Case report : is low α-Gal enzyme activity sufficient to establish the diagnosis of Fabry disease ?

DOI: 10.5935/0101-2800.20170057 Doença de Fabry (DF) é uma doença de depósito lisossômico ligada ao cromossomo X, causada pela deficiência da enzima alfa-galactosidase A (α-Gal A) que leva ao acúmulo de glicoesfingolipídeos, principalmente globotriaosilceramide. Existem mais de 700 mutações conhecidas do gene da enzima, a maioria delas são causadoras de DF. Este relato de caso descreve sobre um paciente em hemodiálise com uma mutação do gene GLA rara e controversa, a D313Y. A investigação médica confirmou que D313Y é uma variante que leva à pseudodeficiência plasmática da enzima, mas não ocasiona DF. Assim, os sintomas clínicos que induziram a investigação da doença não devem ser atribuídos à DF e, portanto, não foi indicada a terapia de reposição enzimática. Resumo


IntRoductIon
Fabry disease is an X-linked lysosomal storage disease caused by alpha-galactosidase A (GLA) gene mutation, which leads to an alfa-galactosidase A enzyme (α-Gal A) deficiency and consequently accumulation of glycosphingolipids, mainly globotriaosilceramide.Globotriaosylceramide accumulates within lysosomes throughout the body, leading to complications on different organs and systems, such as central and peripheral nervous systems, the kidneys and the cardiovascular system. 1 More than 700 mutations in the GLA gene have been recognized. 2Importantly, GLA mutations can also be non-pathogenic.
Classical manifestations of Fabry disease begin on life's first decade, which comprise neuropathic pain, hypohidrosis, angiokeratomas, cochleovestibular and gastrointestinal disorders.Usually, after the second decade of life, transient vascular ischemia and stroke, chronic kidney disease (CKD), manifested by proteinuria and/or reduced glomerular filtration rate, cornea verticillata, cardiomyopathy and arrhythmia may appear. 1 Late-onset phenotypes with predominance of the involvement of the heart or the kidneys have also been described. 3,4abry disease has been described in several ethnic groups with an estimated prevalence of 1:40,000 to 1:170,000 current smoker (40 packs/year); and stopped alcohol consumption 4 years before.He was taking the following medications: clonidine, atenolol, calcium carbonate, and erythropoietin.He had episodes of arrhythmia during hemodialysis session and discoid lupus diagnosis for 3 years, for which he has been using corticosteroid and chloroquine.
The presence of clinical manifestations (Table 1) of Fabry disease was further investigated.The electrocardiogram revealed sinus rhythm, left ventricular hypertrophy and subepicardial ischemia of inferior and lateral walls.The echocardiogram showed a moderate concentric hypertrophy of the left ventricle with preserved dimension and function.Cornea verticillata was not detected.Magnetic resonance imaging (MRI), indicated to investigate white matter lesions, was not performed due to the risk of nephrogenic fibrosis secondary to gadolinium exposure. 9les. 1 Taking into consideration that Fabry disease is rare and its clinical manifestations may be slight, particularly in the late onset subtypes, one should be aware that the true prevalence of Fabry disease has probably been underestimated.In agreement with this hypothesis, recent screening surveys in newborn reported an incidence of 1:3,100. 5Among the highrisk population, such as individuals with idiopathic left ventricular hypertrophy or those in renal replacement therapy, the prevalence seems to be higher. 17][8] The development of cheaper diagnostic tools, such as the dried blood spot on filter paper, has facilitated the screening of high-risk populations.This strategy may allow the identification of Fabry disease patients in renal replacement therapy centers, spreading the diagnosis to relatives in earlier stages.In the other hand, nephrologists will be challenged to confirm or refuse the clinical diagnosis of Fabry disease from a positive screening result in each tested patient.
Herein, in this case report, we describe a carrier of the D313Y mutation, identified by screening of Fabry disease in hemodialysis male patients.This mutation is considered controversial in the literature.The patient had clinical findings, such as left ventricular hypertrophy, arrhythmia and end-stage renal disease (ESRD), which could be attributed to Fabry disease.This diagnosis was not confirmed, though.This case report highlights the importance of careful evaluation of suspected cases of Fabry disease, particularly when controversial mutations, new mutations or mutations of unknown significance are detected, in order to avoid misdiagnosis and inadequate indication of enzyme replacement therapy (ERT).

cAse RepoRt
A 44-year-old man on hemodialysis for seven years was enrolled in a high risk population screening for Fabry disease in 2015.His α-Gal A enzyme activity in dried blood spot was 1.24 μmol/L/h (reference: > 2.2 μmol/L/h).Due to low enzymatic activity, genetic test was performed.The nonsense mutation p.D313Y in exon 6, in homozygosis, was detected.
Patient reported periorbital swelling and fatigue for 10 years and systemic hypertension for more than 20 years.He denied ischemic coronary artery disease or stroke.He had no family history of CKD.He was a Importantly, the patient was submitted to a kidney biopsy in other nephrology service, before starting hemodialysis.The kidney tissue was stained with hematoxylin and eosin, periodic acid-Schiff, Masson trichrome, and silver.It contained 8 glomerulae (5 sclerotic, 3 with hyalinosis of glomerular capillary).Tubules and intersticium presented signs of chronicity.

