Fabry disease in patients with hypertrophic cardiomyopathy (HCM)

Fabry disease is an X-linked recessive lysosomal storage disorder with variable phenotype characterized by the accumulation of glycosphingolipid in various tissues. Unlike patients with the classical systemic Fabry disease entity, who present with multiple organ involvement, patients with a cardiac variant of Fabry disease are characterized mainly by myocardial hypertrophy. Therefore, the cardiac variant of Fabry disease may be defined as a cardiomyocytic storage disorder, thus, mimicking the clinical features of hypertrophic obstructive and especially non-obstructive cardiomyopathy. In patients with unexplained left ventricular hypertrophy the diagnosis of a cardiac variant of Fabry disease is performed by light- and electron microscopic evaluation of endomyocardial catheter biopsy specimens and/or serologic investigations (decreased activity of alpha-galactosidase A in plasma or leucocytes). Several studies show that between 4% and 8% of unselected patients with the clinical features of hypertrophic non-obstructive cardiomyopathy have a cardiac variant of Fabry disease. In each patient with unexplained myocardial hypertrophy concealed myocardial storage disease, especially cardiac Fabry disease has to be considered and should be ruled out or confirmed by endomyocardial catheter biopsy. This is important because of the recently reported alpha-galactosidase A enzyme replacement therapy in Fabry disease. Randomized, multicenter studies are mandatory to test the hypothesis that enzyme replacement therapy leads to a beneficial clinical effect in the cardiac variant form of Fabry disease and may prevent the progression of the disease in asymptomatic patients.     

Fabry disease female proband with clinical manifestations similar to hypertrophic cardiomyopathy

Fabry's disease is an X-linked inborn error of glycosphingolipid catabolism, resulting from a deficiency in alpha-galactosidase A (alpha-Gal A). A 56-year-old Japanese woman was at first suspected of having hypertrophic cardiomyopathy. The patient and her son had alpha-Gal A activity in leukocytes that was remarkably below the limit of controls. DNA analysis of the alpha-Gal A gene revealed a novel missense mutation at codon 19 in exon 1, resulting in leucine-to-proline substitution. As a result she was confirmed as a classic Fabry heterozygote. Recent advances in enzyme replacement therapy can reverse the storage of glycosphingolipids in Fabry's disease. Thus, in patients with cardiac hypertrophy, it is important to differentiate Fabry's disease from other causes of hypertrophy. Therefore, it is necessary to measure alpha-Gal A activity in all suspected cases and to analyze genetic abnormalities in heterozygotes.     

肥厚型心肌病样临床表现的Fabry病家系研究

目的对一个临床表现酷似肥厚型心肌病的Fabry病家系进行α-半乳糖苷酶（α-GalA）基因测序并发现其突变形式。方法该家系成员共15例,经过询问病史、体格检查、心电图及超声心动图检查,抽取外周静脉血标本,提取白细胞基因组DNA,PCR分段扩增α-GalA基因的7个外显子序列,产物纯化后直接测序,分析筛查基因的突变位点。结果家系中有9例发生α-GalA基因新的错义突变,突变位点位于α-GalA基因第5外显子的第32号密码子,均由TGG变为TGA,TGA为终止密码子,故可引起TGG正常编码的色氨酸残基编码中断。其中6例女性为带有突变基因的杂合子,3例男性为带有突变基因的半合子。9例患者中6例患有心肌肥厚。家系中正常人无此类突变。结论对心肌肥厚患者应与Fabry病进行鉴别诊断。α-GalA基因突变检测可用于Fabry病患者及其亲属,以明确诊断和进行病因学治疗。     

The genetic basis of hypertrophic cardiomyopathy.

In this article we review the techniques of molecular biology as they apply to the elucidation of the genetic basis of hypertrophic cardiomyopathy. We review the evidence for linkage to chromosome 14 and the specific mutations described to date. The evidence for genetic heterogeneity is presented. We speculate on the pathophysiology of the disease from the perspective of the known molecular defects and review the clinical implications the evolving information may have.     

The molecular genetic basis for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), a relatively common disease, is diagnosed clinically by unexplained cardiac hypertrophy and pathologically by myocyte hypertrophy, disarray, and interstitial fibrosis. HCM is the most common cause of sudden cardiac death (SCD) in the young and a major cause of morbidity and mortality in elderly. Hypertrophy and fibrosis are the major determinants of morbidity and SCD. More than 100 mutations in nine genes, all encoding sarcomeric proteins have been identified in patients with HCM, which had led to the notion that HCM is a disease of contractile sarcomeric proteins. The beta -myosin heavy chain (MyHC), cardiac troponin T (cTnT) and myosin binding protein-C (MyBP-C) are the most common genes accounting for approximately 2/3 of all HCM cases. Genotype-phenotype correlation studies suggest that mutations in the beta -MyHC gene are associated with more extensive hypertrophy and a higher risk of SCD as compared to mutations in genes coding for other sarcomeric proteins, such as MyBP-C and cTnT. The prognostic significance of mutations is related to their hypertrophic expressivity and penetrance, with the exception of those in the cTnT, which are associated with mild hypertrophic response and a high incidence of SCD. However, there is a significant variability and factors, such as modifier genes and probably the environmental factors affect the phenotypic expression of HCM. The molecular pathogenesis of HCM is not completely understood. In vitro and in vivo studies suggest that mutations impart a diverse array of functional defects including reduced ATPase activity of myosin, acto-myosin interaction, cross-bridging kinetics, myocyte contractility, and altered Ca2+ sensitivity. Hypertrophy and other clinical and pathological phenotypes are considered compensatory phenotypes secondary to functional defects. In summary, the molecular genetic basis of HCM has been identified, which affords the opportunity to delineate its pathogenesis. Understanding the pathogenesis of HCM could provide for genetic based diagnosis, risk stratification, treatment and prevention of cardiac phenotypes.     

