Deafness, Autosomal Recessive 84a

A number sign (#) is used with this entry because autosomal recessive nonsyndromic hearing loss-84A (DFNB84A) can be caused by homozygous mutation in the PTPRQ gene (603317) on chromosome 12q21.

A form of autosomal recessive nonsyndromic deafness designated DFNB84B (614944), which also maps to chromosome 12q21, is caused by mutation in the OTOGL gene (614925).

Clinical Features

Schraders et al. (2010) reported 2 unrelated families with autosomal recessive sensorineural hearing loss and vestibular dysfunction. In a Dutch family, 2 adult sibs had bilateral, symmetric, sensorineural, hearing loss that was likely congenital. Neither patient developed normal speech, and both reported progression of hearing loss from severe to profound from 30 and 45 years of age and after, respectively. In addition, both reported delayed motor development. The second consanguineous Moroccan family had 2 affected sibs with bilateral, symmetric, sensorineural, progressive, and likely congenital hearing loss. Electronystagmography in caloric and rotary testing in both families demonstrated impaired vestibular function.

Mapping

In 2 consanguineous Palestinian families with autosomal recessive nonsyndromic hearing loss, Shahin et al. (2010) found linkage to a 12.5-Mb region on chromosome 12q (lod score of 3.45), designated DFNB84.

Molecular Genetics

In affected members of 2 unrelated families with autosomal recessive nonsyndromic sensorineural hearing loss with vestibular dysfunction (DFNB84A), Schraders et al. (2010) identified respective homozygous mutations in the PTPRQ gene (603317.0001 and 603317.0002).

Animal Model

Goodyear et al. (2003) showed that Ptprq localized to inner-ear hair bundles in chick inner ear and to kidney glomeruli. In early postnatal mice, Ptprq stained hair bundles in the cochlea and the vestibule in the inner ear and was also expressed during embryonic development. The distribution of staining on hair bundles differed according to the type of hair cell and its location. Two different transgenic mouse strains with different mutations in the Ptprq gene had absence of shaft connectors in mutant vestibular hair bundles and misaligned or absent stereocilia. Mutant mice showed rapid postnatal deterioration in cochlear hair-bundle structure, associated with smaller than normal transducer currents, progressive loss of basal-coil cochlear hair cells, and deafness. Goodyear et al. (2003) suggested that Ptprq is required for formation of the shaft connectors of the hair bundle, the normal maturation of cochlear hair bundles, and the long-term survival of high-frequency auditory hair cells.