Two percent of the residents of Bengkala, Bali, have profound, congenital, neurosensory, nonsyndromal deafness due to an autosomal recessive mutation at the DFNB3 locus. We have employed a direct genome-wide disequilibrium search strategy, allele-frequency-dependent homozygosity mapping (AHM), and an analysis of historical recombinants to map DFNB3 and position the locus relative to flanking markers. DFNB3 maps to chromosome 17, closest to D17S261, pRM7-GT and D17S805. In individuals homozygous for DFNB3, historical recombinant genotypes for the flanking markers, D17S122 and D17S783, place DFNB3 in a 5.3 cM interval of the pericentromeric region of chromosome 17 on a refined linkage map of 17p-17q12. Based on conserved synteny, the murine sh2 gene may be the homologue of DFNB3.

Waardenburg syndrome (WS) is a clinically and genetically heterogeneous disease accounting for >2% of the congenitally deaf population. It is characterized by deafness in association with pigmentary anomalies and various defects of neural crest-derived tissues. At least four types are recognized (WS1, WS2, WS3 and WS4) on the basis of clinical and genetic criteria. Two previously described families seemed to delineate a new subtype characterized by WS2 in conjunction with ocular albinism (OA). Since mutations in the MITF gene are responsible for some instances of WS2, we screened for mutations in one of the WS2-OA families and discovered a 1 bp deletion in exon 8 of MITF. OA previously has been associated with compound heterozygosity for a mutant TYR allele and the TYR(R402Q) allele, a functionally significant polymorphism that is associated with moderately reduced tyrosinase catalytic activity. In this family, all of the individuals with the OA phenotype are either homozygous or heterozygous for TYR(R402Q), and heterozyous for the 1 bp deletion in MITF This suggests that the WS2-OA phenotype may result from digenic interaction between a gene for a transcription factor (MITF) and a gene that it regulates (TYR).

Waardenburg syndrome (WS) type 1 is an autosomal dominant disorder characterized by sensorineural hearing loss, pigmentary abnormalities of the eye, hair, and skin, and dystopia canthorum. The phenotype is variable and affected individuals may exhibit only one or a combination of several of the associated features. To assess the relationship between phenotype and gene defect, clinical and genotype data on 48 families (271 WS individuals) collected by members of the Waardenburg Consortium were pooled. Forty-two unique mutations in the PAX3 gene, previously identified in these families, were grouped in five mutation categories: amino acid (AA) substitution in the paired domain, AA substitution in the homeodomain, deletion of the Ser-Thr-Pro-rich region, deletion of the homeodomain and the Ser-Thr-Pro-rich region, and deletion of the entire gene. These mutation classes are based on the structure of the PAX3 gene and were chosen to group mutations predicted to have similar defects in the gene product. Association between mutation class and the presence of hearing loss, eye pigment abnormality, skin hypopigmentation, or white forelock was evaluated using generalized estimating equations, which allowed for incorporation of a correlation structure that accounts for potential similarity among members of the same family. Odds for the presence of eye pigment abnormality, white forelock, and skin hypopigmentation were 2, 8, and 5 times greater, respectively, for individuals with deletions of the homeodomain and the Pro-Ser-Thr-rich region compared to individuals with an AA substitution in the homeodomain. Odds ratios that differ significantly from 1.0 for these traits may indicate that the gene products resulting from different classes of mutations act differently in the expression of WS. Although a suggestive association was detected for hearing loss with an odds ratio of 2.6 for AA substitution in the paired domain compared with AA substitution in the homeodomain, this odds ratio did not differ significantly from 1.0.

Bengkala is an Indonesian village located on the north shore of Bali that has existed for over 700 years. Currently, 2-2% of the 2185 people in this village have profound congenital deafness. In response to the high incidence of deafness, the people of Bengkala have developed a village specific sign language which is used by many of the hearing and deaf people. Deafness in Bengkala is congenital, sensorineural, non-syndromal, and caused by a fully penetrant autosomal recessive mutation at the DFNB3 locus. The frequency of the DFNB3 mutation is estimated to be 9-4% among hearing people who have a 17-2% chance of being heterozygous for DFNB3. (J Med Genet 1995;32:336-343) A medical and genetic analysis of deafness in Bengkala, Bali began in 1990 with the identification of deaf subjects and their relationships. An Bali.1-3 Goitre has been the concern of Indonesian physicians for many years and has been the subject of extensive regional iodide therapy since 1980.2 In addition to goitre, 47 of the residents of Bengkala are congenitally deaf. Fig 1 shows the families of all of the deaf people in Bengkala. It is suspected that the history of deafness in Bengkala spans many generations since virtually the entire population of Bengkala uses a village specific sign language as a means of integrating the deaf and hearing into a community. FAMILY HISTORIES AND ASSESSMENT OF DEAFNESSFamily histories and pedigrees were collected over a three year period and were used as a guide to interviews needed to obtain multiple independent confirmations of the hearing status, the time of onset of deafness, and the progression of hearing impairment for each deaf person.

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