Importance of the genetic aspect in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a disease characterised by massive ventricular hypertrophy, reduced diastolic function and excessive ventricular contraction. It involves sections of both ventricles, but in particular the left ventricle. Although it was initially thought that this pathology might depend on a modified systolic function, it is now widely held that the main alteration is of a diastolic type. The paper focuses on the importance of the genetic component in this cardiopathy, and stresses that the majority of patients affected by this disease and examined by the Authors had positive family histories, in line with previously published reports. In the majority of cases the pathology is transmitted in a dominant autosomic manner, although there are also sporadic episodes of non-hereditary transmission due to genetic mutation.     

Amyloid heart disease mimicking hypertrophic cardiomyopathy

OBJECTIVE: To investigate the importance of transthyretin (TTR) gene mutations in explaining the phenotypic expression in patients diagnosed with hypertrophic cardiomyopathy (HCM) in northern Sweden. BACKGROUND: Hypertrophic cardiomyopathy is relatively common and often caused by mutations in sarcomeric protein genes. Mutations in the TTR gene are also common, one of which causes familial amyloid polyneuropathy (FAP), with peripheral polyneuropathy and frequently, cardiac hypertrophy. These circumstances were highlighted by the finding of an index case with amyloidosis, presenting itself as HCM. Initial rectal and fat biopsies did not show amyloid deposits. Later on, the patient was shown to carry a TTR gene mutation, and cardiac amyloidosis was confirmed by myocardial biopsy. Only then was a repeated fat biopsy positive for amyloid deposits. DESIGN: Cross-sectional study. SETTING: Cardiology tertiary referral centre. SUBJECTS: Forty-six unrelated individuals with HCM and the index case were included. Common diagnostic criteria for HCM were used. The 46 patients with HCM were previously analysed for mutations in eight sarcomeric protein genes and the TTR gene was now analysed by denaturing high-performance liquid chromatography and direct sequencing. RESULTS: One mutation in the TTR gene (Val30Met) was found in three individuals and the index case. CONCLUSIONS: Three of the 46 cases with HCM carried the Val30Met mutation, and were considered likely to have cardiac amyloidosis, like the index case. As a correct diagnosis of cardiac amyloidosis is mandatory for a potentially life-saving treatment, TTR mutation analysis should be considered in cases of HCM not explained by mutations in sarcomeric protein genes.     

Value of electrocardiogram in the differentiation of hypertensive heart disease, hypertrophic cardiomyopathy, aortic stenosis, amyloidosis, and Fabry disease

Left ventricular hypertrophy is 1 of the most frequent cardiac manifestations associated with an unfavorable prognosis. However, many different causes of left ventricular hypertrophy exist. The aim of the present study was to assess the diagnostic value of common electrocardiographic (ECG) parameters to differentiate Fabry disease (FD), amyloidosis, and nonobstructive hypertrophic cardiomyopathy (HC) from hypertensive heart disease (HHD) and aortic stenosis (AS). In 94 patients with newly diagnosed FD (n = 17), HHD (n = 20), amyloidosis (n = 17), AS (n = 20), and HC (n = 20), common ECG parameters were analyzed and tested for their diagnostic value. A stepwise approach including the Sokolow-Lyon index, corrected QT duration, and PQ interval minus P-wave duration in lead II to overcome P-wave abnormalities was applied. A corrected QT duration <440 ms in combination with a PQ interval minus P-wave duration in lead II <40 ms was 100% sensitive and 99% specific for the diagnosis of FD, whereas a corrected QT duration >440 ms and a Sokolow-Lyon index ≤1.5 mV were found to have a sensitivity and specificity of 85% and 100%, respectively, for the diagnosis of amyloidosis and differentiation from HC, AS, and HHD. Moreover, a novel index ([PQ interval minus P-wave duration in lead II multiplied by corrected QT duration]/Sokolow-Lyon index) proved to be highly diagnostic for the differentiation of amyloidosis (area under the curve 0.92) and FD (area under the curve 0.91) by receiver operator characteristic analysis. In conclusion, a combined analysis of PQ interval minus P-wave duration in lead II, corrected QT duration, and Sokolow-Lyon index proved highly sensitive and specific in the differentiation of FD, amyloidosis, and HC compared to HHD and AS. Analysis of these easy-to-assess ECG parameters may be of substantial help in the diagnostic workup of these 5 conditions.     

Clinical and genetic aspects of hypertrophic and dilated cardiomyopathy

Primary cardiomyopathies are frequent heart diseases with an estimated prevalence of 0.3-0.4% in the general population, significantly contributing to systolic heart failure and sudden cardiac death in the young. Molecular genetic studies have identified 49 different disease genes for hypertrophic and dilated cardiomyopathy, often involving proteins of the sarcomere, the cardiac Z-disc and the cytoskeleton. With the development of new, advanced technologies based on next-generation sequencing, it is now possible to efficiently screen all known disease genes in an individual patient. The clinical workup of cardiomyopathies should always include the investigation of the patient's family to account for the familial aggregation of cardiomyopathies and identify diseased as well as asymptomatic carriers of mutations. The detection of specific genotypes facilitates diagnostic classification and can improve risk stratification in affected patients.