They include: (i) congenital MGD, because no mutations have been identified so far in the putative disease gene MGAM in affected patients, suggesting that the disease may depend on other regulatory genes [27]; (ii) FM, in which more genes encoding fructose carriers may be involved [17]; (iii) CSD, in which only syndromic forms have mutations in the SPINT2 gene [38]; (iv) IPEX-like syndrome, for which the disease gene is still unknown even if a single patient had a mutation in the CD25 encoding gene [52]. The gene discussed is MGAM; the disease is immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.