PEX1 and peroxisomal disease: HS is a formof peroxisomal biogenesis disorders and has been found to involve biallelicvariations in peroxismal biogenesis factors 1 (PEX1) and 6(PEX6).[136]HS was first described by Heimler et al in a brother and sister who presented withSNHL, enamel hypoplasia, and nail abnormalities.[137] Few cases have been reported to date; however,Mechausseir et al propose that HS is most likely underdiagnosed due to misdiagnosisof enamel defects.[136]Ophthalmologic manifestations of HS include RD, which can present retinitispigmentosa and macular degeneration.