Rare IR-related entities include different types of congenital or acquired lipodystrophy syndromes (Berardinelli–Seip syndrome), mutations of insulin receptors (type A IR syndrome, leprechaunism or Donohue syndrome, and Rabson–Mendenhall syndrome), or other genetic disorders such as Alstrom syndrome, SOFT syndrome, MARFAN syndrome, and monogenetic obesity with underlying melanocortin-4 receptor (MC4R) gene mutations [11,12,13,14,15,16,17,18]. This evidence concerns the gene MC4R and Leprechaunism.