Quantitative copy number analysis by Multiplex Ligation-dependent Probe Amplification (MLPA) of BRCA1-associated breast cancer regions identifies BRCAness.

INTRODUCTION: Our group has previously employed array Comparative Genomic Hybridization (aCGH) to assess the genomic patterns of BRCA1-mutated breast cancers. We have shown that the so-called BRCA1-like(aCGH) profile is also present in about half of all triple-negative sporadic breast cancers and is predictive for benefit from intensified alkylating chemotherapy. As aCGH is a rather complex method, we translated the BRCA1(aCGH) profile to a Multiplex Ligation-dependent Probe Amplification (MLPA) assay, to identify both BRCA1-mutated breast cancers and sporadic cases with a BRCA1-like(aCGH) profile. METHODS: The most important genomic regions of the original aCGH based classifier (3q22-27, 5q12-14, 6p23-22, 12p13, 12q21-23, 13q31-34) were mapped to a set of 34 MLPA probes. The training set consisted of 39 BRCA1-like(aCGH) breast cancers and 45 non-BRCA1-like(aCGH) breast cancers, which had previously been analyzed by aCGH. The BRCA1-like(aCGH) group consisted of germline BRCA1-mutated cases and sporadic tumours with low BRCA1 gene expression and/or BRCA1 promoter methylation. We trained a shrunken centroids classifier on the training set and validation was performed on an independent test set of 40 BRCA1-like(aCGH) breast cancers and 32 non-BRCA1-like(aCGH) breast cancer tumours. In addition, we validated the set prospectively on 69 new triple-negative tumours. RESULTS: BRCAness in the training set of 84 tumours could accurately be predicted by prediction analysis of microarrays (PAM) (accuracy 94%). Application of this classifier on the independent validation set correctly predicted BRCA-like status of 62 out of 72 breast tumours (86%). Sensitivity and specificity were 85% and 87%, respectively. When the MLPA-test was subsequently applied to 46 breast tumour samples from a randomized clinical trial, the same survival benefit for BRCA1-like tumours associated with intensified alkylating chemotherapy was shown as was previously reported using the aCGH assay. CONCLUSIONS: Since the MLPA assay can identify BRCA1-deficient breast cancer patients, this method could be applied both for clinical genetic testing and as a predictor of treatment benefit. BRCA1-like tumours are highly sensitive to chemotherapy with DNA damaging agents, and most likely to poly ADP ribose polymerase (PARP)-inhibitors. The MLPA assay is rapid and robust, can easily be multiplexed, and works well with DNA derived from paraffin-embedded tissues.

Methylation-Specific Multiplex Ligation-Dependent Probe Amplification (MS-MLPA).

This chapter describes a method for the rapid assessment of promoter hypermethylation levels or methylation of imprinted regions in human genomic DNA extracted from various sources using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA). Multiplex ligation-dependent probe amplification (MLPA) is a powerful and easy-to-perform PCR-based technique that can identify gains, amplifications, losses, deletions, methylation and mutations of up to 55 targets in a single reaction, while requiring only minute quantities of DNA (about 50 ng) extracted from blood, fresh frozen or formalin-fixed paraffin-embedded materials. Methylation-specific MLPA (MS-MLPA) is a variant of MLPA, which does not require sodium bisulfite conversion of unmethylated cytosine residues, but instead makes use of the methylation-sensitive endonuclease HhaI. MS-MLPA probes are designed to contain a HhaI recognition site (GCGC) and thus target one CpG dinucleotide within a CpG island. If the HhaI recognition site is not methylated, HhaI will cut the probe-sample DNA hybrid and no PCR product will be formed. If the target DNA is methylated, HhaI is not able to cut, and the fragment will be amplified during subsequent PCR. For data analysis, MS-MLPA peak patterns of the HhaI-treated and -untreated reactions are compared, leading to calculation of a methylation percentage. The methylation profile of a test sample is assessed by comparing the probe methylation percentages obtained on the test sample to the percentages of the reference samples. MS-MLPA can be combined with copy number and point mutation detection in the same reaction.

Optimal Fixation Conditions and DNA Extraction Methods for MLPA Analysis on FFPE Tissue-Derived DNA.

OBJECTIVES: Molecular genetic analysis of formalin-fixed, paraffin-embedded (FFPE) tissues is of great importance both for research and diagnostics. Multiplex ligation-dependent probe amplification (MLPA) is a widely used technique for gene copy number determination, and it has been successfully used for FFPE tissue-extracted DNA analysis. However, there have been no studies addressing the effect of tissue fixation procedures and DNA extraction methods on MLPA. This study therefore focuses on selecting optimal preanalytic conditions such as FFPE tissue preparation conditions and DNA extraction methods. METHODS: Healthy tissues were fixed in buffered or nonbuffered formalin for 1 hour, 12 to 24 hours, or 48 to 60 hours at 4 °C or at room temperature. DNA extracted from differently fixed and subsequently paraffin-embedded tissues was used for MLPA. Four commercial DNA extraction kits and one in-house method were compared. RESULTS: Tissues fixed for 12 to 24 hours in buffered formalin at room temperature produced DNA with the most optimal quality for MLPA. The in-house FFPE DNA extraction method was shown to perform as efficient as or even superior to other methods in terms of suitability for MLPA, time and cost-efficiency, and ease of performance. CONCLUSIONS: FFPE-extracted DNA is well suitable for MLPA analysis, given that optimal tissue fixation and DNA extraction methods are chosen.