MTHFR and obesity due to melanocortin 4 receptor deficiency: Of the eleven genes most important for their quantitative contribution to maintain the flow of carbon units through 1CM in the liver (MAT1A, AMD1, GNMT, PEMT, GAMT, AHCY, CBS, BHMT, MTR, MTHFR, and SHMT1/2), the mRNA content of six of them—catalyzing SAMe synthesis (MAT1A) and catabolism (GNMT), homocysteine synthesis (AHCY), and remethylation (BHMT, MTHFR)—and the first step in the transsulfuration pathway (CBS) is lower among obese NASH patients compared to individuals with metabolically healthy obesity (MHO), while obese NAFL subjects are intermediate between MHO and NASH patients [43,44].