A Case Study of Fabry Nephropathy and Its Progression: the First Reported Case in Malaysia

Fabry disease (FD) is a rare metabolic disorder caused by the genetic deficiency of the lysosomal hydrolase alpha-galactosidase A, causing common and serious kidney complications. We report the first case of Fabry disease detected in Malaysia. A 35-year-old man had an incidental finding of proteinuria during routine health screening. His symptoms included frothy urine and intermittent lower limb swelling. Renal biopsy showed features of Fabry’s disease which was confirmed with genetic testing. He had classical hemizygous Fabry disease of c.610 C > T with Fabry nephropathy, cardiomyopathy, and cornea verticillata. He was then started on enzyme replacement therapy (ERT) with agalsidase till date. Proteinuria is the predominant factor in Fabry nephropathy predicting renal disease progression rate. Early Fabry disease diagnosis could prevent kidney disease progression through the timely initiation of treatment which will help enhance the quality of life of the patient, as the disease progresses.

profile was normal [initial serum creatinine 63 umol/L, estimated glomerular filtration rate (eGFR) 118 mL/min/1.73m 2 with the CKD-Epi formula)]. Twenty-four-hour urine protein was 1.19 g/L with no kidney structural abnormalities being detected by ultrasonography (right and left kidney sizes measuring11.3 cm and 12.0 cm, respectively). The serum albumin was 39 g/dL with a normal total cholesterol level. He was seronegative for syphilis, human immunodeficiency virus (HIV), and hepatitis B and C. Autoimmune screening was negative.
During follow-up, his proteinuria worsened with 24-h urine protein rising to 2.8 g/L 4 years later. He remained normotensive and euglycemic with no evidence of retinopathy. In view of persistent unexplained proteinuria, renal biopsy ( Fig. 1) was performed which showed prominent podocytes with expanded abundant cytoplasm that appears pale with fine vacuolation forming a lacy appearance. There was also moderate intimal thickening of the artery and small foci of tubular atrophy surrounded by interstitial fibrosis seen under microscopy. The immunofluorescence staining for (Ig) G, Ig A, Ig M, (C)3, and C1q was negative. Hence, FD was highly suspected from the overall findings.
A blood sample for Lysosomal Enzymes Assay Test was subsequently sent. Plasma alpha-galactosidase A (AGAL) zero nmol/mL/hour (normal reference 2-10). A genetic study (GLA gene variant analysis) was conducted based on polymerase chain reaction (PCR) amplification and sequencing methods, confirming the fact that our patient was hemizygous for pathogenic p.Trp204Arg variant (c.610 T > C) in the GLA gene, consistent with a final diagnosis of Fabry disease.
Serial system-based physical and ancillary investigations were performed to assess the end-organ involvement of FD. Cornea verticillata was noted in both eyes via slitlamp examination. Transthoracic echocardiogram showed moderate concentric left ventricular hypertrophy (LVH) with LV ejection fraction above 55%. The other organ systems including neurology, cutaneous, ears, gastrointestinal tract, cerebrovascular, and psychology were unremarkable. Hence, a final diagnosis of FD with renal, ocular, and cardiovascular was made.
He was then commenced on ERT-intravenous agalsidase beta (Fabrazyme®) manufactured by Sanofi with a dose of 35 mg twice weekly for the first two doses, followed by the maintenance regimen of 70 mg (1 mg/kg) every 2 weeks 5 years after the FD diagnosis was made and almost a decade after his initial presentation. He was also started on low-dose perindopril (a type of angiotensin-converting enzyme ACE inhibitor) for his proteinuria. He remained on these treatments with normal blood pressure to date (approximately 2 years post-ERT commencement). The serial investigation is shown in Table 1.
His proteinuria showed no improvement despite starting on ERT and kidney function also showed deterioration of 4.3 mL/min/1.73m 2 per year. However, extrarenal manifestation and cardiomyopathy showed improvement, whereby a repeated echocardiogram in 2019 showed normal left ventricular cavity size and normal wall thickness.
He has 2 younger brothers and 1 younger sister. Enzyme and genetic studies were performed for the siblings using dry blood spots with capillary blood. His younger brother and sister were detected to have FD through the screening with heterozygous mutation of p.Trp204Arg. His mother was also found to have a similar mutation.
He has 5 children: 1 son and 4 daughters. His son was tested but was found to be healthy. However, 4 of his daughters were detected to have a heterozygous mutation  for p.Trp204Arg. His son was not affected as expected. A son and a daughter of his sister were affected by a similar mutation. This is illustrated in Fig. 2.

