Mutations in the gene encoding capillary morphogenesis protein 2 cause juvenile hyaline fibromatosis and infantile systemic hyalinosis

Abstract

Juvenile hyaline fibromatosis (JHF) and infantile systemic hyalinosis (ISH) are autosomal recessive conditions characterized by multiple subcutaneous skin nodules, gingival hypertrophy, joint contractures, and hyaline deposition. We previously mapped the gene for JHF to chromosome 4q21. We now report the identification of 15 different mutations in the gene encoding capillary morphogenesis protein 2 (CMG2) in 17 families with JHF or ISH. CMG2 is a transmembrane protein that is induced during capillary morphogenesis and that binds laminin and collagen IV via a von Willebrand factor type A (vWA) domain. Of interest, CMG2 also functions as a cellular receptor for anthrax toxin. Preliminary genotype-phenotype analyses suggest that abrogation of binding by the vWA domain results in severe disease typical of ISH, whereas in-frame mutations affecting a novel, highly conserved cytoplasmic domain result in a milder phenotype. These data (1) demonstrate that JHF and ISH are allelic conditions and (2) implicate perturbation of basement-membrane matrix assembly as the cause of the characteristic perivascular hyaline deposition seen in these conditions.

Figure  1

Homozygosity mapping and genomic structure of CMG2. a, Homozygosity-mapping data from 18 microsatellite markers on chromosome 4q21 in consanguineous families with JHF and ISH, showing marker alleles, regions of homozygosity (boxed), and key recombination events in families H and P. The physical distances of the markers according to the November 2002 UCSC Human Genome Project Working Draft (see the UCSC Genome Bioinformatics Web site) are shown above each marker. b, Partial transcript map (drawn to scale) of the critical interval, showing currently known genes. c, Genomic structure of full-length CMG2.

Figure  2

Expression of CMG2. a, Sequence of full-length CMG2. b, RT-PCR of human cDNA multiple-tissue panel (Clontech), showing expression of ∼1.4 kb transcript in all tissues, except brain.

Figure  3

Sequence alignment of 50 amino acids in cytoplasmic domain of CMG2 and TEM8 in various species, showing high conservation. Black background indicates identical residues, and gray background indicates conservative substitutions. In pig, sheep, chicken, and zebrafish, the gene that the conserved region is from is currently unknown, because the full-length gene sequence is not available. The position of the missense mutation in family D is indicated by an arrow.

Figure  4

Genomic structure, protein domains, and mutation analysis of CMG2. a, Genomic structure and mutations in CMG2 with the exon sizes drawn to scale and the position of functional and conserved domains indicated (TM = transmembrane). The 5′ and 3′ UTRs are indicated by open boxes and are not drawn to scale. Introns are also not drawn to scale. The approximate positions of identified mutations are given, with identical mutations shown above each other. Green triangle = mutation resulting in premature truncation due to either small insertion/deletion/nonsense or splice-site alterations; red triangle = in-frame alterations due to either missense base substitutions or in-frame insertion/deletion; yellow triangle = splice-site mutations in which the precise pathogenic effect has not been identified. b, Pedigree structure and mutations in selected families with JHF and ISH, showing wild-type and mutant CMG2 sequence. The splice-site mutation in family C results in insertion of 4 bases and a frameshift.