|Classification and external resources|
Cartilage–hair hypoplasia (CHH), also known as McKusick type metaphyseal chondrodysplasia,:578 is a rare genetic disorder. It is a highly pleiotropic disorder that clinically manifests by form of short-limbed dwarfism due to skeletal dysplasia, variable level of immunodeficiency and predisposition to malignancies in some cases. It was first reported in 1965 by McKusick et al. Actor Verne Troyer is affected with this form of dwarfism, as was actor Billy Barty, who was renowned for saying "The name of my condition is Cartilage Hair Syndrome Hypoplasia, but you can just call me Billy."
CHH is an autosomal recessive inherited disorder. A rarely encountered genetic phenomenon, known as uniparental disomy (a genetic circumstance where a child inherits two copies of a chromosome from one parent, as opposed to one copy from each parent) has also been observed with the disorder.
An association between mutations near or within the ncRNA component of RNase MRP, RMRP, has been identified. The endoribonuclease RNase MRP is a complex of RNA molecule and several proteins and it participates on cleavage of mitochondrial primers responsible for DNA replication and on pre-rRNA processing in the nucleolus. The locus of the gene has been mapped to the short arm of chromosome 9.
Patients with CHH usually suffer from cellular immunodeficiency. In the study of 108 Finnish patients with CHH there was detected mild to moderate form of lymphopenia, decreased delayed type of hypersensitivity and impaired responses to phytohaemagglutinin. This leads to susceptibility to and, in some more severe cases, mortality from infections early in childhood. There has also been detected combined immunodeficiency in some patients  Patients with CHH often have increased predispositions to malignancies.
- James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. ISBN 0-7216-2921-0.
- McKusick VA, Eldridge R, Hosteler JA, Ruangwit U, Egeland JA; Eldridge; Hostetler; Ruangwit; Egeland (1965). "Dwarfism In The Amish. II. Cartilage-hair hypoplasia". Bull Johns Hopkins Hosp 116: 285–326. PMID 14284412.
- Chavez, Paul (2000-12-24). "The name of my condition is Cartilage Hair Syndrome Hypoplasia, but you can just call me Billy". ABC News. Retrieved 2010-01-26.
- Sulisalo T, Makitie O, Sistonen P, Ridanpaa M, el Rifai W, Ruuskanen O, de la Chapelle A, Kaitila L; Mäkitie; Sistonen; Ridanpää; El-Rifai; Ruuskanen; de la Chapelle; Kaitila (1997). "Uniparental disomy in cartilage-hair hypoplasia". European Journal of Human Genetics 5 (1): 35–42. PMID 9156319.
- Bonafé L, Schmitt K, Eich G, Giedion A, Superti-Furga A; Schmitt; Eich; Giedion; Superti-Furga (February 2002). "RMRP gene sequence analysis confirms a cartilage-hair hypoplasia variant with only skeletal manifestations and reveals a high density of single-nucleotide polymorphisms". Clin. Genet. 61 (2): 146–51. doi:10.1034/j.1399-0004.2002.610210.x. PMID 11940090.
- Ridanpää M, van Eenennaam H, Pelin K, Chadwick R, Johnson C, Yuan B, vanVenrooij W, Pruijn G, Salmela R, Rockas S, Mäkitie O, Kaitila I, de la Chapelle A; Van Eenennaam; Pelin; Chadwick; Johnson; Yuan; Vanvenrooij; Pruijn; Salmela; Rockas; Mäkitie; Kaitila; de la Chapelle (2001). "Mutations in the RNA component of RNase MRP cause a pleiotropic human disease, cartilage-hair hypoplasia". Cell 104 (2): 195–203. doi:10.1016/S0092-8674(01)00205-7. PMID 11207361.
- Martin AN, Li Y; Li (2007). "RNase MRP RNA and human genetic diseases". Cell Res 17 (3): 219–26. doi:10.1038/sj.cr.7310120. PMID 17189938.
- Kavadas FD, Giliani S, Gu Y, Mazzolari E, Bates A, Pegoiani E, Roifman CM, Notarangelo LD; Giliani; Gu; Mazzolari; Bates; Pegoiani; Roifman; Notarangelo (2008). "Variability of clinical and laboratory features among patients with ribonuclease mitochondrial RNA processing endoribonuclease gene mutations". The Journal of Allergy and Clinical Immunology 122 (6): 1178–84. doi:10.1016/j.jaci.2008.07.036. PMID 18804272.
- Hsieh, C. L.; Donlon, T. A.; Darras, B. T.; Chang, D. D.; Topper, J. N.; Clayton, D. A.; Francke, U (1990). "The gene for the RNA component of the mitochondrial RNA-processing endoribonuclease is located on human chromosome 9p and on mouse chromosome 4". Genomics 6 (3): 540–544. doi:10.1016/0888-7543(90)90483-b. PMID 2328993.
- Topper, J. N.; Clayton, D. A. (1990). "Characterization of human MRP/Th RNA and its nuclear gene: Full length MRP/Th RNA is an active endoribonuclease when assembled as an RNP". Nucleic Acids Research 18 (4): 793–799. doi:10.1093/nar/18.4.793. PMC 330329. PMID 1690392.
- Sulisalo, T; Sistonen, P; Hästbacka, J; Wadelius, C; Mäkitie, O; de la Chapelle, A; Kaitila, I (1993). "Cartilage-hair hypoplasia gene assigned to chromosome 9 by linkage analysis". Nature Genetics 3 (4): 338–341. doi:10.1038/ng0493-338. PMID 7981754.
- Mäkitie, O; Kaitila, I (1993). "Cartilage-hair hypoplasia--clinical manifestations in 108 Finnish patients". European journal of pediatrics 152 (3): 211–7. doi:10.1007/bf01956147. PMID 8444246.
- Saulsbury, F. T.; Winkelstein, J. A.; Davis, L. E.; Hsu, S. H.; d'Souza, B. J.; Gutcher, G. R.; Butler, I. J. (1975). "Combined immunodeficiency and vaccine-related poliomyelitis in a child with cartilage-hair hypoplasia". The Journal of pediatrics 86 (6): 868–72. doi:10.1016/s0022-3476(75)80216-2. PMID 165279.