Interdisciplinary care in disorders/differences of sex development (DSD): The psychosocial component of the DSD—Translational research network / What is Kallman syndrome, or hypothalamic hypogonadism?

The suffix “hypo” means “under.” When it is used in medical terminology, it usually means that an organ is producing levels lower (under) the normal range. “Hypogonadism” therefore signals a condition in which a person’s sex hormone levels are lower than the normal range.

The hypothalmus is a region of the brain that can affect levels of sex hormone production. “Hypothalamic hypogonadism” therefore means that, because the hypothalmus is working differently than usual, a person is producing lower levels of sex hormones than usual. Hypothalamic hypogonadism is also called “Kallman syndrome.” It is more commonly found in males (XY) than females (XX).

Usually Kallman syndrome is congenital, which means that it is present from fetal development onward. The low level of sex hormones results in atypical sex development, including a delayed puberty. Males with Kallman syndrome are typically born with small penises and undescended testicles (called cryptorchidism).

Kallman syndrome also involves a decreased or absent ability to smell. (A lowered sense of smell is called hyposmia, and the absence of a sense of smell is called anosmia.) In rare cases, a person can develop hypothalamic hypogonadism after puberty.

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