Prader-Willi Syndrome

Prader–Willi syndrome (PWS) is a condition that - in some cases - may be considered an intersex condition, although many would say it causes intersex conditions rather than being one in of itself. Prader-Willi syndrome affects an estimated 1 in 10,000 to 30,000 people worldwide.

This condition can cause hypogonadism and underdeveloped genitals (in both CTF and CTM individuals) within the people it effects, putting them on the intersex spectrum.

Those with this condition often have weak muscle tone (hypotonia), feeding difficulties, poor growth, delayed development, speech delay, crossed eyes, poor physical coordination, infertility, sparse pubic hair, short stature, a narrow forehead, almond-shaped eyes, a down-turned mouth, small hands and feet, fair skin, light hair, and delayed or incomplete puberty. They also typically have an insatiable appetite which causes overeating and obesity. Typically, one with this condition develops type two diabetes.

Sleep abnormalites, behavioral problems, outbursts, and compulsive habits are also common with those who have this condition.

Causes
Normally, a fetus inherits an imprinted maternal copy of PW genes and a functional paternal copy of PW genes. Due to imprinting, the maternally inherited copies of these genes are virtually silent, and the fetus therefore relies on the expression of the paternal copies of the genes. In PWS, however, there is mutation/deletion of the paternal copies of PW genes, leaving the fetus with no functioning PW genes, and causing this condition and its symptoms.

Resources

 * https://medlineplus.gov/genetics/condition/prader-willi-syndrome/#frequency
 * https://en.wikipedia.org/wiki/Prader%E2%80%93Willi_syndrome