Identification of auditory genes and regulatory elements using a cytogenetic approach

Investigation of individuals with apparently balanced chromosomal rearrangements and major congenital anomalies has been a powerful method for discovery of genes causing various disorders. Using high resolution cytogenetic techniques, candidate genes disrupted or dysregulated by the rearrangement breakpoints can be rapidly mapped. Further study of these genes in other affected individuals or through animal models can then be used to validate their possible pathogenic effects. In an effort to identify novel genes involved in auditory function, we have ascertained individuals with hearing loss and apparently balanced chromosomal rearrangements. To illustrate the utility of this approach, I present three cases. In the first case, mapping the breakpoints of a t(2;13)(p24;g21) in an individual with profound sensorineural deafness revealed a novel gene, FLJ21820 , disrupted by the translocation. RNA in situ hybridization experiments showed that the gene is expressed in the hair cells, stria vascularis, limbus, and spiral ganglion of the inner ear suggesting it may be a deafness gene. Generation of a mouse model is currently in progress to verify the role of this gene in the auditory system. For the second case, an inv(7)(g21.3q35) segregating with hearing loss and craniofacial defects in a family with five affected members is interpreted to disrupt tissue-specific expression of the nearby DLX5 and DLX6 genes. Transgenic mouse experiments suggest that a 5115 bp sequence deleted at the 7g21.3 breakpoint contains an enhancer necessary for proper expression of DLX5 and DLX6 in the ear and developing bones. In the third case, molecular cytogenetic analysis of an individual with an inv(5)(g15q33.2) and profound sensorineural deafness revealed cryptic deletions associated with the breakpoints that result in the complete removal of NR2F1 from the inv(5). Haploinsufficiency for NR2F1 is the likely cause of the patient's deafness and many of the other associated anomalies based on striking similarity with the Nr2f1 null mouse. These results confirm the value of cytogenetic-based approaches for discovery of novel genes and regulatory elements essential for auditory development and function.