Identification of an AluY‐mediated deletion of exon 5 in the CPOX gene by MLPA analysis in patients with hereditary coproporphyria

Abstract

Hereditary coproporphyria (HCP) is an autosomal dominantly inherited hepatic porphyria, caused by a mutation in the coproporphyrinogen oxidase (CPOX) gene. The genetic defect leads to a partial defect of CPOX, the sixth enzyme involved in haem biosynthesis. Affected individuals can develop acute life-threatening attacks of neurovisceral symptoms and/or more rarely cutaneous symptoms such as skin fragility and blistering. The identification of the genetic defect in HCP families is of crucial importance to detect the carrier status which allows counselling to prevent possible triggering factors, e.g. certain drugs, alcohol, or fasting. In a total of nine Swedish HCP families, routine gene sequence analysis had identified a causative mutation in only five. In the present study, using an in-house developed synthetic probe set for multiplex ligation-dependent probe amplification (MLPA) analysis, we detected a deletion of the fifth exon in the CPOX gene in the remaining four families. The deletion is 3381 bp in size and has originated by an Alu-mediated mechanism. This finding emphasizes the usefulness of MLPA analysis as a complement to gene sequencing for comprehensive genetic diagnostics in HCP patients.

Partial protoporphyrinogen oxidase (PPOX) gene deletions, due to different Alu-mediated mechanisms, identified by MLPA analysis in patients with variegate porphyria

“…Gene dosage analysis has earlier been shown to increase the diagnostic sensitivity for the two other acute porphyrias (AIP and HCP) [28] and large deletions have been reported for the HMBS and CPOX genes, respectively [28-30]. We describe here two partial deletions within the PPOX gene, indicating that partial gene deletions should be considered in the genetic diagnosis of all acute porphyrias.…”

Role of genetic testing in the management of patients with inherited porphyria and their families

“…Direct sequencing of all the regions of interest is now often the preferred option. Because a number of large deletions encompassing one or more exons have been identified in the porphyrias, 40–42,107–109 gene dosage analysis by quantitative fluorescent PCR 110 or multiple ligation dependent analysis 40 should always be carried out if a mutation is not detected by sequencing of genomic DNA. Single exon deletions must always be confirmed as variants under primers or probes can mimic these.…”

“…Mutations are distributed throughout the genes; most are point mutations but a few large deletions have been detected in the HMBS and CPOX genes. 40–42 Mutations decrease enzyme activities in all tissues with the important exception of about 3% of AIP families (variant AIP) which have HMBS mutations that alter the N-terminus of the ubiquitous isoform and therefore do not impair activity in erythroid cells. 43,44…”

Detection of exon skipping events in BRCA1 RNA using MLPA kit P002

“…The normalization of the data was performed using a spreadsheet according to the Manual spreadsheet-based MLPA analysis instructions (available on the MRC-Holland website: www.MLPA.com ). The threshold values for deletions and duplications were set to 0.75–1.25, respectively, which are also used for DNA analysis [ 13 – 16 ].…”