The molecular basis of classic Ehlers-Danlos syndrome: A comprehensive study of biochemical and molecular findings in 48 unrelated patients

Abstract

Classic Ehlers-Danlos syndrome (EDS) is characterized by fragile and hyperextensible skin, atrophic scarring, and joint hypermobility. Mutations in the COL5A1 and the COL5A2 gene encoding the alpha1(V) and the alpha2(V) chains, respectively, of type V collagen have been shown to cause the disorder, but it is unknown what proportion of classic EDS patients carries a mutation in these genes. We studied fibroblast cultures from 48 patients with classic EDS by SDS-PAGE for the presence of type V collagen defects. An abnormal collagen pattern was detected in only 2 out of 48 cell lines, making this a poor method for routine diagnostic evaluation. A total of 42 out of 48 (88%) patients were heterozygous for an expressed polymorphic variant in COL5A1. cDNA from 18 (43%) of them expressed only one COL5A1 allele. In 37 patients, the COL5A1/A2 genes were then analyzed by SSCP and conformation sensitive gel electrophoresis (CSGE). A total of 26 patients that were mutation-negative after SSCP/CSGE screening were reanalyzed by dHPLC. In addition, 11 other patients were analyzed by dHPLC only. In total, 17 mutations leading to a premature stop codon and five structural mutations were identified in the COL5A1 and the COL5A2 genes. In three patients with a positive COL5A1 null-allele test, no causal mutation was found. Overall, in 25 out of 48 patients (52%) with classic EDS, an abnormality in type V collagen was confirmed. Variability in severity of the phenotype was observed, but no significant genotype-phenotype correlations emerged. The relatively low mutation detection rate suggests that other genes are involved in classic EDS. We excluded the COL1A1, COL1A2, and DCN gene as major candidate genes for classic EDS, since no causal mutation in these genes was found in a number of patients who tested negative for COL5A1 and COL5A2.

Clinical and genetic aspects of Ehlers-Danlos syndrome, classic type

“…Abnormal proteins will migrate differently on the gel, when compared with control samples. 49 However, because type V collagen is synthesized by fibroblasts at low levels, alterations in electrophoretic mobility are poorly reproducible, making this an ineffective method for routine diagnostic evaluation. The test, however, helps to exclude other subtypes of EDS, such as the vascular, kyphoscoliotic, arthrochalasis, and the dermatosparaxis type in individuals in which clinical differential diagnosis is difficult.…”

“…COL5A1 null alleles are detected in approximately 30 -40% of individuals with classic EDS. 49 Sequence analysis by Sanger sequencing of the COL5A1 and the COL5A2 gene can be performed either on gDNA or cDNA. Once the mutation is known, its presence or absence can easily be verified on gDNA obtained from leukocytes from the patient and from relatives.…”

“…In approximately one third of individuals with classic EDS, nonsense or frameshift mutations are responsible for a nonfunctional COL5A1 allele. 49,[53][54][55] Nonsense, frameshift, or splice site mutations that introduce a premature termination codon are usually responsible for this nonfunctional COL5A1 allele. A variety of mechanisms lead to nonsense-mediated decay of the mutation-bearing mRNA.…”

“…These structural mutations are most commonly splice site mutations that result in exon skipping and a few point mutations that result in the substitution for glycine in the triple-helical region of the collagen molecule. 49,[55][56][57][58][59][60][61] In contrast to other disorders characterized by mutations in the fibrillar collagen genes, remarkably few mutations have been found that result from the substitution of a glycine by a bulkier amino acid.…”

Syndrome d’Ehlers-Danlos : à propos d’un cas

“…Le SED forme donc une famille hétérogène regroupant plusieurs maladies génétiques du tissu conjonctif, ayant en commun la triade clinique suivante [2][3][4] Le SED est surtout lié à l'apparition d'un codon de terminaison précoce dans le gêne codant pour le collagène de type V, mais il peut aussi être secondaire à des anomalies des enzymes impliquées dans la biosynthèse du collagène [5,6]. D'autres molécules de la matrice extra-cellulaire, telle que la ténascine X, pourraient être responsables de l'apparition de cette affection [7].…”