Hearing impairment is a common sensory deficit with both genetic and environmental aetiologies. Pre-lingual hearing loss affects approximately 1 in every 1000 children in the United States with a genetic basis in about 50% of the cases.¹ An additional 1 per 1000 individuals experience auditory deficits prior to adulthood.¹ Large pedigrees with monogenic non-syndromic hearing impairment have allowed genetic mapping of at least 80 chromosomal locations harbouring auditory-related deafness (DFN) loci with the identification of over 30 DFN genes.² The DFN inheritance pattern is designated by A dominant, B recessive, and M modifier, with a number following A, B, or M indicating the relative order in which the locus was identified. For example, DFNA1 represents the first dominantly inherited deafness locus mapped in humans.

Several myosin gene products have been implicated in hearing loss. Myosins constitute a family of motor proteins playing roles in diverse biological events such as muscle contraction, cell adhesion, organelle translocation, cytokinesis, and cell movement.^3,4 Myosin proteins share a conserved globular head domain with actin- and ATP-binding sites joined to varied amino and carboxy-terminus regions that determine the unique cellular role of each motor protein. For example, the Drosphila phototransduction NINAC (neither inactivation nor afterpotential C) protein couples a myosin head with a N-terminal kinase domain.⁵ The first myosin discovered, myosin-II, was isolated from muscle and shown to form myosin filaments by association of bipolar tail domains.³ Myosin-II has historically been referred to as a conventional myosin. Unconventional myosins do not form filaments and constitute a large rapidly-growing group of proteins.⁶ Mutation of one conventional myosin, non-muscle myosin, heavy polypeptide 9 (MYH9),⁷ and five unconventional myosins, myosin IA (MYO1A),⁸ myosin IIIA (MYO3A),⁹ myosin VI (MYO6),¹⁰ myosin VIIA (MYO7A) …