Searching for digenic inheritance in deaf Brazilian individuals using the multiplex ligation-dependent probe amplification technique.

Mutations in the genes coding for connexin 26 (Cx26), connexin 30 (Cx30), and connexin 31 (Cx31) are the main cause of autosomal recessive nonsyndromic sensorineural hearing loss (AR-NSNHL). The 35delG mutation is the most frequent in the majority of Caucasian populations and may account for up to 70% of all GJB2 mutations. As a large number of affected individuals (10%-40%) with GJB2 mutations carry only one mutant allele, it has been postulated that the presence of additional mutations in the GJB6 gene (Cx30) explains the deafness condition found in these patients. In the present study, we screened the c.35delG mutation in ~600 unrelated Brazilian patients, with moderate to profound AR-NSNHL. Other point mutations in the coding region of the GJB2 gene were screened by sequencing analysis as well as the IVS 1+1 G>A splice site mutation in the same gene. Digenic mutations including large deletions and duplications were investigated in the Cx26, 30, and 31 genes in monoallelic individuals for mutations in the GJB2 gene. Large deletions and duplications were assessed by multiplex ligation-dependent probe amplification. We found 46 patients with mutations in only one GJB2 allele. Different pathogenic mutations associated with c.35delG were found in 13 patients. Two patients were identified with digenic heterozygous mutations. Our findings contributed to more accurate diagnosis and more appropriate genetic counseling in 28% of patients studied (13/46).

Newborn hearing screening and genetic testing in 8974 Brazilian neonates.

OBJECTIVE: An early diagnosis has been a priority in the audiological practice. Identifying hearing loss until 3 months old through Universal Newborn Hearing Screening and intervention before 6 months old, minimize the impact of auditory loss in the health and communication development of these children. However, in the clinical practice, despite the help of the risk indicators in the audiological and etiological diagnosis, the integrated services have come up against the challenge of determining the causes of auditory loss, bearing in mind that approximately 50% of the subjects who have congenital loss do not show risk factors in their clinical history. The current research aims introduce together etiologic and audiological diagnosis of newborns. METHODS: We eluted dried blood spots from paper and performed genetic testing for 35delG mutation in 8974 newborns that were also screened for transient otoacoustic emissions (TOAE). In addition, the A1555G and A827G mutations in the MTRNR1 mitochondrial gene were screened in all newborns. RESULTS: We have found 17 individuals who failed in TOAE. Among them, we detected 4 homozygous newborns for 35delG mutation and 3 individuals with A827G mutation in the MTRNR1 mitochondrial gene. The frequency of 35delG carriers was 0.94% [84/8974]. In all 17 individuals who failed in OAE no other mutation besides those mentioned above was found. CONCLUSIONS: The results greatly contribute to the public health area indicating the etiologic diagnosis, allowing family counseling as well as the early rehabilitation treatment or surgical intervention. Over time that will help to reduce the costs of rehabilitation considerably.