A variant of unknown significance in the GLA gene causing diagnostic uncertainty in a young female with isolated hypertrophic cardiomyopathy

doi:10.1016/j.gene.2012.01.056

Gene

Volume 497, Issue 2, 15 April 2012, Pages 320-322

https://doi.org/10.1016/j.gene.2012.01.056 Get rights and content

Abstract

Hypertrophic cardiomyopathy (HCM) is genetically heterogeneous, and largely caused by mutations in genes encoding sarcomere proteins. However, GLA mutations causing Fabry disease, an X-linked lysosomal storage disorder, may also present with isolated HCM. As HCM genetic testing panels are increasingly being used clinically, variants of unknown significance (VUS) are encountered, leading to challenges in interpretation. We present an illustrative case: a 10-year-old girl with isolated HCM who, on testing with a HCM multi-gene panel, was found to carry a maternally inherited p.W24R variant in GLA. Attempts to evaluate the significance of this variant, by direct biochemical testing of patient specimens, gave inconclusive results. Subsequent in vitro protein expression studies suggested that the variant is unlikely to be pathogenic. This case highlights diagnostic dilemmas that can be provoked by VUS in general, and specifically raises a question whether GLA sequencing should be included in first-line diagnostic testing for female children with isolated hypertrophic cardiomyopathy.

Highlights

► Functional analysis of a variant of unknown significance (VUS). ► Reviewing the natural history of hypertrophic cardiomyopathy in Fabry disease. ► Discussing challenges created by VUS in clinically variable disorders.

Introduction

Hypertrophic cardiomyopathy (HCM) affects about 1 in 500 individuals (Maron et al., 1995), and is genetically heterogeneous. Fabry disease (FD) is an X-linked lysosomal storage disorder, due to the deficient activity of α-galactosidase A caused by mutations in the GLA gene. While classical FD is a multi-system disorder, some patients with FD present with isolated HCM. Three percent of males with left ventricular hypertrophy (LVH), and up to 6% of men diagnosed with HCM after 40 years of age have FD (Nakao et al., 1995, Sachdev et al., 2002). A proportion of females diagnosed with HCM above the age of 40 years have FD (Chimenti et al., 2004). Differentiating FD from other genetic causes of HCM on clinical grounds can be very difficult. Such a distinction is clinically significant as FD is specifically treatable with enzyme replacement therapy, while cardiac medications commonly used in the treatment of HCM may be contraindicated in FD. Therefore some genetic testing panels clinically available for HCM include GLA, in addition to sarcomere-related genes which are more common causes of inherited HCM. Such panels offer a non-invasive route to resolve the differential diagnosis; however, it is not uncommon to encounter newly-identified variants, leading to challenges in evaluating their clinical significance. The case which we report demonstrates significant diagnostic challenges and dilemmas that resulted from a variant of unknown significance (VUS) in GLA identified by an HCM genetic testing panel.

Section snippets

Case report

A 10 year old girl was referred to the Pediatric Cardiology Clinic at British Columbia Children's Hospital (BCCH) for evaluation of a few weeks' history of exertional dyspnea and generalized fatigue. An ECG showed sinus rhythm with evidence of marked atrial hypertrophy, right axial deviation, right bundle branch block, and T-wave inversion in inferior leads. Chest X ray showed cardiomegaly, and echocardiography showed symmetric hypertrophy of the left and right ventricles with dilatation of the

Discussion

Evaluating potential pathogenicity of the variant identified in this patient was hampered by multiple challenges. Firstly, she belongs to a small family and is apparently the only affected individual. While the same variant was identified in the patient's 45-year-old mother, who has no evidence of HCM at present, this does not rule out pathogenicity of the variant, given the known intrafamilial variability of presentation of Fabry disease due in part to variable patterns of X inactivation.

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Cited by (5)

