PEX6 and Usher syndrome: This may reflect the relatively mild ZSSD phenotype seen in HS patients, which may have led to misdiagnosis as Usher syndrome, or simply the private nature of many mutations in ZSSD.30 By contrast, the missense variant c.1802G>A, p.(R601Q) (rs34324426) has been identified in three of the families detailed here and therefore in four out of the seven HS families with PEX6 mutations reported to date.