Number and caliber of axons in the sciatic nerve from wild-type and AIP mice injected with different doses of rAAV2/8-hPBGD. The number of degenerated axons [(a) female, (b) males] and the mastocyte counts [(c) females, (d) male] were measured in light micrographs sections (see Supplementary Materials and Methods) of sciatic nerves from mice 90 days after respective dose of gene therapy. Mastocyte cells were readily differentiated based upon morphological criteria and the presence of metachromatic granules. (e) Axon density and percentage of large axons were also measured in the same animals. The results obtained with different rAAV2/8 doses are statistically compared to the baseline level in the AIP group (&P < 0.05; &&P < 0.01) and also to the wild-type animals (*P < 0.05; **P < 0.01) using the nonparametric Mann–Whitney test. AIP, acute intermittent porphyria; rAAV, recombinant adeno-associated virus; WT, wild type.