Figure 2. Distribution of the age of PRA onset in sporadic MLHD cases. Presented are 48 sporadic PRA cases of MLHDs from the Japanese pet population. These are shown according to the age of onset. The dogs were already blind at the time of presentation and the age of onset was determined by the earliest possible sign of visual impairment noticed by the owner. An additional 11 sporadic PRA cases from Japan, used for mapping purposes, are not shown here since the information on the age of onset was uncertain or unknown. RPGRIP1 genotypes are denoted as follows: wildtype homozygote (+/+); heterozygote (+/−); insertion homozygote (−/−).