Deciphering the diagnostic dilemma: A comprehensive review of the Taiwanese cardiac variant in Fabry disease.

Molecular diagnosis has undergone rapid and significant advancements in recent years. But because molecular diagnosis can be conducted independently of phenotype, it can engender ambiguity and potential misinterpretations in disease diagnosis. Fabry disease, an X-linked lysosomal storage disorder, arises from a deficiency in α-galactosidase A. In 2002, Ishii and colleagues uncovered a variant (IVS4+919G > A) deep within intron 4 of the GLA gene that could lead to aberrant splicing of the GLA mRNA. This variant is present in 1:875 males in Taiwan, and many patients with hypertrophic cardiomyopathy and the IVS4+919G > A variant are currently treated by enzyme replacement therapy, an expensive treatment. Unfortunately, till now only one article published in 2013 described the outcome of treatment. This review summarized the conflicting evidence about the clinical relevance of the IVS4+919G > A variant, and suggest a multifactorial model, rather than a monogenic model, for the involvement of the IVS4+919G > A variant in hypertrophic cardiomyopathy. The diagnostic dilemma for this Taiwanese cardiac variant in Fabry disease clearly emphasizes the need for precise interpretation and application of molecular diagnostic results.

2021 TSOC Expert Consensus on the Clinical Features, Diagnosis, and Clinical Management of Cardiac Manifestations of Fabry Disease.

Fabry disease (FD) is an X-linked, rare inherited lysosomal storage disease caused by α-galactosidase A gene variants resulting in deficient or undetectable α-galactosidase A enzyme activity. Progressive accumulation of pathogenic globotriaosylceramide and its deacylated form globotriaosylsphingosine in multiple cell types and organs is proposed as main pathophysiology of FD, with elicited pro-inflammatory cascade as alternative key pathological process. The clinical manifestations may present with either early onset and multisystemic involvement (cutaneous, neurological, nephrological and the cardiovascular system) with a progressive disease nature in classic phenotype, or present with a later-onset course with predominant cardiac involvement (non-classical or cardiac variant; e.g. IVS4+919G>A in Taiwan) from missense variants. In either form, cardiac involvement is featured by progressive cardiac hypertrophy, myocardial fibrosis, various arrhythmias, and heart failure known as Fabry cardiomyopathy with potential risk of sudden cardiac death. Several plasma biomarkers and advances in imaging modalities along with novel parameters, cardiac magnetic resonance (CMR: native T1/T2 mapping) for myocardial tissue characterization or echocardiographic deformations, have shown promising performance in differentiating from other etiologies of cardiomyopathy and are presumed to be helpful in assessing the extent of cardiac involvement of FD and in guiding or monitoring subsequent treatment. Early recognition from extra-cardiac red flag signs either in classic form or red flags from cardiac manifestations in cardiac variants, and awareness from multispecialty team work remains the cornerstone for timely managements and beneficial responses from therapeutic interventions (e.g. oral chaperone therapy or enzyme replacement therapy) prior to irreversible organ damage. We aim to summarize contemporary knowledge based on literature review and the gap or future perspectives in clinical practice of FD-related cardiomyopathy in an attempt to form a current expert consensus in Taiwan.

Biomarkers associated with clinical manifestations in Fabry disease patients with a late-onset cardiac variant mutation.

BACKGROUND: Fabry disease is a lysosomal storage disorder with an incidence of 1:1600 for the late-onset IVS4+919G>A cardiac variant mutation in Taiwan. Signs and symptoms of this cardiac variant include left ventricular hypertrophy, mitral insufficiency and/or arrhythmias. The search for biomarkers that might predict the clinical outcomes and guide treatment options is important. We thus investigated relationships between Fabry disease biomarkers (such as globotriaosylceramide (Gb3), globotriaosylsphingosine (lyso-Gb3)/related analogues) and age, gender, enzyme activity, clinical manifestations and severity of the disease in these patients. METHOD: Urine and plasma biomarkers were analyzed using tandem mass spectrometry. A large cohort of 191 adult and pediatric Fabry patients carrying the IVS4+919G>A mutation was studied. Some patients were members of the same family. RESULTS: Our results show that the plasma lyso-Gb3 level, and urinary analogue levels of lyso-Gb3 at m/z (+16), (+34), and (+50) adjusted for gender and age had a positive association with the left ventricular mass index, and/or the Mainz Severity Score Index. CONCLUSIONS: It might thus be of particular interest to monitor children with high levels of these biomarkers, as part of a longitudinal study in order to determine if the excretion profile at a young age is predictive of the outcomes of disease severity in adulthood.

Later Onset Fabry Disease, Cardiac Damage Progress in Silence: Experience With a Highly Prevalent Mutation.

