High proportion of genetic cases in patients with advanced cardiomyopathy including a novel homozygous Plakophilin 2-gene mutation

Abstract

Cardiomyopathies might lead to end-stage heart disease with the requirement of drastic treatments like bridging up to transplant or heart transplantation. A not precisely known proportion of these diseases are genetically determined. We genotyped 43 index-patients (30 DCM, 10 ARVC, 3 RCM) with advanced or end stage cardiomyopathy using a gene panel which covered 46 known cardiomyopathy disease genes. Fifty-three variants with possible impact on disease in 33 patients were identified. Of these 27 (51%) were classified as likely pathogenic or pathogenic in the MYH7, MYL2, MYL3, NEXN, TNNC1, TNNI3, DES, LMNA, PKP2, PLN, RBM20, TTN, and CRYAB genes. Fifty-six percent (n = 24) of index-patients carried a likely pathogenic or pathogenic mutation. Of these 75% (n = 18) were familial and 25% (n = 6) sporadic cases. However, severe cardiomyopathy seemed to be not characterized by a specific mutation profile. Remarkably, we identified a novel homozygous PKP2-missense variant in a large consanguineous family with sudden death in early childhood and several members with heart transplantation in adolescent age.

Fig 1. Variant carrying genes.

In DCM-cases TTN carried the most variants. Of 19 TTN-variants in DCM-cases, 6 were truncating variants. The other affected genes were TNNT2, TNNC1, RBM20, PKP2, NEXN, MYL2, MYH7, LMNA, DSP, and DES. In ARVC-cases predominantly PKP2- and TTN-variants were identified. Further variants were found in the genes PRKAG2, PLN, MYH7, MYH6, LMNA, and DES. In the cohort of the RCM-cases variants in 3 different genes were identified: TNNI3, MYL3, and CRYAB. ACMG class 3–5 = variant of uncertain significance, likely pathogenic, pathogenic, respectively.

Fig 2. Distribution of variant classes.

We genotyped 43 index-patients. Of these 18 familial and 6 sporadic cases carried (likely) pathogenic mutations. At least variants of uncertain significance were found in 4 familial and 5 sporadic cases. Only likely benign variants or variants with an allele frequency exceeding the disease prevalence were identified in 10 patients (6 familial, 4 sporadic cases). Familial disposition for the cardiomyopathy is based on pedigree analysis and family reports. Abbreviations: F = familial cases, no label = sporadic cases.

Fig 3. Classification of the variants.

In 60% of DCM- and 40% of ARVC-cases pathogenic and/or likely pathogenic mutations were identified. At least variants with uncertain significance were found in 17% DCM- and 30% ARVC-cases. No relevant variants (MAF >0.0005 in etiological matching controls) were found in 22% and 30% of DCM-, and ARVC-cases, respectively. In RCM-cases, 2 pathogenic and/or likely pathogenic mutations and 1 variant with uncertain significance were identified. Abbreviations: class 2 = likely benign, class 3 = variant of uncertain significance, class 4 = likely pathogenic, class 5 = pathogenic.

Fig 4. Pedigree of DCM-23 family and PKP2 c.2035C>T co-segregation.

A. Family members with HTx were homozygous carriers of PKP2 c.2035C>T, p.His679Tyr whereas heterozygous carriers and the homozygous carrier III/11 had no signs of cardiomyopathy. The LAMA4 variant did not co-segregate with disease (data not shown). Squares = males, circles = females. Deceased individuals are indicated by slashes. Filled symbols indicate individuals with DCM. The index-patient is marked with an arrow. Genotypes are shown by present (+) or by absent (-) of the gene variant. Abbreviations: SCD = sudden cardiac death, SID = sudden infant death, SUD = unexplained sudden death. B. Haplotype analyses of PKP2 c.2035C>T mutation carriers from family DCM-23. Haplotypes associated with the PKP2 mutation are shown in grey shaded areas. These haplotypes are identical in both parents (II/8, II/9) with the exception of marker D12S61. Abbreviation: cM = centimorgan.