A novel double GLA gene mutation of W24R and N419D in a patient with cardiac Fabry disease
2023, Molecular Genetics and Metabolism Reports
Fabry disease (FD) is an X-linked lysosomal storage disorder caused by insufficient activity of α-galactosidase A (α-Gal A) encoded by GLA. The enzymatic defect causes the progressive accumulation of sphingolipids in various tissues and body fluids, causing systemic disorders. We report a rare familial case of inherited cardiac FD associated with a novel double mutation in the GLA gene: W24R and N419D.
A young man with severe obesity was admitted for heart failure (HF) with the diagnosis of dilated cardiomyopathy. Left ventricular hypertrophy was suspected during HF treatment after discharge, and in association with his mother's family history of cardiac diseases and sudden death, the etiology of the hypertrophy was re-examined. Very low α-Gal A activity confirmed the diagnosis of FD. Gene mutation analysis of GLA demonstrated a double mutation: W24R and N419D. Proband analysis revealed the same double mutation in his mother. Although she had no signs or symptoms of FD, we detected mild accumulation of globotriaosylsphingosine. The good laboratory practice-validated assay using HEK293 cells showed that the double mutation was amenable to migalastat, a pharmacological chaperone stabilizing α-Gal A.
This case highlights a novel double gene mutation in GLA (W24R and N419D) identified in a family with FD. Although clinical significance of each mutation remains unknown, its combination might work synergistically to attain or augment pathogenicity.
The Clinician-reported Genetic testing Utility InDEx (C-GUIDE): Preliminary evidence of validity and reliability
2022, Genetics in Medicine
Citation Excerpt :
We developed 19 unique patient vignettes (Supplemental Material - Vignettes) to mimic the clinical scenarios for which C-GUIDE was designed. A geneticist worked with the study team to draft the vignettes; some were also informed by case reports in the literature.21-25 All vignettes provided explicit details about the diagnostic, prognostic, management, reproductive, or psychosocial impact of genetic test results to enable raters to respond to all C-GUIDE items (Version 1.1).
Demonstrating the clinical utility of genetic testing is fundamental to clinical adoption and reimbursement, but standardized definitions and measurement strategies for this construct do not exist. The Clinician-reported Genetic testing Utility InDEx (C-GUIDE) offers a novel measure to fill this gap. This study assessed its validity and inter-rater reliability.
Genetics professionals completed C-GUIDE after disclosure of test results to patients. Construct validity was assessed using regression analysis to measure associations between C-GUIDE and global item scores as well as potentially explanatory variables. Inter-rater reliability was assessed by administering a vignette-based survey to genetics professionals and calculating Krippendorff’s α.
On average, a 1-point increase in the global item score was associated with an increase of 3.0 in the C-GUIDE score (P < .001). Compared with diagnostic results, partially/potentially diagnostic and nondiagnostic results were associated with a reduction in C-GUIDE score of 9.5 (P < .001) and 10.2 (P < .001), respectively. Across 19 vignettes, Krippendorff’s α was 0.68 (95% CI: 0.63-0.72).
C-GUIDE showed acceptable validity and inter-rater reliability. Although further evaluation is required, C-GUIDE version 1.2 can be useful as a standardized approach to assess the clinical utility of genetic testing.
Enzymatic diagnosis of Fabry disease using a fluorometric assay on dried blood spots: An alternative methodology
2013, European Journal of Medical Genetics
Citation Excerpt :
Interestingly, we recently demonstrated that Sanger sequencing can be performed using DBS as the source of DNA for PCR amplification (Hagege et al., 2011). The rapid development of massively parallel sequencing may soon provide an interesting alternative for sequencing individuals at risk of Fabry disease with the inclusion of GLA in gene panels, although the incidental discovery of variant of unknown significance may occasionally lead to diagnostic uncertainty (Al-Thihli et al., 2012). The modified method was successfully used for the screening of FD in patients with hypertrophic cardiomyopathy.
Fabry disease (FD, OMIM#301500) is an X-linked lysosomal storage disorder caused by the functional deficiency of α-galactosidase A, a lysosomal enzyme. A method to screen for FD in large populations has been developed using a fluorometric assay of α-galactosidase A activity in dried blood spots (DBS) on filter paper. However, results can be influenced by quenching of fluorescence by haemoglobin which, together with small sample size, may result in a low light emission signal.
An alternative, simple and sensitive fluorometric assay was developed for the determination of α-galactosidase A activity in DBS. The assay uses 4-methylumbelliferyl-α-d-galactose as an artificial substrate. To minimize the risk of false-positives, zinc sulfate was used for protein precipitation to stop the enzymatic reaction and eliminate interfering species (hemoglobin). Samples from 209 individuals (60 hemizygotes, 68 heterozygotes, and 81 controls) were tested to establish reference values for the assay.
The mean α-galactosidase A activity of the 81 controls was 9.1 ± 3.3 μmol h⁻¹ L⁻¹ (mean ± SD). All 60 hemizygotes affected with FD had AGAL activities below 1.7 μmol h⁻¹ L⁻¹ (0.2 ± 0.3 μmol h⁻¹ L⁻¹). For the 68 heterozygous females, AGAL activity ranged from 0 to 12.6 μmol h⁻¹ L⁻¹ (3.5 ± 2.7 μmol h⁻¹ L⁻¹). Two-thirds of the female patients could be identified using the enzymatic assay and a cut-off level of 40% of the median control value (<3.4 μmol h⁻¹ L⁻¹).
Our fluorometric assay using zinc sulfate protein precipitation was shown to have similar sensitivity and robustness while reducing the risk of false positive results due to quenching of 4-MU fluorescence by haemoglobin.
Heart disease in disorders of muscle, neuromuscular transmission, and the nerves
2016, Korean Circulation Journal
Fabry disease: A review of current enzyme replacement strategies
2015, Expert Opinion on Orphan Drugs

¹: Current address: Genetic and Developmental Medicine Clinic, Sultan Qaboos University Hospital, P.O. Box 38, P.C 123, AlKhod, Oman.

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Short CommunicationA variant of unknown significance in the GLA gene causing diagnostic uncertainty in a young female with isolated hypertrophic cardiomyopathy

Abstract

Highlights

Introduction

Section snippets

Case report

Discussion

Mol. Genet. Metab.

J. Am. Coll. Cardiol.

Mol. Genet. Metab.

Prevalence of Fabry disease in female patients with late-onset hypertrophic cardiomyopathy

Circulation

Delayed-enhanced cardiac MRI for differentiation of Fabry's disease from symmetric hypertrophic cardiomyopathy AJR

Am. J. Roentgenol.

Human Splicing Finder: an online bioinformatics tool to predict splicing signals

Nucleic Acids Res.

Short Communication
A variant of unknown significance in the GLA gene causing diagnostic uncertainty in a young female with isolated hypertrophic cardiomyopathy