In MPSIIIA, it is known that a lack of lysosomal enzyme N‐sulfoglucosamine sulfohydrolase (SGSH), which degrades the complex sugar heparan sulphate (HS), results in a progressive clinical disease, characterised by hyperactivity and other behavioural abnormalities, developmental regression and cognitive decline (Wraith, 2002; Heron et al, 2011; Valstar et al, 2011; Wijburg et al, 2013; Shapiro et al, 2016). This evidence concerns the gene SGSH and Mental deterioration.