SPP2 and vision disorder: In subject N, exome sequencing targeting gene panels for vision disorders and hearing impairment initially identified a heterozygous SPP2 (OMIM 602637 ̧ isolated RP (Liu et al. 2015)) variant (NM_006944.3:c.439G > A NP_008875.1:p.(Glu147Lys)) and a possibly explanatory heterozygous MCM2 (OMIM 116945, isolated SNHL OMIM 616968 (Gao et al. 2015)) variant (NM_004526.4:c.547C > T NP_004517.2:p.(Arg183Cys)).