FZD4 and cerebellar degeneration: Consistent with near-complete loss of Norrin-FZD4 signaling observed in our proband, Fzd4−/− knockout mice display congenital retinal hypovascularization similar to that observed in FEVR, as well as progressive inner-ear vascular atrophy resulting in hearing loss and progressive cerebellar degeneration. Alternatively, formally testing the parents for hearing loss and a broader genetic search beyond the AUDIOME panel may reveal a separate etiology for the patient’s auditory deficit.