Cochlear implant surgery in patients with otosclerosis can be challenging, with a relatively high number of partial insertions and misplacements of the electrode array demanding revision surgery. A very high proportion of patients experienced facial nerve stimulation mainly caused by the distal electrodes. This must be discussed with patients preoperatively.

This study supports the finding in previous studies that no hypersalivation exists in children with CP who drool. Dysfunctional oral motor control seems to be responsible for saliva overflow from the mouth, whereas increased unstimulated salivary flow may occur in children with dyskinetic CP as a result of hyperkinetic oral movements.

Viewing the patients from this study and patients from a review of the literature concerning cochlear implantation in children with malformed inner ears including severe cochlear malformations, the occurrence of an aberrant facial nerve was 17%, which increases to 27% if one reviews the surgical findings in children with severe malformed cochleae such as a common cavity or a severe cochlear hypoplasia. In the latter patients, results in speech perception vary. Although the result of cochlear implantation may be promising, as in our patient with a common cavity, during preoperative counseling the child's parents must be informed that the result is uncertain.

In a Dutch consanguineous family with recessively inherited nonsyndromic hearing impairment (HI), homozygosity mapping combined with whole-exome sequencing revealed a MPZL2 homozygous truncating variant, c.72del (p.Ile24Metfs22). By screening a cohort of phenotype-matched subjects and a cohort of HI subjects in whom WES had been performed previously, we identified two additional families with biallelic truncating variants of MPZL2. Affected individuals demonstrated symmetric, progressive, mild to moderate sensorineural HI. Onset of HI was in the first decade, and high-frequency hearing was more severely affected. There was no vestibular involvement. MPZL2 encodes myelin protein zero-like 2, an adhesion molecule that mediates epithelial cell-cell interactions in several (developing) tissues. Involvement of MPZL2 in hearing was confirmed by audiometric evaluation of Mpzl2-mutant mice. These displayed early-onset progressive sensorineural HI that was more pronounced in the high frequencies. Histological analysis of adult mutant mice demonstrated an altered organization of outer hair cells and supporting cells and degeneration of the organ of Corti. In addition, we observed mild degeneration of spiral ganglion neurons, and this degeneration was most pronounced at the cochlear base. Although MPZL2 is known to function in cell adhesion in several tissues, no phenotypes other than HI were found to be associated with MPZL2 defects. This indicates that MPZL2 has a unique function in the inner ear. The present study suggests that deleterious variants of Mplz2/MPZL2 affect adhesion of the inner-ear epithelium and result in loss of structural integrity of the organ of Corti and progressive degeneration of hair cells, supporting cells, and spiral ganglion neurons.

Although the decision to implant should consider individual ear differences and other factors that might apply to a particular case, based on our data, all patients with preoperative scores of either 80% (phonemes correct) or 60% (words correct) and lower in an optimal-aided situation are potential candidates for a cochlear implant, provided that their preoperative speech perception score decreases below 50% (phonemes correct) or 20% (words correct), when background noise is added at a +5 dB signal to noise ratio.