CTH and early-onset autosomal dominant Alzheimer disease: H2S, as an endogenous molecule produced by the enzymatic activity of CTH, CBS, or MPST, is the main regulator of post-translational S-sulfhydration (persulfidation) of proteins that has been reported, e.g., in aging, Alzheimer’s disease, or the cardiovascular system [33,34,35,36,37,42].