RESUMEN
Ehlers-Danlos syndrome type VI (EDSVI) is an autosomal recessively inherited connective tissue disease, characterized by kyphoscoliosis, muscular hypotonia and ocular manifestations. The cause of the syndrome is a deficiency in the activity of lysyl hydroxylase (LH), one of the enzymes involved in the post-translational modification of collagens. We describe here an unusual compound heterozygote British patient with EDSVI. Our investigations indicate that a maternally inherited nonsense mutation (Y511X) in exon 14 of the LH gene (PLOD1) results in a reduction of the mRNA level as well as a skipping of exon 14 sequences in the mRNA that produces a protein shortened by 38 amino acids. The transcription of the other allele of the LH gene is considerably reduced from the normal for reasons that are not yet known. As a consequence, the LH activity of the skin fibroblasts of the patient is markedly reduced.
Asunto(s)
Codón sin Sentido/genética , Síndrome de Ehlers-Danlos/genética , Procolágeno-Lisina 2-Oxoglutarato 5-Dioxigenasa/genética , Empalme del ARN/genética , ARN Mensajero/metabolismo , Southern Blotting , Desoxirribonucleasas de Localización Especificada Tipo II/metabolismo , Fibroblastos , Humanos , Mutación , Reacción en Cadena de la Polimerasa , Reino UnidoRESUMEN
A British patient with EDS VI had two novel null mutations in the lysyl hydroxylase gene, one nucleotide deletion in the acceptor splice site of intron 4 in one allele, and an insertion of a C nucleotide in exon 2 of the other allele. The abnormal alleles lead to a markedly decreased lysyl hydroxylase mRNA levels, the finding making the affected cells different from the normal cells. In addition to the mutation analysis, we have revealed many exon-deleted splicing variants for lysyl hydroxylase mRNA which were first discovered in the affected cells, but tracks of similarly spliced mRNA species are also found in the cytoplasm of normal human skin fibroblasts. The data suggest that the splicing machinery of the cell is leaky generating differently spliced transcripts in the cell but only in a small amounts.
Asunto(s)
Síndrome de Ehlers-Danlos/enzimología , Procolágeno-Lisina 2-Oxoglutarato 5-Dioxigenasa/genética , Empalme Alternativo , Células Cultivadas , Femenino , Fibroblastos/química , Heterocigoto , Humanos , Masculino , Mutación , Reacción en Cadena de la Polimerasa , Procolágeno-Lisina 2-Oxoglutarato 5-Dioxigenasa/metabolismo , Procolágeno-Prolina Dioxigenasa/metabolismo , ARN Mensajero/metabolismoRESUMEN
We report the first deletion mutation and the first splicing defect in the lysyl hydroxylase gene in a compound heterozygote patient with Ehlers-Danlos syndrome type VI with markedly reduced lysyl hydroxylase activity. Northern analysis of the RNA isolated from skin fibroblasts of the patient demonstrated the presence of a truncated lysyl hydroxylase mRNA. PCR and sequence analysis confirmed the truncation and indicated that the cells contain two types of shortened mRNAs, one lacking the sequences corresponding to exon 16 and the other lacking that corresponding to exon 17 of the lysyl hydroxylase gene. Analysis of genomic DNA revealed deletion of the penultimate adenosine from the 3' end of intron 15 from one allele. This defect was probably responsible for the skipping of exon 16 sequences from the transcript. The other allele, inherited from the mother, contains an Alu-Alu recombination with a deletion of about 3,000 nucleotides from the gene; this abnormality explains the lack of exon 17 sequences. The identified mutations in exon 16 and exon 17 do not alter the reading frame of the transcripts.
Asunto(s)
Alelos , Empalme Alternativo , Síndrome de Ehlers-Danlos/enzimología , Síndrome de Ehlers-Danlos/genética , Eliminación de Gen , Heterocigoto , Procolágeno-Lisina 2-Oxoglutarato 5-Dioxigenasa/genética , Células Cultivadas , Fibroblastos , Humanos , Procolágeno-Lisina 2-Oxoglutarato 5-Dioxigenasa/deficiencia , ARN Mensajero/análisis , Secuencias Repetitivas de Ácidos Nucleicos , PielRESUMEN
The type VI variant of the Ehlers-Danlos syndrome (EDS) is a recessively inherited connective-tissue disorder. The characteristic features of the variant are muscular hypotonia, kyphoscoliosis, ocular manifestations, joint hypermobility, skin fragility and hyperextensibility, and other signs of connective-tissue involvement. The biochemical defect in most but not all patients is a deficiency in lysyl hydroxylase activity. Lysyl hydroxylase is an enzyme that catalyzes the formation of hydroxylysine in collagens and other proteins with collagen-like amino acid sequences. We have recently reported an apparently homozygous large-duplication rearrangement in the gene for lysyl hydroxylase, leading to the type VI variant of EDS in two siblings. We now report an identical, apparently homozygous large duplication in an unrelated 49-year-old female originally analyzed by Sussman et al. Our simple-sequence-repeat-polymorphism analysis does not support uniparental isodisomy inheritance for either of the two duplications. Furthermore, we indicate in this study that the duplication in the lysyl hydroxylase gene is caused by an Alu-Alu recombination in both families. Cloning of the junction fragment of the duplication has allowed synthesis of appropriate primers for rapid screening for this rearrangement in other families with the type VI variant of EDS.