For individuals negative for this streamlined testing with phenotypes similar to PWS with obesity, an expanded panel of genes can be considered to test diseases recognized as syndromic obesity syndromes, such as Alstrom, Bardet–Beidel, Cohen, Carpenter, Kabuki, WAGR, or Fragile X, or monogenic causes (e.g., LEP, LEPR, BDNF, FTO, SH2B1, POMC, MCR4, TUB, AGRP, UCP1, CART, NEGR1, and PPARG) (e.g., Bell et al., 2005; Choquet and Meyre, 2010; Butler, 2016; Kaur et al., 2017). This evidence concerns the gene CARTPT and Down syndrome.