HP and Menkes disease: Taking into account their associations with inflammation (Kamma et al., 2004; Looh et al., 2022; Miao et al., 2022), in addition to our results of elevated FABP2 levels and a positive correlation between abundance of Bifidobacterium and zonulin across all of the MD cases, these findings are relevant given the literature on systemic inflammation resulting from gut barrier compromise and its role in MD development (Arneth, 2018; Peirce and Alviña, 2019; Simpson et al., 2021).