I'll look at that study you mentioned, thank you.
https://www.nejm.org/doi/full/10.1056/NEJM199909163411204
There is more information about the family involved out there, but I can't remember where I read about it.
A thing I found interesting about the genetics of hunger, is the concept of mongenetic, v polygenetic traits Monogenetic traits - a variation in a single gene is has an observed often severe impact. Polygenetic traits - variations in a large number of genes and environmental are contributing In reality these traits exist on a spectrum of severity. The more sublte the impact of a gene the more people you need to study to tease out the influence of the gene, so monogenetic traits tend to be discovered first.