Severe arteriosclerosis and arteriolosclerosis were the
The iatrogenic form disappears after discontinuation of the drug, though. 13Interestingly, patients in use of chloroquine and amiodarone may develop lipidic inclusions in renal tissue similar to the those found in Fabry disease patients. 14he detection of low α-Gal A activity associated with high plasma or urinary levels of globotriaosylceramide or lyso-globotriaosylceramide and the identification of an affected family member with classical manifestations are criteria that establish the diagnosis of Fabry disease when doubt is present. 15Plasma levels of globotriaosylceramide or lyso-globotriaosylceramide could not be evaluated in our patient.
His daughters, the only family members with whom he had contact, are obligatory carriers of the mutation.They had no clinical manifestation.The demonstration of tissue globotriaosylceramide deposition is considered to be the gold standard for a definitive diagnosis of Fabry Disease. 15Our patient had been submitted to a kidney biopsy few months before starting renal replacement therapy.The microscopic findings by light microscopy were suggestive of hypertensive nephrosclerosis, without histological findings of Fabry nephropathy (Table 2). 14 few considerations regarding kidney biopsy in Fabry disease should be mentioned.First, histological findings may be overlooked if a biopsy is not examined most significant alterations detected in the vascular compartment.In conclusion, histopathologic findings were suggestive of hypertensive nephrosclerosis.No histologic changes of Fabry nephropathy, such as vacuolization of podocytes, were identified by light microscopy.
Regarding his family history, the patient had 2 daughters.The genetic analysis performed in one of them unveiled, as expected, the same mutation p.D313Y.The other daughter refused the genetic test.Both daughters had no clinical manifestations of Fabry disease.

dIscussIon
The patient presented the mutation p.D313Y, substitution of GAT for TAT in cDNA 937 nucleotide, in the GLA gene.This mutation causes a unique substitution of an aspartate for a tyrosine, in +313 position. 10This leads to the formation of unstable α-Gal A in plasma pH.This mutated enzyme preserves ~60% of its physiological activity in lysosome, whose pH is 4.6.This is called enzymatic pseudodeficiency.It has been demonstrated that carriers of D313Y mutation have a diminished α-Gal A activity in plasma while its intracellular activity remains preserved. 10hus, if the dosage of α-Gal A enzymatic activity in leukocytes, and not only in dried blood spot, could have been performed, it would have been normal.
Most clinical studies have supported the hypothesis that D313Y mutation is not pathogenic. 11yso-globotriaosylceramide, a substrate of globotriaosylceramide molecule, exerts a wellestablished role in Fabry disease pathogenicity, therefore considered a biomarker of disease severity and prognosis. 12Its plasmatic levels are increased in patients with mutations that are proven to be pathogenic, but not in D313Y carriers. 12Otherwise, it has been suggested an association between D313Y mutation and white matter lesions. 10he physical examination did not reveal any clinical sign of the disease, such as angiokeratoma and cornea verticillata.Importantly, the patient was using chloroquine, which can lead to the development of cornea verticillata, also described as a characteristic finding in Fabry disease and present in almost all heterozygous male 1 .Other drugs that may cause cornea verticillata include amiodarone and indomethacin. 13There is no difference between drugrelated and Fabry disease-related cornea verticillata.

Light microscopy
The glycosphingolipid inclusions are removed during tissue processing for paraffin embedding.Therefore, the cells, especially podocytes, parietal epitelial cells, and distal tubular epithelial cells, appear vacuolated.Hyalinelike material accumulates in the media of arteries and arterioles (Fabry arteriopathy) and sometimes in the mesangial regions.

Electron microscopy
Highly electron-dense multilamellar inclusions of glycosphingolipid (myelin figures made of concentric layers and zebra bodies, which have elongated striped appearance) are present in various cell types.The inclusions also stain darkly by toluidine blue on semithin sections.Abundant inclusions are present in podocytes, parietal epithelial cells, and distal tubular cells.Arteries and arterioles show inclusions in smooth muscle cells and hyaline-like material, consistent with Fabry arteriopathy.
by an experienced nephropatologist.Second, toluidine-blue stained is helpful to demonstrate cytoplasmic deposits.Finally, a tissue fragment for electron microscopy should always be obtained, even when this technique is not immediately available, it should be required for further investigation.
A complete investigation of Fabry disease could not be performed in the present case.Semi-thin section stained with toluidine-blue and electron microscopy, Cardiac and cerebral MRI, useful tools to detect myocardial fibrosis and white matter lesions, respectively, could not be performed.Nevertheless, based on literature review and on clinical and laboratory investigation, it was concluded that the patient does not have Fabry disease.Hence, ERT was not indicated.

conclusIon
In our patient, the D313Y mutation did not cause Fabry disease.The lack of clinical manifestations and particularly the absence of histological findings of Fabry nephropathy allowed us to exclude the diagnosis and, consequently, to not indicate ERT.The diagnosis of Fabry Disease should not be based only on the presence of low enzymatic activity.In this regard, in a recent screening among male hemodialysis patients in Bahia that enrolled 2583 patients, pathogenic GLA mutation was detected in 3 out of 72 patients with low enzyme activity, suggesting that diagnosis of Fabry Disease in males may be associated with a large number of false-positive cases (i.e., low specificity) if based only on enzymatic activity.Other important information that genotyping may provide is the type of the GLA mutation, since some misense mutations have been demonstrated to be amenable for treatment with pharmacologic chaperone. 16edical practice has embraced new helpful technologies during the last decades, such as genotyping.Nevertheless, the diagnosis should always be based on a detailed medical and family history as well as on physical examination.One should be aware that, beyond indicating an unnecessary treatment, an incorrect diagnosis of a hereditary disorder may impose to patients and their families an additional emotional burden, which will certainly have a negative impact in their sense of well-being and quality of life.