Risk Factors And Genetic Study Of Polydactyly And Syndactyly

ObjectPolydactyly and syndactyly are the most common congenital hand and foot malformations in neonates,with a incidence of about 0.3/1000～3.6/1000.Besides,the incidence of polydactyly in males is about twice that in females.This malformation can occur as a single disease(non-syndrome type)or combined with other diseases(syndrome type).At present,most of the patients with polydactyly and syndactyly admitted to the clinic are non-syndromic.In this study,two families with a family history of polydactyly and syndactyly were selected to investigate the clinical characteristics of this two families and analyze the pathogenic gene mutations.At the same time,clinical data of 100 patients with polydactyly or syndactyly without family history were collected to explore the role of chemical drugs,virus infection and other environmental factors in the development of fetal acromion.This study wanted to improve the understanding of polydactyly and syndactyly,which is conducive to the genetic counseling and prenatal diagnosis of acromion malformation.MethodsIn this study,the clinical data and imaging data of 102 patients with acral malformation who were admitted to the department of orthopedics of Tianjin children’s hospital in 2018 were included.There were 7 patients and 5 normal family members in 2 polydactyly families,100 patients without family history,and 200 normal controls in this study.All patients were examined by two or more experienced orthopedic surgeons for detailed medical history and physical examination.The examination results were recorded and family charts were drawn.The clinical data including image and biochemical examination were also collected.The genomic DNA was extracted from peripheral blood of patients by DNA Blood Mini Kitfor Whole Exome Sequencing(WES).The suspected pathogenic mutations were verified by Sanger sequencing.At the same time,200 normal controls and normal family members in this family were also tested.Poly Phen2 and PROVEAN were used to predict the function of the mutation found in family 1 that were suspected to be pathogenic.DNAMAN was used to compare homologous sequences and analyze whether the mutation were highly conserved in the evolution of some species.Using HOPE to model homologous mutations at suspected pathogenic mutation to predict the potential changes in amino acid residues on protein function.A total of 100 patients with polydactyly or syndactyly without family historywere classified and summarized.Based on the results of questionnaires,Logistics regression model was used to analyze the correlation between clinical phenotype and environmental factors such as chemical drugs and virus infection.ResultsThe inheritance model of two family tree was in accordance with.the law of autosomal dominant inheritance(AD),due to the family tree showed that there were patients in each generation of the two families.Clinical data showed that all the patients in the two families had polydactyly.In family 1,the disease occurred in 3 generations,with consistent clinical symptoms and varying severity of the disease.Both hands of the proband’s grandfather were classified as PAP B.The father’s left hand wasclassified as PAP B.The proband’s right hand was classified as PAP,and his lefthand had cutaneous webbing between the 3rd and 4th fingers;his left foot had a well-formed digit on the fibular aspect.In family 2,the disease occurred in 4 generations.The proband’sboth hands wereclassified as PAP,the left foot was classified as PAP and PPD.The father of the proband had extra toes on the lateral side of the 5th toe of the right foot,and the 1st toe of both feet was obviously short.The proband’s great-grandmother,grandmother and aunt also were PAP.The verification results of WES and Sanger sequencing showed that there was a c.1622C>T(p.T541M)heterozygous mutation on the 11 th exon of GLI3 genein the family 1,which was a new mutation.In family 2,a deletion mutation c.2783 del G(p.Arg928Profs24X)was found on the 15 th exon of GLI3 in all patients.These gene variations haven’t been included in the databases or reported in the literatures.The genetic variations weren’t found in other normal members of the 2 families and 200 normal controls.The predicted result value of the point mutation by Poly Phen2 was 1.000 and the PROVEN predicted value was 0.000,which indicating that the gene mutation was pathogenic.The mutation was also conserved in the evolution of different species according to the result of DNAMAN.Protein structure prediction analysis showed that mutation c.1622C>T(p.T541M)of GLI3 gene caused the transformation of 541 st amino acid from threonine to methionine.Since the methionine was more hydrophobic than threonine.Moreover,the mutant amino acid is located near the zinc finger region of the protein,suggesting that this gene mutation may lead to changes in protein structure and function.The frame-shifting mutation c.2783 del G(p.Arg928Profs24X)carried by GLI3 gene was found in family 2,causing the disorder of the928 th amino acid of the protein encoded by GLI3 gene.There’re 89 cases of polydactyly and 11 cases of syndactyly in 100 cases of patiants.The incidence of all subtypes was consistent with the incidence reported clinically.After single-factor analysis of collected clinical data,there’re 8 factors including maternal fever during pregnancy,gestational hypertension,hyperglycemia,other complications,medication during pregnancy,gestational age higher than 30 years old,father’s paternal age higher than 35 years old,and paternal smoking were significantly correlated with the incidence of patiants.After establishing a Logistics regression analysis model,it was found that maternal infection during pregnancy and other complications such as gestational hypertension and hypertension,as well as paternal smoking was a high risk factor for the occurrence of sporadic congenital polydactyly and syndactyly.ConclusionsThe genetic models of both two families were AD.All the effected family members were PAP/PPD.The main pathogenic gene is GLI3.In this study,the heterozygous mutation c.1622C>T(p.T541M)was found on 11 st exon of GLI3 gene.This mutation hasn’t been described in the literaturesor included in the databases.This new mutation enriches the gene mutation spectrum of GLI3.In this study,the frame-shifted mutation c.2783 del G(p.Arg928Profs24X)was found on the 15 th exon of GLI3 gene.The mutation is a new mutation,which hasn’t been reported in relevant literatures or included in the databases.The studyfound that maternal infection during pregnancy and other complications such as gestational hypertension and hypertension,as well as the father’s smoking was a high risk factor for the occurrence of sporadic polydactyly and syndactyly,which should be avoided as far as possible.