Lamin A/C mutation analysis in a cohort of 324 unrelated patients with idiopathic or familial dilated cardiomyopathy

Abstract

Background: Lamin A/C mutations are a well-established cause of dilated cardiomyopathy (DCM), although their frequency has not been examined in a large cohort of patients. We sought to examine the frequency of mutations in LMNA, the gene encoding lamin A/C, in patients with idiopathic (IDC) or familial dilated cardiomyopathy (FDC).

Methods: Clinical cardiovascular data, family histories, and blood samples were collected from 324 unrelated IDC probands, of whom 187 had FDC. DNA samples were sequenced for nucleotide alterations in LMNA. Likely protein-altering mutations were followed up by evaluating additional family members, when possible.

Results: We identified 18 protein-altering LMNA variants in 19 probands or 5.9% of all cases (7.5% of FDC; 3.6% of IDC). Of the 18 alterations, 11 were missense (one present in 2 kindreds), 3 were nonsense, 3 were insertion/deletions, and 1 was a splice site alteration. Conduction system disease and DCM were common in carriers of LMNA variants. Unexpectedly, in 6 of the 19 kindreds with a protein-altering LMNA variant (32%), at least one affected family member was negative for the LMNA variant.

Conclusions: Lamin A/C variants were observed with a frequency of 5.9% in probands with DCM. The novel observation of FDC pedigrees in which not all affected individuals carry the putative disease-causing LMNA mutation suggests that some protein-altering LMNA variants are not causative or that some proportion of FDC may be because of multiple causative factors. These findings warrant increased caution in FDC research and molecular diagnostics.

Figure 1. Mutations in LMNA and the lamin A and C proteins and amino acid conservation

Panel A. The LMNA gene is shown. Lamin A (shown below) is coded by exons 1−12 and is a total of 664 amino acids in length. Lamin C (above) is coded by exons 1−9 and an alternatively spliced exon 10, and is 572 amino acids long. The locations of the 18 mutations are labeled with their respective letters. Panel B. Sequencing electropherograms show heterozygosity for each mutation labeled A through S. The nucleotide changes and their effects on amino acid sequence are indicated. Abbreviations are as follows: X, stop; fs, frame shift; del, deletion; ins, insertion. All amino acids changed by mutations were conserved across mouse, rat, chicken, and zebrafish except for mutation D/E and R (mouse, rat and chicken) and mutation O (mouse, rat).Panel C. SIFT or polyphen data are shown for missense mutations. Panel D. Sequence data shows skipping of LMNA exon 2 for Mutation C. The 357−1G>T splice site mutation results in a minor PCR product representing a transcript in which exon 3 follows immediately after exon 1.

Figure 2. Pedigrees A, C, D, E, F, H, K, M, Q, R

Pedigrees have been labeled by letter, which correspond to their respective mutation as shown in Figure 1. Squares represent males, circles females. An arrowhead denotes the proband. A diagonal line marks deceased individuals. Solid symbols indicate idiopathic dilated cardiomyopathy with or without heart failure, shaded symbols represent any cardiovascular abnormality. Open symbols represent unaffected individuals. The presence or absence of the familial LMNA mutation is indicated by a + or − symbol, respectively. Obligate carriers are noted in parenthesis, (+). Available clinical data are provided under the symbols. The first line is the current age or age of death, followed by the age of onset in parenthesis, and the current major medical diagnosis if alive, or the cause of death if known. Age at cardiac transplantation, when applicable, is the second line. The next line describes LV size and function; Z score is the standard deviation from the mean of the left ventricular end-diastolic dimension measured by echocardiography. The ejection fraction follows; where values are not available, descriptive terms are provided. The last line describes arrhythmias and/or conduction system disease. Abbreviations are as follows: Afib, atrial fibrillation; Asym, asymptomatic; Arr, arrhythmia; ASHD, atherosclerotic heart disease; AV, atrioventricular; AVB atrioventricular block; 1AVB, 2AVB, first or second degree AVB, respectively; A/W, alive and well; bigem, bigeminy; Bi-F, bi-fascicular block; BiV-ICD; biventricular pacemaker with implantable cardiac defibrillator; Br, bradycardia; CHD, congenital heart disease; CM, cardiomyopathy, unknown type; CVA, cerebrovascular accident; CVD, cardiovascular disease; EF, ejection fraction; enl hrt, enlarged heart; Htn, hypertension; HtTr, heart transplant; ICD, implantable cardiac defibrillator; IRBBB, incomplete right bundle branch block; irreg, irregular; HB, heart beat; LBBB, left bundle branch block; Nl scr, normal cardiovascular screening; NSR, normal sinus rhythm; NSSTT, non-specific ST T changes on ECG; NSVT, nonsustained ventricular tachycardia; PM, pacemaker; occ, occasional; PAC, paroxysmal atrial contractions; PVCs, premature ventricular contractions; RBBB, right bundle branch block; SCD, sudden cardiac death; tachy, sinus tachycardia; SSS, sick sinus syndrome; VT, ventricular tachycardia; Z, z-score.

Figure 3. Pedigrees with incomplete segregation

Refer to Figure 2 legend.