Cartilage Hair Hypoplasia

What does the name mean?

Cartilage Hair Hypoplasia (CHH) is also known as metaphyseal dysplasia, McKusick type. The disorder was recognized as a clinical entity in 1965, when Victor McKusick and colleagues described the condition in an inbred Amish population (1). The term “metaphyseal” relates to the metaphysis, which is the wide region located at the ends of long bones. The name “Cartilage Hair Hypoplasia” was coined due to the characteristic features: fine, sparse hair and cartilage abnormalities.

How common is Cartilage Hair Hypoplasia?

Cartilage Hair Hypoplasia is a relatively rare congenital disorder. It is most prevalent among the Old-world Amish and Finnish populations. Among Amish people, the incidence is approximately 1.5 in 1000 live births, whereas in Finland, it is 1 in 18,000 to 23,000 (2). 

Is Cartilage Hair Hypoplasia inherited?

Cartilage Hair Hypoplasia is typically inherited in an autosomal recessive manner (2).

What causes Cartilage Hair hypoplasia?

This dysplasia is caused by a mutation of the gene encoding the RNA component of the ribonuclease mitochondrial RNA processing complex (RMRP). The locus of the RMRP gene is on chromosome 9p13. The mutation affects cartilage development.

• What are the physical characteristics of Cartilage Hair Hypoplasia?
• How is the diagnosis made?
• Problems in the musculoskeletal system
• Problems elsewhere in the body
• What are things to watch out for?
• References