Development of left ventricular hypertrophy in adults in hypertrophic cardiomyopathy caused by cardiac myosin-binding protein C gene mutations

OBJECTIVES

We sought to determine whether the development of left ventricular hypertrophy (LVH) can be demonstrated during adulthood in genetically affected relatives with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Hypertrophic cardiomyopathy is a heterogeneous cardiac disease caused by mutations in nine genes that encode proteins of the sarcomere. Mutations in cardiac myosin-binding protein C (MyBPC) gene have been associated with age-related penetrance.

METHODS

To further analyze dormancy of LVH in patients with HCM, we studied, using echocardiography and 12-lead electrocardiography, the phenotypic expression caused by MyBPC mutations in seven genotyped pedigrees.

RESULTS

Of 119 family members studied, 61 were identified with a MyBPC mutation, including 21 genetically affected relatives (34%) who did not express the HCM morphologic phenotype (by virtue of showing normal left ventricular wall thickness). Of these 21 phenotype-negative individuals, 9 were children, presumably in the prehypertrophic phase, and 12 were adults. Of the 12 adults with normal wall thickness < or = 12 mm (7 also with normal electrocardiograms), 5 subsequently underwent serial echocardiography prospectively over four to six years. Of note, three of these five adults showed development of LVH in mid-life, appearing for the first time at 33, 34 and 42 years of age, respectively, not associated with outflow obstruction or significant symptoms.

CONCLUSIONS

In adults with HCM, disease-causing MyBPC mutations are not uncommonly associated with absence of LVH on echocardiogram. Delayed remodeling with the development of LVH appearing de novo in adulthood, demonstrated here for the first time in individual patients with prospectively obtained serial echocardiograms, substantiates the principle of age-related penetrance for MyBPC mutations in HCM. These observations alter prevailing perceptions regarding the HCM clinical spectrum and family screening strategies and further characterize the evolution of LVH in this disease.

Carcinomatous lymphangitis mimicking pulmonary thromboembolism

A 41-year-old woman was admitted with rapidly worsening dyspnea. Echocardiography disclosed interventricular septal flattening and a markedly decreased left ventricle, although left ventricular contraction remained normal. Computed tomography of the chest demonstrated slightly dilated main pulmonary arteries and fine reticulonodular densities in the lung. Examination of a transbronchial lung biopsy specimen revealed carcinomatous lymphangitis, and the patient died 7 days after admission. The clinical presentation of this patient was difficult to discriminate from that seen with pulmonary thromboembolism.

[Genotype-phenotype correlations in familial hypertrophic cardiomyopathy]

Familial hypertrophic cardiomyopathy(FHC) is a complex cardiac disease with unique pathophysiological characteristics and a great diversity of morphological, functional, and clinical features. The results of molecular genetic studies have shown that FHC is a disease of the sarcomere involving eight different genes encoding proteins of the myofibrillar apparatus. Recent advances in genetic studies have provided insights into the heterogeneity of FHC clinical features. Analyses of genotype-phenotype correlations in FHC have shown that the age-related penetrance, the pattern of the left ventricular hypertrophy, and the prognosis are different depending on the disease causing genes or the disease causing mutations. Understanding of the genotype-phenotype correlations in FHC is useful for management of the disease.

Dilated cardiomyopathy in homozygous myosin-binding protein-C mutant mice

To elucidate the role of cardiac myosin-binding protein-C (MyBP-C) in myocardial structure and function, we have produced mice expressing altered forms of this sarcomere protein. The engineered mutations encode truncated forms of MyBP-C in which the cardiac myosin heavy chain-binding and titin-binding domain has been replaced with novel amino acid residues. Analogous heterozygous defects in humans cause hypertrophic cardiomyopathy. Mice that are homozygous for the mutated MyBP-C alleles express less than 10% of truncated protein in M-bands of otherwise normal sarcomeres. Homozygous mice bearing mutated MyBP-C alleles are viable but exhibit neonatal onset of a progressive dilated cardiomyopathy with prominent histopathology of myocyte hypertrophy, myofibrillar disarray, fibrosis, and dystrophic calcification. Echocardiography of homozygous mutant mice showed left ventricular dilation and reduced contractile function at birth; myocardial hypertrophy increased as the animals matured. Left-ventricular pressure-volume analyses in adult homozygous mutant mice demonstrated depressed systolic contractility with diastolic dysfunction. These data revise our understanding of the role that MyBP-C plays in myofibrillogenesis during cardiac development and indicate the importance of this protein for long-term sarcomere function and normal cardiac morphology. We also propose that mice bearing homozygous familial hypertrophic cardiomyopathy-causing mutations may provide useful tools for predicting the severity of disease that these mutations will cause in humans.

