Two mutations in Marfan syndrome resulting in truncated fibrillin polypeptides.

Abstract

Biochemical and molecular genetic studies have recently suggested that mutations in the gene coding for fibrillin on chromosome 15 result in Marfan syndrome. To our knowledge, only one mutation in the fibrillin gene has been published. Here we report the results of screening 20 unrelated MES patients for mutations in fibrillin cDNA by the singlestrand conformation polymorphism technique. We found two mutations, both of which appear in the heterozygote form and code for a shortened fibrillin polypeptide. The first mutation is a large in-frame deletion of 366 bases of the fibrillin mRNA, shown to result in a truncated but secreted polypeptide found in the fibroblast culture of the patient. The second mutation is a G-to-A transition resulting in the substitution of a stop codon for a tryptophan codon and thus predicting the premature termination of the polypeptide chain. We screened 60 other, unrelated MFS patients for these mutations as well as for the previously reported mutation (arginine-239 to proline) and found none of the three mutations in any of these patients. These data suggest that most MFS families carry their own distinct mutation.The Marfan syndrome (MFS) is an autosomal dominant connective-tissue disorder characterized by cardiovascular, ocular, and skeletal manifestations (1). By the random linkage approach, the MFS locus was assigned to the long arm of chromosome 15 in three Finnish families (2). Later, the linkage was confirmed in families from diverse ethnic backgrounds, and the locus was more precisely localized to the immediate vicinity of the polymorphic marker DISSI (3-5). To date, linkage analyses of chromosome 15 markers in families from different populations have not revealed any evidence for genetic heterogeneity underlying MFS (3-5).Independent simultaneous immunohistochemical analyses demonstrated a nearly constant deficiency of fibrillin, an extracellular protein (6), in skin sections and cultured fibroblasts from MFS patients (7). Subsequently, the fibrillin cDNA was cloned (8) and the corresponding locus was mapped by in situ hybridization to chromosome 15q21.1 (9, 10), in the vicinity of the marker DJSSI. The MATERIALS AND METHODSPatients. The material consisted of fibroblast lines established from skin biopsies of 20 unrelated MFS patients from Finland and the United Kingdom and blood samples of these and 41 additional MFS patients from Belgium, Finland, the Netherlands, Switzerland, the United Kingdom, and the United States, including patients both with and without family history of MFS. All the samples were taken in accordance with the Helsinki Declaration. The diagnoses were made by using the criteria established by Beighton et al. (12).The patient R.H. was a 48-year-old man with cardiovascular, eye, and skeletal symptoms and signs of MFS. He was a member of a three-generation English pedigree none of whom have ectopia lentis. The propositus' mother had peripheral retinal degeneration and retinal detachment. A brother and sister of the propositus had severe mitral va...

An accurate method for comparing transcript levels of two alleles or highly homologous genes: application to fibrillin transcripts in Marfan patients' fibroblasts.

“…All patient samples were collected in accordance with the Helsinki Declaration. Fibroblasts from the MFS patients and control individuals were cultured as described previously (Kainulainen et al 1992). The passage number of the cells varied between 2 and 11.…”

Elucidation of the gene defect in Marfan syndrome Success by two complementary research strategies

“…We found a 366 bp deletion of fibrillin mRNA predicting a polypeptide chain 122 amino acids shorter than normal in a 4%year-old British male [30]. This mutation was shown to cosegregate with the disease in his family in which Marfan syridrome had been diagnosed in three generations.…”

“…The R239P mutation occurred in a conserved amino acid within such a six-cysteine motif suggesting that the mutation occurred at a functionally significant site of the polypeptide chain. 30]. TWO types of repelhive molifs have been idcntilied in the dbrillin sequence, a G-cysteine motif homologous to that found in the EGF-precursor ~noleculc and PII tl-cyskinc motif homologous to a motif seen in TGF#I molecules [29].…”

“…The third detected mutation was a heterozygotic Gto-A transition at nucleoride 5574 found in the cDNA of a %-year-old sporadic Finnish Marfan patient [30]. The consequence of this mutation was the substitution of a stop codon for Trp"5n (WlS58) predicting the termination of the flbrillin polypeptide chain 116 amino acids too early.…”

Marfan syndrome in the third Millennium

“…No major rearrangements have been identified except for three cases of multi-exon deletions. 35,36 Three categories of mutations have been described: (1) missense mutations, (2) small insertions or deletions, mutations causing premature termination of translation and (3) exon-skipping mutations.…”