The Genetic Testing Of Three Waardenburg Syndrome Type â…¡ Families

Waardenburg syndrome(WS), also called auditory-pimentary syndrome, is a clinical syndrome mainly manifesting such clinical features as congenitally sensorineural hearing loss, abnormal iris color, forehead leukotrichia or leukotrichia in a young age(<30years old), and abnormal skin pigment distribution. Addition to these typical manifestations, other possible physical signs could be inner canthus displacement, skeletal muscle dysplasia, gastrointestinal tract anomalies including Hirschsprung’s discase (HSCR), gastrointestinal tract atresia or defects in the nervous system. WS is one of the most frequently encountered syndromic deafness in clinics. Statistically, the incidence of WS is about1.44-2.05/100000in general population and2-5/100in the population of congenital hearing impairment. Up to now, six gene mutations was proved underlying the genesis of WS, which are PAX3, MITF, SOX10, SNAI2, EDN3, and EDNRB. Among these genes, MITF and SNAI2are related to WS type Ⅱ, PAX3is related to type Ⅰ and Ⅲ, SOX10is related to type Ⅱ and Ⅳ, the rest two are related to type Ⅳ.Purpose:Through the thorough investigation of three Waardenburg syndrome type Ⅱ families, including to classify clinically and to test the candidate gene such as MITF, SOX10, SNAI2, we try to work out the genetic rules of the mutated genes which related to Waardenburg syndrome type Ⅱ.Methods:We identified three children with WS type Ⅱ who resort to the Department of Otorhinolaryngology-Head&Neck Surgery of Second Xiangya Hospital for cochlear implantation. These three children come from three different families and the basic clinical information of their family members and relatives within three generations were collected carefully. They also undertook thorough physical examinations and the corresponding families were clinically classified to the type they belong to. Classical genetic maps of each family were plotted using Pedigree(PED). All the subjects signed the informed consent form before their peripheral venous blood samples were collected. Then, all the exons located in the coding region of the candidate genes(PAX3, MITF, SOX10, SNA12) were proliferated by polymerase chain reaction(PCR). Using automatic sequencer, sequencing was performed both forwardly and backwardly to the enzyme-digested products obtained by PCR. The data was analyzed using Gene Tool and the relevant information on molecular biological websites.Results:1. Based on the propositi of the three families as well as the clinical manifestation and relevant clinical data of other family members suffering the disease, WS type Ⅱ was verified for all of the three families.2. Through the testing of candidate genes including MITF, SOX10, SNAI2, PAX3, the propositi of family one, such as Ⅳ:1,Ⅱ:5,Ⅲ:7,Ⅲ:9, were found a mutation located in the No.7exon of MITF, namely C.649-651del AGA, which cause the missing of arginine in217th site of the amino acid chain. This mutation have been reported domestically and internationally. For family one, there were no mutations detected in SOX10, SNAI2, PAX3, while for the rest two families, no mutations were detected in all of the four candidate genes.Conclusions:1.This study collected all the useful clinical data from three WS families, plot the genetic maps of each family, made a clinical type classification, as well as tested the relevant genes using molecular biological methods, then put our knowledge for this kind of disease further forward.2. We found a mutation located in the No.7exon of MITF, namely C.649-651del AGA in first family. It would be promising theoretically for the prenatal disgnosis.3. No mutations were detected in all of the four candidate genes for family two and family three, suggesting there could be hidden genes with mutations or mutations in unknown sites of the already-known genes. Both kind of mutations are undetectable using current testing methods and need further exploration...