Familial dilated cardiomyopathy locus maps to chromosome 2q31

BACKGROUND

Inherited gene defects are an important cause of dilated cardiomyopathy. Although the chromosome locations of some defects and 1 disease gene (actin) have been identified, the genetic etiologies of most cases of familial dilated cardiomyopathy remain unknown.

METHODS AND RESULTS

We clinically evaluated 3 generations of a kindred with autosomal dominant transmission of dilated cardiomyopathy. Nine surviving and affected individuals had early-onset disease (ventricular chamber dilation during the teenage years and congestive heart failure during the third decade of life). The disease was nonpenetrant in 2 obligate carriers. To identify the causal gene defect, linkage studies were performed. A new dilated cardiomyopathy locus was identified on chromosome 2 between loci GCG and D2S72 (maximum logarithm of odds [LOD] score=4.86 at theta=0). Because the massive gene encoding titin, a cytoskeletal muscle protein, resides in this disease interval, sequences encoding 900 amino acid residues of the cardiac-specific (N2-B) domain were analyzed. Five sequence variants were identified, but none segregated with disease in this family.

CONCLUSIONS

A dilated cardiomyopathy locus (designated CMD1G) is located on chromosome 2q31 and causes early-onset congestive heart failure. Although titin remains an intriguing candidate gene for this disorder, a disease-causing mutation is not present in its cardiac-specific N2-B domain.

Proposed standard for human blood vitamin B1 value using HPLC. The Committee for Vitamin Laboratory Standards, Japan

Standard reference ranges for all laboratory test values are mandatory. This study was designed to establish a reference range for blood vitamin B1 levels, since the normal range has not been determined in the Japanese population. We founded the Japan Committee for Vitamin Laboratory Standards, which was incorporated with the Vitamin Society of Japan and the Japanese Society of Nutrition and Food Science. We standardized whole blood vitamin B1 levels using three HPLC techniques (post-column reverse-phase HPLC, pre-column reverse-phase HPLC, and precolumn GP-HPLC). The reference range was obtained in 54 volunteers administered a 1,800 kcal diet with 2 mg of vitamin B1 (1.74 mg measured) daily to avoid marginal vitamin B1 deficiency in the population. The range for each assay was 26-47, 28-51, and 28-56 ng/ml, respectively. Our data suggest that 26-28 ng/ml is the lower limit of normal for whole blood vitamin B1, but further studies in a larger population are needed in order to obtain more definitive results.

Mutations in the gene for cardiac myosin-binding protein C and late-onset familial hypertrophic cardiomyopathy

BACKGROUND

Mutations in the gene for cardiac myosin-binding protein C account for approximately 15 percent of cases of familial hypertrophic cardiomyopathy. The spectrum of disease-causing mutations and the associated clinical features of these gene defects are unknown.

METHODS

DNA sequences encoding cardiac myosin-binding protein C were determined in unrelated patients with familial hypertrophic cardiomyopathy. Mutations were found in 16 probands, who had 574 family members at risk of inheriting these defects. The genotypes of these family members were determined, and the clinical status of 212 family members with mutations in the gene for cardiac myosin-binding protein C was assessed.

RESULTS

Twelve novel mutations were identified in probands from 16 families. Four were missense mutations; eight defects (insertions, deletions, and splice mutations) were predicted to truncate cardiac myosin-binding protein C. The clinical expression of either missense or truncation mutations was similar to that observed for other genetic causes of hypertrophic cardiomyopathy, but the age at onset of the disease differed markedly. Only 58 percent of adults under the age of 50 years who had a mutation in the cardiac myosin-binding protein C gene (68 of 117 patients) had cardiac hypertrophy; disease penetrance remained incomplete through the age of 60 years. Survival was generally better than that observed among patients with hypertrophic cardiomyopathy caused by other mutations in the genes for sarcomere proteins. Most deaths due to cardiac causes in these families occurred suddenly.

CONCLUSIONS

The clinical expression of mutations in the gene for cardiac myosin-binding protein C is often delayed until middle age or old age. Delayed expression of cardiac hypertrophy and a favorable clinical course may hinder recognition of the heritable nature of mutations in the cardiac myosin-binding protein C gene. Clinical screening in adult life may be warranted for members of families characterized by hypertrophic cardiomyopathy.