[Fabry disease. Clinical and genetic aspects. Therapeutic perspectives]

Analysis of globotriaosylceramide (Gb3) isoforms/analogs in unfractionated leukocytes, B lymphocytes and monocytes from Fabry patients using ultra-high performance liquid chromatography/tandem mass spectrometry

Fabry disease is an X-linked lysosomal storage disorder with marked variability in the phenotype and genotype. Glycosphingolipids such as globotriaosylceramide (Gb₃) isoforms/analogs, globotriaosylsphingosine (lyso-Gb₃) and analogs, and galabiosylceramide (Ga₂) isoforms/analogs may accumulate in biological fluids and different organs. The aims of this study were to: 1) develop/validate a novel UHPLC-MS/MS method for relative quantitation of Gb₃ in leukocytes (unfractionated white blood cells), B lymphocytes and monocytes; 2) evaluate these biomarkers in a cohort of Fabry patients and healthy controls; and 3) assess correlations between these biomarkers, treatment and genotype. Whole blood, plasma and urine samples from 21 Fabry patients and 20 healthy controls were analyzed. Samples were purified by liquid-liquid extraction and analyzed by UHPLC-MS/MS in positive electrospray ionization. Methylated Gb₃ isoforms were detected, showing that a methylation process occurs at the cellular level. Our results show that there were no significant differences in the distribution of the different Gb₃ isoforms/analogs in blood cells between Fabry patients and healthy controls. In leukocyte, Gb₃[(d18:1)(C14:0)], Gb₃[(d18:1)(C16:0)], Gb₃ [(d18:1)(C16:0)]Me, Gb₃ [(d18:1)(C16:1)], Gb₃ [(d18:1)(C18:0)], Gb₃ [(d18:1)(C18:1)], Gb₃ [(d18:1)(C20:1)], Gb₃ [(d18:1)(C24:2)], Gb₃ [(d18:1)(C26:1)] and total Gb₃ allowed good discrimination between male Fabry patients and male controls, patients having higher biomarker levels than controls. Regarding B lymphocytes and monocytes, the same tendency was observed without reaching statistical significance. A positive concordance between mutation types and biomarker levels in white blood cells was established. Our results might provide a deeper mechanistic comprehension of the underlying biochemical processes of Gb₃ biomarkers in white blood cells of Fabry patients.

Fabry's disease: an example of cardiorenal syndrome type 5

Cardiorenal syndrome type 5 (CRS-5) includes conditions where there is a simultaneous involvement of the heart and kidney from a systemic disorder. This is a bilateral organ cross talk. Fabry's disease (FD) is a devastating progressive inborn error of metabolism with lysosomal glycosphingolipid deposition in variety of cell types, capillary endothelial cells, renal, cardiac and nerve cells. Basic effect is absent or deficient activity of lysosomal exoglycohydrolase a-galactosidase A. Renal involvement consists of proteinuria, isosthenuria, altered tubular function, presenting in second or third decade leading to azotemia and end-stage renal disease in third to fifth decade mainly due to irreversible changes to glomerular, tubular and vascular structures, especially highlighted by podocytes foot process effacement. Cardiac involvement consists of left ventricular hypertrophy, right ventricular hypertrophy, arrhythmias (sinus node and conduction system impairment), diastolic dysfunction, myocardial ischemia, infarction, transmural replacement fibrosis, congestive heart failure and cardiac death. Management of FD is based on enzymatic replacement therapy and control of renal (with anti-proteinuric agents such as angiotensin-converting enzyme inhibitors-and/or angiotensin II receptor blockers), brain (coated aspirin, clopidogrel and statin to prevent strokes) and heart complications (calcium channel blockers for ischemic cardiomyopathy, warfarin and amiodarone or cardioverter device for arrhythmias).

