INPP5E and retinal degeneration: Of the 19 known pathogenic variants present in a homozygous state only three (p.[(Ser249Phe); (Arg596Thr)], p.(Val465Ile), p.(Arg621Trp)) resulted in a non-syndromic retinal degeneration, which may imply a hypomorphic or photoreceptor-specific impact of these variants on INPP5E function.