Having a mutant LHCGR gene leads to what doctors now call familial male-limited precocious puberty, an extremely rare disease that affects only men because you have to have testicles, which is why it’s also called testotoxicosis. The condition tricks the testicles into thinking the body is ready to go through puberty — so wham, the floodgates open and the body is saturated with testosterone. The result is premature everything: bone growth, muscle development, body hair, the full menu of dramatic physical changes that accompany puberty. Only instead of being 13, you’re 2.