What Is Cartilage-Hair Hypoplasia? Cartilage-hair hypoplasia (CHH), caused by mutations in the RMRP gene, is an inherited disorder of bone growth that causes an individual to have short stature and other skeletal abnormalities. Individuals with CHH also tend to have fine, sparse hair and abnormal cartilage. Some individuals with CHH have an impaired immune system, leaving them more susceptible to infection, notably to a severe course of chicken pox. Anemia, a lowered number of red blood cells leading to fatigue and weakness, is common in children with CHH, though it usually disappears by adulthood. Some individuals may also have low levels of certain white blood cells. Individuals with CHH are at a higher risk for certain cancers, including non-Hodgkin's lymphoma and skin cancer. Symptoms and their severity vary widely among people with the disease. How Common Is Cartilage-Hair Hypoplasia? CHH is a rare disorder and is most common among the Amish population. One study indicated that 1 in 19 Amish were carriers of the disease and 1 in 1,340 Amish babies were born with the disease. It is also more common in the Finnish population, where 1 in 76 Finns is a carrier and 1 in 23,000 babies have the disease. How Is Cartilage-Hair Hypoplasia Treated? There is currently no treatment for CHH. There are drugs available that can be useful to treat chicken pox. Infections, particularly those in childhood, should be given close medical attention and those with extreme immunodeficiency may want to consider bone-marrow transplantation to ameliorate this symptom. Growth hormones can be considered for some patients. What Is the Prognosis for an Individual with Cartilage-Hair Hypoplasia? Individuals with CHH can live a normal lifespan. Those with severe immunodeficiency need to monitor their health more closely. Opportunistic infections can be fatal, particularly in childhood. Other names forcartilage-hair hypoplasia CHH Cartilage-hair hypoplasia McKusick type metaphyseal chondrodysplasia References Mäkitie et al., 2015, https://www.ncbi.nlm.nih.gov/books/NBK84550/ OMIM: Online Mendelian Inheritance in Man, OMIM [250250], 2017, https://www.omim.org/entry/250250 Ridanpää et al., 2001, Cell, 104(2):195-203, PMID: 11207361 Thiel et al., 2007, Am J Hum Genet, 81(3):519-29, PMID: 17701897 Thiel et al., 2011, Best Pract Res Clin Endocrinol Metab, Feb 25(1):131-42, PMID: 21396580