BACKGROUND: Recently, several studies revealed a much higher prevalence of later onset Fabry disease (FD) than previously expected. It suggested that later onset FD might present as an important hidden health issue in certain ethnic or demographic populations in the world. However, the natural history of its phenotype has not been systemically investigated, especially the cardiac involvement. OBJECTIVES: The study analyzed a large-scale newborn screening program for FD to understand the natural course of later onset FD. METHODS: To date, 916,383 newborns have been screened for FD in Taiwan, including more than 1,200 individuals with the common, later onset IVS4+919G>A (IVS4) mutation. Echocardiography was performed in 620 adults with the IVS4 mutation to analyze the prevalence of left ventricular hypertrophy (LVH), and gadolinium-enhanced cardiac magnetic resonance imaging was performed in 129 patients with FD, including 100 IVS4 adults. RESULTS: LVH was observed in 67% of men and 32% of women older than 40 years. Imaging evidenced significant late gadolinium enhancement in 38.1% of IVS4 men and 16.7% of IVS4 women with the IVS4 mutation but without LVH. Seventeen patients underwent endomyocardial biopsies, which revealed significant globotriaosylceramide substrate accumulation in their cardiomyocytes. CONCLUSIONS: Significant cardiomyocyte substrate accumulation in IVS4 patients led to severe and irreversible cardiac fibrosis before development of LVH or other significant cardiac manifestations. Thus, it might be too late to start enzyme replacement therapy after the occurrence of LVH or other significant cardiac manifestations in patients with later onset FD. This study also indicated the importance of newborn screening for early detection of the insidious, ongoing, irreversible cardiac damage in patients with later onset FD.

Plasma globotriaosylsphingosine (lysoGb3) could be a biomarker for Fabry disease with a Chinese hotspot late-onset mutation (IVS4+919G>A).

BACKGROUND: Previous studies revealed a high incidence of late-onset Fabry disease mutation, IVS4+919G>A, in Taiwan. However, the natural course is largely unclear and suitable biomarkers for monitoring disease progress are unavailable. METHODS AND RESULTS: Patients carrying IVS4+919G>A or classical Fabry mutations were enrolled in this study. The subjects ranged from newborn to eighty year old adults. Plasma globotriaosylceramide (Gb3) and globotriaosylsphingosine (lysoGb3) were measured by LC-MS/MS in subjects to evaluate the sensitivity of these two biomarkers. All adult males and symptomatic females could be distinguished from healthy controls by an elevated plasma lysoGb3 level. The lysoGb3 level was also related to the left ventricular mass considering gender and age (p<0.01). Moreover, approximately 70% of male and 45% of female newborns already had an elevated plasma lysoGb3 level which increased gradually as the subjects got older (p<0.01). CONCLUSIONS: Plasma lysoGb3 is a more sensitive and reliable biomarker than plasma Gb3. LysoGb3 also correlated with age and left ventricular mass index in Fabry patients with IVS4+919G>A mutation. Because lots of infants with the IVS4+919G>A mutation already had elevated lysoGb3 levels at birth, that indicates that the development of hypertrophic cardiomyopathy may require a long and insidious course after lysoGb3 accumulation.

Effects of enzyme replacement therapy for cardiac-type Fabry patients with a Chinese hotspot late-onset Fabry mutation (IVS4+919G>A).

OBJECTIVE: Current studies of newborn screening for Fabry disease in Taiwan have revealed a remarkably high prevalence of cardiac-type Fabry disease with a Chinese hotspot late-onset Fabry mutation (IVS4+919G>A). DESIGN: Retrospective cohort study. SETTING: Tertiary medical centre. PARTICIPANTS: 21 patients with cardiac-type Fabry disease (15 men and 6 women) as well as 15 patients with classic Fabry disease (4 men and 11 women) treated with biweekly intravenous infusions of agalsidase ß (1 mg/kg) or agalsidase α (0.2 mg/kg) for at least 6 months. OUTCOME MEASURES: These data were collected at the time before enzyme replacement therapy (ERT) began and followed up after ERT for at least 6 months, including patient demographics, medical history, parameter changes of cardiac status and renal functions, plasma globotriaosylsphingosine (lyso-Gb3) and Mainz Severity Score Index. RESULTS: After 6-39 months of ERT, plasma lyso-Gb3 was found to be reduced in 89% (17/19) and 93% (14/15) of patients with cardiac-type and classic Fabry disease, respectively, which indicated an improvement of disease severity. For patients with cardiac-type Fabry disease, echocardiography revealed the reduction or stabilisation of left ventricular mass index (LVMI), the thicknesses of intraventricular septum (IVS) and left posterior wall (LPW) in 83% (15/18), 83% (15/18) and 67% (12/18) of patients, respectively, as well as 77% (10/13), 73% (11/15) and 60% (9/15) for those with classic type. Most patients showed stable renal function after ERT. There were statistically significant improvements (p<0.05) between the data at baseline and those after ERT for values of plasma lyso-Gb3, LVMI, IVS, LPW and Mainz Severity Score Index. No severe clinical events were reported during the treatment. CONCLUSIONS: ERT is beneficial and appears to be safe for Taiwanese patients with cardiac-type Fabry disease, as well as for those with the classic type.