Any genetic defects that actually serve a purpose?

Do you know of any interesting genetic defects in humans which could actually have benefits?

This is super interesting, but did you know that humans were supposed to actually be lactose intolerant? Therefore, lactose tolerance is the anomaly here.

Humans didn’t used to have the ability to digest lactose (a sugar in dairy products). Not sure if this is accurate but 2 thirds of the world cannot tolerate milk as adults (especially in Eastern societies). Children usually stop producing lactase (the digestive enzyme) around the age of 5, which subsequently makes dairy harder to process.

Around 12.000 years ago in Turkey there was a man who was born with his lactase producing gene without an off switch. He then passed this to his children who then passed it on and so it spread. This gene spread across Europe, while a few random mutations popped up in other parts of the world around the same time.

Cool genetic mutation anyway.

From wiki:

X-linked agammaglobulinemia

XLA is a rare genetic disorder, which is characterized by the complete loss of IgG antibodies in patients. Because IgG antibody is a vital constituent of humoral immunity, patients with XLA have severe deficiency in humoral immunity. Because of it, XLA patients make ideal subjects for studying the role humoral immunity plays in fighting infections.

XLA was originally identified by Dr. Bruton in 1952. Its cause was later identified (1993) as a defect occurring in a kinase, which was named as the Bruton’s tyrosine kinase (Btk), in honor of Dr. Bruton. Btk is very vital to B cell development, and loss of its function results in total inability of producing IgG antibodies.

Btk was soon identified as an vital protein in a number of B cell malignancies including chronic lymphocytic leukemia (CLL) and mantle cell lymphoma, which led to the development of the “magic bullet” Btk inhibitors, such as Ibrutinib and Acalabrutinib. In a phase III trial, Acalabrutinib achieved a 95% response rate in CLL. So you can see how a severe disease led us to a cure for another life-threatening disease.

Low (or no) levels of melanin

Pale skin which contains less melanin by scientific bases doesn’t have many advantages (higher rates of skin cancer, you burn easier etc.). In the western world, however, in a social context white skin has the “benefit” of being seen as a beauty standard. And not only here, in Asia too, women work hard to lighten their skin, which is so weird to me. It’s gotten to a point where low levels of melanin (therefore higher levels of sun damage) is a beauty ideal. Lack of melanin also gives blue or green eyes (essentially not brown or black), lighter hair - white, blonde, light brown. These are all beauty ideals that come from recessive genes - in this case low levels of melanin.