A significantly increased risk for dominant sensorineural deafness in patients who have Hirschsprung disease (HSCR) caused by endothelin receptor type B and SOX10 has been reported. Despite the fact that c-RET is the most frequent causal gene of HSCR, it has not been determined whether impairments of c-Ret and c-RET cause congenital deafness in mice and humans. Here, we show that impaired phosphorylation of c-Ret at tyrosine 1062 causes HSCR-linked syndromic congenital deafness in c-Ret knockin (KI) mice. The deafness involves neurodegeneration of spiral ganglion neurons (SGNs) with not only impaired phosphorylation of Akt and NF-κB but decreased expression of calbindin D28k in inner ears. The congenital deafness involving neurodegeneration of SGNs in c-Ret KI mice was rescued by introducing constitutively activated RET. Taken together with our results for three patients with congenital deafness with c-RET-mediated severe HSCR, our results indicate that c-Ret and c-RET are a deafness-related molecule in mice and humans. spiral ganglion neuron | syndromic congenital deafness | tyrosine kinase A bout 30% of the 120 million people worldwide who suffer from congenital (early-onset) hearing loss are syndromic, and the remaining 70% are nonsyndromic (1-3). To elucidate the etiologies for the hearing losses, inner ears have been morphologically investigated as one of the target tissues. The inner ears contain the organ of Corti and the stria vascularis. The stria vascularis serves to maintain the endolymph potential. The organ of Corti, which consists of two kinds of sensory cells (inner hair cells and outer hair cells) is responsible for mechanotransduction, by which sound impulses are converted into neural impulses. Auditory information from the sensory cells is transmitted to spiral ganglion neurons (SGNs) as the primary carrier, followed by eventual transmission to the auditory cortex (1, 2