9Genotype-specific CI outcomes

TA pattern by gene

Collecting the genotype-outcome reports and arranging them by expression site produces a clear pattern — the empirical face of the spiral-ganglion hypothesis. Good performers cluster among the membranous-labyrinth genes; variable and poor performers among the spiral-ganglion genes. Compare them below.[2012]

CThe good performers

GJB2 recipients perform at least as well as other implantees — the cochlear lesion spares the nerve (Module 4). SLC26A4 (pendrin, the Pendred / enlarged-vestibular-aqueduct gene) causes a membranous-labyrinth dysfunction and likewise implants well across reported series. OTOF (otoferlin) — despite causing auditory neuropathy — is a good performer because its lesion is pre-neural (Module 10). And mitochondrial deafness, which damages hair cells and the stria while sparing the ganglion, is also a good performer.[2002, 2006]

CThe variable: TMPRSS3

TMPRSS3is the instructive intermediate case. It is robustly expressed in the spiral ganglion, so the hypothesis predicts trouble — yet the published reports are genuinely mixed: some recipients do well, others poorly on the same word tests. TMPRSS3 is a reminder that “spiral-ganglion gene” does not mean “uniformly poor” — degeneration is a continuum, and outcome varies with how much functioning ganglion remains.[2014]

CThe poor: spiral-ganglion genes

At the unfavourable pole is DDON / TIMM8A — deafness-dystonia-optic-neuronopathy (Mohr-Tranebjærg) syndrome. Its temporal-bone histology shows degeneration of the spiral-ganglion neurons with the membranous labyrinth relatively preserved— the exact opposite of GJB2 — and, consistent with the hypothesis, implant performance is poor. It is the clearest human example of a gene that destroys the implant's target.[2012]

CSyndromic genes and variability

Some syndromic genes give variable results for an additional reason. In CHARGE syndrome (CHD7), inner-ear malformations and variable spiral-ganglion involvement combine with frequent cognitive and multisensory impairment, so outcomes scatter. The lesson is that genotype is one predictor among several — anatomy, neural survival, and the child's wider development all act alongside it.

CUsing it in clinic

Used carefully, the genotype-outcome map supports a more honest pre-operative conversation: optimism for a membranous-labyrinth gene, realism and a robust rehabilitation plan for a spiral-ganglion one — never a reason to withhold an implant, given the uncertainty (Module 11). One genotype, however, deserves its own module, because it looks alarming yet implants well: auditory neuropathy and OTOF (Module 10).