrated in exon 11 and exon 14.The most common variant was p.R173 W reported in 15 families,followed by p.R225 X reported in 10 families.It was mainly concentrated in Taiwan,Beijing and Hebei,and sporadic cases were in other provinces and cities.Reports from Hong Kong and Taiwan were from large local hospitals,and almost all reports in the mainland were from third-class hospitals.Results of pathogenic prediction :The prediction of Mutation Taster showed that p.H305N、c.1071 del T、c.772-17A>G、c.962G>A and c.1078_*46del were polymorphism,but the others were disease causing.The predictions of various software for missense variants suggested that the results of c.988G>C,p.H305 N,p.D359 N were not consistent.Multiple software had good consistency in the prediction of the all missense variants(ICC=0.564,95%CI=0.396~0.722).However,the consistency of predicting missense variants in the exon 14 was poor(ICC=0.364,95%CI=-0.053~0.874).Results of the pathogenic study on c.1078_* 46del:The experiments in vivo demonstrated that there was abnormal transcript in the patient with decreased expression at the m RNA level compared with healthy control.The experiments in vitro showed that it significantly reduced the expression level of the gene either at the m RNA or protein level.Conclusion:1.Analysis of HMBS variants in China showed that missense variants accounted for the largest proportion,followed by splicing variants.Exon variants mainly concentrated in exon 11 and 14;2.The most common variant in China was p.R173 W,which was a known high-frequency variants abroad;3.Bioinformatic software had limitations in predicting pathogenicity of variants;4.C.1078_* 46 del was able to significantly reduce the expression level of HMBS,which was the one of main cause of AIP in this patient.