However, consistent with previous observations [3] and irrespective of the age of onset, progression of disease was similar between NP-C siblings who shared the same haplotypes (Figure 1, Additional file 6: Figure S2), indicating that at least part of the variability in NP-C progression is associated with distinct NPC1- and NPC2-mutations. This evidence concerns the gene NPC2 and nasopharyngeal carcinoma.