Puberty is a remarkable time during adolescence when the body develops characteristics of a mature adult body, a dramatic increase in height, and becomes capable of reproduction. The mechanisms that signal to the body to commence pubertal onset remain largely unknown and is an important area of child health to better understand. Children affected by disorders of pubertal timing (e.g. central precocious or delayed puberty) are at increased risk for short- and long-term health consequences, including poorer heart health, metabolism, cancer risk, bone strength, and mental health. Mutations in genes in children affected by pubertal disorders provide windows into understanding the mechanisms of puberty and reproduction and can advance our options for diagnosing and treating pubertal disorders. In children with central precocious puberty, mutations in a gene, Makorin Ring Finger Protein 3 (MKRN3), an inhibitor of pubertal onset, is the most common genetic cause. The discovery of this gene was important in child health, as children previously diagnosed as having early puberty without an identifiable cause (e.g. idiopathic) were later found to have mutations in MKRN3. ~10% of individuals with CPP have mutations in MKRN3 and the likelihood of finding a mutation is even higher (~33-46%) when multiple family members have been affected. Given its importance as a cause of central precocious puberty, the aim of this study is to understand the impact of this important gene in children with delayed puberty, who may have mutations not yet identified. The aims of this proposal are to: 1) perform genetic analysis of a large cohort of children with delayed puberty for mutations in MKRN3 and 2) understand MKRN3’s mechanism of action using a novel, innovative mouse model that will overexpress Mkrn3 selectively in specialized neurons, called kisspeptin neurons, in one of the hormone centers of the brain. The proposed studies aim to change how we diagnose children with delayed puberty and also how, by using a mouse model to understand its mechanism of action. Manipulation of MKRN3 could have a role as a future therapeutic target, such as in children with central precocious puberty and other reproductive disorders, such as endometriosis.