Discussion
Fabry nephropathy is common in Fabry's disease. Typically, Fabry nephropathy is known and likely to start at a young age. Renal biopsies of children and adolescents who had normal eGFR and no proteinuria had exhibited glomerular sclerosis and vascular lesions [6,7], and glomerular GL-3 have also been detected in fetuses [8]. Our patient had a more severe form of nephropathy where his a-galactosidase levels are 0% and overt proteinuria at an early age. This is explained by Mahmud et al. [9], where patients with a-galactosidase levels of less than 1% tend to be more severe. Those with enzyme levels detectable in the renal involvement are usually less severe and begin late at a mean age of 47 years.
To date, more than 900 mutations of a-galactosidase gene have been recorded in the human mutation database [10]. Most families have private mutations which may explain the variations in the clinical presentation of Fabry's disease. The variant both our patient and his family have is a rare heterogenous variant of c.610 T > C. To date, only 3 occurrences can be found in ClinVar with no detailed clinical information [11].
In a renal biopsy, a typical histopathological lesion is the diagnostic of Fabry disease. Here, Fabry's inclusions can be identified with PAS or Papanicolaou stain demonstrating vacuolated epithelial cells on light microscopy and Maltese cross pattern under polarized light or characteristic lamellar pattern on electron microscopy [9]. This is as shown in the renal biopsy of our patient which showed all the typical features.
The mainstay of treatment of FD is ERT, and its initiation is recommended in classically affected males and females as soon as early clinical signs of FD occurrence [12].
For the normal population as well as for FD patients, it is a known fact that kidney function decreases with age [2,3]. Nowak et al. [13] found that male FD patients showed a clear decline of kidney function (eGFR) of 3.07 mL/ min/1.73m 2 per year over time despite being on ERT. It has also been proposed that male FD patients can pass through several CKD stages ending up with end-stage renal disease within 15 years after the initiation of ERT later in the stage. They also observed that the late initiation of ERT does not show a clear treatment-related benefit on the development of Fabry nephropathy [13]. Our patient was initiated ERT at the age after 35 which is considered late stage and already had significant proteinuria. There are no changes seen in the proteinuria over the years. He had rapid declination in renal function compared to the normal population about 4.3 mL/ min/1.73m 2 per year but slower declination compared to untreated male FD. Schiffmann et al. [14] reported that for untreated male FD with substantial proteinuria, the rate of renal declination is 6.9 mL/min/1.73 m 2 per year [14] while Branton et al. [15] reported a declination rate of 12 mL/ min/1.73 m 2 per year.
On the other hand, a recent study has found that proteinuria seems to be associated with decreased effectiveness of ERT [16,17]. According to Nowak et al. [13], disease progression was accelerated if ERT patients already had a more severe albuminuria at baseline, similar to this case. This is supported by Wanner et al. [18] whose studies showed that patients with faster progression had significantly higher proteinuria and renal function and men declined more rapidly for those with increased urinary protein levels. However, studies suggest that maximal treatment effect in Fabry nephropathy can be achieved at an early stage with normal or almost normal kidney function [19,20]. This maximal treatment also proved to provide a better renal and cardiovascular  outcome [20]. ACEi/ARB therapy in conjunction with ERT can reduce proteinuria and stabilize renal function in Fabry patients [21]. Similarly, in this case, perindopril was started for this reason. In addition to that, another possibility for poor treatment response is the development of neutralizing antibodies to ERT. In a study conducted by Linthorst et al. [22], it was found that 69% of male FD developed Ig G antibodies to agalsidase alpha and beta within 6 months of treatment especially in a patient who does not express residual enzyme activity, similar to our patient. And it was also found that once neutralizing antibodies had developed, it is irreversible and would stay positive for over 10 years [23]. However, due to restricted local resources, the IgG antibody development towards agalsidase beta in the patient was not able to be confirmed. Furthermore, there is no alternative treatment which is currently available for classic male FD with a lack of enzyme activity.
Despite the progression of Fabry nephropathy, the treatment of ERT had not been stopped as it was not recommended to stop even in severe renal insufficiency (GFR < 45 mL/min/1.73 m 2 ) or those on dialysis or with cognitive decline. It was however carefully considered on an individual basis [12]. As once GFR has been compromised, the goal is reduction and stabilization in the rate of CKD progresses [24]. Furthermore, ERT can reduce the occurrence of major renal, cardiac, and cerebrovascular events. Further reported extrarenal benefits include, for example, a decrease in neuropathic pain, improvement of gastrointestinal symptoms, and reduction of left ventricular mass [4].

Conclusion
To conclude, Fabry disease is a rare disease with a wide spectrum of clinical manifestations which makes diagnosing even more difficult for clinicians. Thus, in cases where no apparent causes can be found, a high index of suspicion is the key. Proteinuria is the predominant factor in Fabry nephropathy predicting renal disease progression rate. Therefore, an early Fabry disease diagnosis could prevent kidney disease progression through the timely initiation of treatment which will help enhance the quality of life of the patient, as the disease progresses.

Learning Points
• Fabry disease is a rare disease with a wide spectrum of clinical manifestations. • A high index of suspicion in cases where no apparent causes can be found. • Early diagnosis is needed for timely initiation of ERT to enhance the quality of life of the patient.