Why is CHH Common in Amish & Finnish Populations?

Cartilage-hair hypoplasia (CHH)—a rare genetic disorder characterized by short stature, fine sparse hair, and immune system abnormalities—is much more common in Old Order Amish and Finnish populations because of a genetic phenomenon known as the founder effect ^[1]. CHH is an autosomal recessive genetic condition caused by mutations in the RMRP gene ^[2]. For a child to inherit an autosomal recessive condition, both parents must carry a copy of the mutated gene and pass it on. In large, diverse populations, the chance of two people with the exact same rare gene mutation having children together is very low. However, in communities with a shared, isolated ancestry, the chances are much higher ^[3][4].

What is the Founder Effect?

The founder effect occurs when a small group of individuals breaks off from a larger population to establish a new, isolated community ^[1]. The new community’s genetic makeup is determined largely by those few “founders” ^[3].

If one of the original founders happened to carry a rare genetic mutation—such as a specific “spelling mistake” in the RMRP gene that causes CHH—that mutation will be passed down to their descendants ^[5][6]. Over generations, because members of the Old Order Amish and Finnish populations have historically married within their own communities, that specific genetic variant became much more concentrated than it is in the general population ^[4][2].

Can People of Other Backgrounds Get CHH?

Yes. While CHH is diagnosed most frequently in individuals of Amish and Finnish descent, a child of any ethnic background can be born with CHH ^[7][5].

Because the RMRP gene can mutate in different ways, researchers have identified cases of CHH in diverse populations worldwide, including individuals of Japanese, Korean, Indian, Moroccan, and Brazilian descent ^[8][9][10]. In fact, other populations may have their own unique founder effects for different variations of the RMRP gene ^[5][6].

If your family does not have Amish or Finnish heritage, your child can still have CHH if both parents happen to be carriers of an RMRP gene mutation.

Next Steps and Carrier Testing

If you have a family history of CHH, or if you belong to a population where the condition is more common, you may choose to discuss genetic carrier screening with your doctor or a genetic counselor. This testing can help determine if you and your partner carry the gene mutation associated with CHH, giving you the information you need to make informed decisions for your family.