title: Evolutionary comparison provides evidence for pathogenicity of RMRP mutations.
abstract: Cartilage-hair hypoplasia (CHH) is a pleiotropic disease caused by recessive mutations in the RMRP gene that result in a wide spectrum of manifestations including short stature, sparse hair, metaphyseal dysplasia, anemia, immune deficiency, and increased incidence of cancer. Molecular diagnosis of CHH has implications for management, prognosis, follow-up, and genetic counseling of affected patients and their families. We report 20 novel mutations in 36 patients with CHH and describe the associated phenotypic spectrum. Given the high mutational heterogeneity (62 mutations reported to date), the high frequency of variations in the region (eight single nucleotide polymorphisms in and around RMRP), and the fact that RMRP is not translated into protein, prediction of mutation pathogenicity is difficult. We addressed this issue by a comparative genomic approach and aligned the genomic sequences of RMRP gene in the entire class of mammals. We found that putative pathogenic mutations are located in highly conserved nucleotides, whereas polymorphisms are located in non-conserved positions. We conclude that the abundance of variations in this small gene is remarkable and at odds with its high conservation through species; it is unclear whether these variations are caused by a high local mutation rate, a failure of repair mechanisms, or a relaxed selective pressure. The marked diversity of mutations in RMRP and the low homozygosity rate in our patient population indicate that CHH is more common than previously estimated, but may go unrecognized because of its variable clinical presentation. Thus, RMRP molecular testing may be indicated in individuals with isolated metaphyseal dysplasia, anemia, or immune dysregulation.
authors.affiliation: Division of Molecular Pediatrics, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. Luisa.Bonafe@chuv.ch
authors.forename: Luisa
authors.initials: L
authors.lastname: Bonafé
authors.forename: Emmanouil T
authors.initials: ET
authors.lastname: Dermitzakis
authors.forename: Sheila
authors.initials: S
authors.lastname: Unger
authors.forename: Cheryl R
authors.initials: CR
authors.lastname: Greenberg
authors.forename: Belinda A
authors.initials: BA
authors.lastname: Campos-Xavier
authors.forename: Andreas
authors.initials: A
authors.lastname: Zankl
authors.forename: Catherine
authors.initials: C
authors.lastname: Ucla
authors.forename: Stylianos E
authors.initials: SE
authors.lastname: Antonarakis
authors.forename: Andrea
authors.initials: A
authors.lastname: Superti-Furga
authors.forename: Alexandre
authors.initials: A
authors.lastname: Reymond
mesh_terms: D000818:Animals; D001483:Base Sequence; D004722:Endoribonucleases / Q000235:genetics*; D019143:Evolution, Molecular; D005192:Family Health; D016678:Genome; D023281:Genomics; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010009:Osteochondrodysplasias / Q000235:genetics; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D012313:RNA / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D012313:RNA; D004722:Endoribonucleases; C058330:mitochondrial RNA-processing endoribonuclease