AQP5 and Hyperkeratosis: The severe clinical findings in affected PPK2 family members could possibly be a combined effect of variants AQP5 (NM_001651.4): c.103T>G (p.(Trp35Gly)) and FLG (NM_002016.2): c.1501C>T (p.(Arg501Ter)), which co-segregate with hyperkeratosis in the family.