EHLERS-DANLOS-SYNDROME TYPE-VI RESULTS FROM A NONSENSE MUTATION AND ASPLICE SITE-MEDIATED EXON-SKIPPING MUTATION IN THE LYSYL HYDROXYLASE GENE

We have characterized a patient with Ehlers Danlos syndrome type VI as a compound heterozygote for the lysyl hydroxylase (LH) gene, with a p athogenetic mutation in each allele contributing to the very low level s of mRNA and LH activity in his fibroblasts. Amplification of full-le ngth LH cDNAs resulted in normal-sized (2.9-kb) and shortened (2.8-kb) transcripts indicative of two populations of alleles. One allele cont ained a paternally inherited C-1557 to G transition that coded for a p remature stop codon (Y511X) and introduced an Nhe I restriction site i n exon 14 of the LH gene. The mutation in the other allele was an exon 5 deletion that produced the shortened polymerase chain reaction tran script and generated a premature stop codon at the beginning of exon 7 . Sequencing of genomic DNAs spanning exon 5 showed a mutation in the consensus donor splice site at the beginning of intron 5 (gt-->at) in both the proband and his mother. Via. reverse transcriptase-polymerase chain reaction, the parents' fibroblasts showed a disproportionately lower level of each mutant allele compared to their normal alleles. Th is study suggests that the decreased transcription of the LH gene, whi ch may be attributed to the presence of the nonsense mutations, accoun ts for the LH deficiency, and consequently, this patient's clinical ph enotype of Ehlers-Danlos syndrome type VI.