Genotype, phenotype and disease severity reflected by serum LysoGb3 levels in patients with Fabry disease
Introduction
Fabry disease (FD) (OMIM# 301500) is an X-linked disease, resulting from the deficient activity of the lysosomal enzyme α-galactosidase A (α-Gal A) [1], [2]. The enzymatic defect causes the progressive accumulation of globotriaosylceramide (Gb3) and related glycosphingolipids in the plasma and in tissue lysosomes throughout the body [1].
There are two major phenotypes, Classic and Later-Onset [1], [3], [4], [5], [6]. The Classic phenotype is more severe due to very low or absent α-Gal A activity, with the typical early symptoms such as acroparesthesias, angiokeratoma, corneal opacities and hypohidrosis, particularly in males. With advancing age, the progressive deposition of glycosphingolipids lead to cardiomyopathy, deterioration of kidney function, and premature strokes [7], [8]. The Later-Onset phenotype is typically less severe with a significant residual α-Gal A activity in males, who usually lack the early symptoms but present with a cardiomyopathy or chronic kidney disease in the adult age [3], [9], [10], [11].
The phenotypic heterogeneity can delay the correct diagnosis. In females, α-Gal A activity can be normal due to random X-chromosomal inactivation [12]. Even genetic testing can result in novel GLA variants with unknown clinical significance [13]. This raises questions with regard to disease onset and progression, particularly in asymptomatic patients identified in family screening.
Recently, enhanced deposits of globotriaosylsphingosine (LysoGb3) have been shown to be a characteristic feature of FD [14]. The deacylated Gb3, LysoGb3 (also called LysoGl3), also known as globotriaosylsphingosine, has been reported as a potential diagnostic tool in both classic and uncertain cases [15]. The utility of LysoGb3 is still controversial, as discussed in previous studies [15], [16], due to concerns that LysoGb3 levels may not be strongly associated with disease phenotype [17]. To answer these concerns, we evaluated whether a genotype/phenotype association can be established using serum LysoGb3 levels. To this end, we analyzed a clinical, biochemical and genetic characterization of a large FD patient's cohort that was regularly monitored at a single FD center. This is the first study to associate LysoGb3 levels with the FD-related comorbidities and the genotype severity.
Section snippets
Study participants and clinical work-up
The study was conducted in accordance with the principles of the Helsinki Declaration. Informed consent for collecting clinical data and blood samples for biobanking was obtained from all patients.
We recruited 69 consecutive adult patients (males: n = 28 (41%)) at the University Hospital Zurich, Switzerland, between January 2014 and December 2016. All patients had a confirmed GLA-mutation diagnosis and presented for routine annual examinations at our FD center. The cohort was established in 2001
Baseline characteristics
The baseline characteristics and sex of all patients are presented in Table 1. In male patients, serum creatinine levels were higher and cardiomyopathy more frequent than in female patients. All patients on renal replacement therapy were male.
LysoGb3 in relation to sex and phenotype
In males and females, serum levels of LysoGb3 were significantly higher in Classic than in Later-Onset phenotype patients. In healthy controls, LysoGb3 levels were lower than in FD patients (Fig. 1A and B).
There was one overlap in LysoGb3 levels between
Discussion
In this relatively large and well characterized cohort of genetically proven FD patients, serum levels of LysoGb3 were significantly higher than in the healthy controls. More importantly, LysoGb3 levels were significantly higher in the Classic than in the Later-Onset phenotype in male and female patients. After adjustment for sex and phenotype, LysoGb3 was independently associated with the relevant co-morbidities such as kidney function, renal replacement therapy, cardiomyopathy, stroke and TIA.
Role of the funding source
The LysoGb3 measurements were determined by ARCHIMED Life Science, Vienna, Austria. The ARCHIMED Life Science laboratory members (TPM and DCK) participated in writing and approving the manuscript. The laboratory members were blinded to patients' names and all clinical and biochemical information and had no role in the collection of samples, interpretation of data and the decision to submit the article for publication.
Conflict of interest
AN is a consultant to Shire, received lecturing honoraria and research support from Sanofi Genzyme and Shire and received financial publication support of this paper from Sanofi Genzyme.
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