Targeted Next-Generation Sequencing Identifies a Recurrent Mutation in <i>MCPH1</i> Associating with Hereditary Breast Cancer Susceptibility

<div><p>Breast cancer is strongly influenced by hereditary risk factors, a majority of which still remain unknown. Here, we performed a targeted next-generation sequencing of 796 genes implicated in DNA repair in 189 Finnish breast cancer cases with indication of hereditary disease susceptibility and focused the analysis on protein truncating mutations. A recurrent heterozygous mutation (c.904_916del, p.Arg304ValfsTer3) was identified in early DNA damage response gene, <i>MCPH1</i>, significantly associating with breast cancer susceptibility both in familial (5/145, 3.4%, <i>P</i> = 0.003, OR 8.3) and unselected cases (16/1150, 1.4%, <i>P</i> = 0.016, OR 3.3). A total of 21 mutation positive families were identified, of which one-third exhibited also brain tumors and/or sarcomas (<i>P</i> = 0.0007). Mutation carriers exhibited significant increase in genomic instability assessed by cytogenetic analysis for spontaneous chromosomal rearrangements in peripheral blood lymphocytes (<i>P</i> = 0.0007), suggesting an effect for MCPH1 haploinsufficiency on cancer susceptibility. Furthermore, 40% of the mutation carrier tumors exhibited loss of the wild-type allele. These findings collectively provide strong evidence for <i>MCHP1</i> being a novel breast cancer susceptibility gene, which warrants further investigations in other populations.</p></div

Examples of <i>MCPH1</i> mutation positive families (A-C).

<p>Patients with breast cancer are marked with black half circles. Other cancer types are marked with grey squares. The age at diagnosis, when known, is marked below the cancer type. Individuals genotyped for <i>MCPH1</i> c.904_916del are marked with either a plus (mutation positive) or a minus sign (mutation negative). A slashed pedigree symbol indicates a deceased individual. Triangle indicates the initially studied index patient (BR-0653, BR-0887 and BR-0154, respectively). Abbreviations: Bas: basalioma, Bt: brain tumor, Br: breast cancer, Col: colon cancer, Csu: cancer site unknown, Lar: laryngeal cancer, Ov: ovarian tumor, Pro: prostate cancer, Ut: uterine cancer, Vul: vulvar cancer.</p

Effect of <i>MCPH1</i> c.904_916del mutation at the mRNA and protein level.

<p>(<b>A</b>) Schematic presentation of the MCPH1 protein and the position of the observed truncating mutation. (<b>B</b>) Sequence chromatogram comparisons of genomic DNA and cDNA of heterozygous mutation carriers and a wild-type control. (<b>C</b>) Immunoblotting of 3 mutation carriers and 3 non-carriers with an antibody directed towards the amino-terminus of MCPH1. The representative image of altogether three independent experiments is shown.</p

Occurrence of chromosomal aberrations in blood lymphocyte metaphases of heterozygous <i>MCPH1</i> c.904_916del mutation carriers and healthy controls.

<p>Occurrence of chromosomal aberrations in blood lymphocyte metaphases of heterozygous <i>MCPH1</i> c.904_916del mutation carriers and healthy controls.</p

Family history of cancers of <i>MCPH1</i> c.904_916del positive index cases^a.

<p>Family history of cancers of <i>MCPH1</i> c.904_916del positive index cases<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005816#t002fn004" target="_blank">^a</a>.</p

SNPs associated with ILC (P<5×10⁻⁸) or LCIS (P<0.05) in a pooled lobular analysis (GLACIER and BCAC).

<p>SNPs associated with ILC (P<5×10⁻⁸) or LCIS (P<0.05) in a pooled lobular analysis (GLACIER and BCAC).</p

rs11977670, chromosome 7:139942304 G>A, and association ILC in populations of European ancestry.

<p>rs11977670, chromosome 7:139942304 G>A, and association ILC in populations of European ancestry.</p

Forest plot for rs11977670.

<p>Forest plot for rs11977670.</p

SNPs showing differential lobular and ductal associations with breast cancer risk in BCAC subjects (ER+ tumours only).

<p>SNPs showing differential lobular and ductal associations with breast cancer risk in BCAC subjects (ER+ tumours only).</p

Association with risk of breast cancer for rs11977670 stratified by breast cancer tumour subtypes (Pooled analysis, BCAC, GLACIER, UK PHASE II).

<p>Association with risk of breast cancer for rs11977670 stratified by breast cancer tumour subtypes (Pooled analysis, BCAC, GLACIER, UK PHASE II).</p