The system regulates the bodies metabolism growth and functions of the sexual organs

The endocrine system

“Genes and environmental effects are often part of the explanation. “

“...disease-causing alleles of one gene may be suppressed by alleles of another gene elsewhere in the genome, or a person's overall health may influence the strength of a disease phenotype.”

https://www.khanacademy.org/science/high-school-biology/hs-classical-genetics/hs-non-mendelian-inheritance/a/polygenic-inheritance-and-environmental-effects