Our results are in agreement with the general assessment that the amount and residual cholesterol transport capacity of mutant NPC1 are major predictors of clinical severity; however, a number of patients with an adult-onset neurological disease whose fibroblasts display a severe block of lysosomal cholesterol egress have been described (e.g. some homozygotes for p.I1061T, patients #15, 17, 23, 24 in the Nadjar et al. study, [39] and patient 2 in Table 5 in [3]), that would require further investigations. Here, NPC1 is linked to Adult onset.