Fabry disease

Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A activity. FD is pan-ethnic and the reported annual incidence of 1 in 100,000 may underestimate the true prevalence of the disease. Classically affected hemizygous males, with no residual α-galactosidase A activity may display all the characteristic neurological (pain), cutaneous (angiokeratoma), renal (proteinuria, kidney failure), cardiovascular (cardiomyopathy, arrhythmia), cochleo-vestibular and cerebrovascular (transient ischemic attacks, strokes) signs of the disease while heterozygous females have symptoms ranging from very mild to severe. Deficient activity of lysosomal α-galactosidase A results in progressive accumulation of globotriaosylceramide within lysosomes, believed to trigger a cascade of cellular events. Demonstration of marked α-galactosidase A deficiency is the definitive method for the diagnosis of hemizygous males. Enzyme analysis may occasionnally help to detect heterozygotes but is often inconclusive due to random X-chromosomal inactivation so that molecular testing (genotyping) of females is mandatory. In childhood, other possible causes of pain such as rheumatoid arthritis and 'growing pains' must be ruled out. In adulthood, multiple sclerosis is sometimes considered. Prenatal diagnosis, available by determination of enzyme activity or DNA testing in chorionic villi or cultured amniotic cells is, for ethical reasons, only considered in male fetuses. Pre-implantation diagnosis is possible. The existence of atypical variants and the availability of a specific therapy singularly complicate genetic counseling. A disease-specific therapeutic option - enzyme replacement therapy using recombinant human α-galactosidase A - has been recently introduced and its long term outcome is currently still being investigated. Conventional management consists of pain relief with analgesic drugs, nephroprotection (angiotensin converting enzyme inhibitors and angiotensin receptors blockers) and antiarrhythmic agents, whereas dialysis or renal transplantation are available for patients experiencing end-stage renal failure. With age, progressive damage to vital organ systems develops and at some point, organs may start to fail in functioning. End-stage renal disease and life-threatening cardiovascular or cerebrovascular complications limit life-expectancy of untreated males and females with reductions of 20 and 10 years, respectively, as compared to the general population. While there is increasing evidence that long-term enzyme therapy can halt disease progression, the importance of adjunctive therapies should be emphasized and the possibility of developing an oral therapy drives research forward into active site specific chaperones.

Aspects pédiatriques de la maladie de Fabry

Fabry's disease is a rare X-linked inborn error of glycosphingolipid metabolism characterised by an abnormal lipid storage due to a defect of lysozomal alphagalactosidase. The consequence is a storage of glycosphingolipides in all tissues. This storage in vessels's endothelial cells is responsible, in males, for severe ischemic lesions leading to progressive kidney failure, cardiac and cerebral dysfunctions. Similarly, it involves ocular tissues, mainly the cornea, the conjunctiva and the lens. The corneal storage, known as cornea verticillata, is a clinical marker easy to recognize by slit lamp examination of the affected males and carrier females. The enzymatic activity of alphagalactosidase is reduced in tears. Characteristic lamellar bodies can be observed by electron microscopy study of a conjunctival biopsy. Until recently, treatment was limited to symptomatic management of pain, and end-stage complications of renal failure, cardiac or brain disease. Recent studies have demonstrated that enzyme replacement therapy by genetic engineering is now shown to be promising for affected patients.

Hearing loss in a family affected by Fabry disease

Fabry disease is an inborn error of metabolism due to deficient activity of the lysosomal enzyme alpha-galactosidase A. The enzyme defect leads to the systemic accumulation of neutral glycosphingolipids in tissues. Otological manifestations consist of hearing loss and mild vestibular disorders. In this report we describe a family of five members affected by Fabry disease with four subjects showing inner ear involvement.

[Adult onset hereditary leukoencephalopathies]

In clinical practice, the term "genetic leukoencephalopathy" refers to a group of genetic diseases whose common point is to give an aspect of diffuse leukoencephalopathy on MRI. With progress in diagnostic techniques including radiology, biochemistry or genetics, a large number of hereditary diseases causing leukoencephalopathy have been identified. Although generally beginning in childhood, these diseases often have more insidious clinical forms which can begin in adulthood. These forms remain poorly known. Some are accessible to treatment so their diagnosis appears essential. The diagnostic steps must be guided by clinical examination (neurological, ophthalmological and systemic), electromyography and MRI. The purpose of this review is to propose a classification of the genetic leukoencephalopathies and to give a progress report applicable in neurological practice.

Fabry disease: a review

Fabry disease is an inherited deficiency of the lysosomal hydrolase alpha-galactosidase A (alpha GalA) due to mutations in the Gal gene at Xq22. The result is intralysosomal accumulation of glycosphingolipids. In males who carry the mutation (1/40,000), severe multisystem disease develops in childhood or adolescence. Attacks of acute pain lasting a few minutes to a few days occur in the hands and feet, joints, muscles, and abdomen, sometimes with a fever. Highly suggestive skin lesions called angiokeratomas develop, as well as cornea verticillata characterized by corneal deposits without visual impairment. Stroke, seizures, heart disorders (conduction disturbances, valve disease, and left heart failure) and kidney disorders (proteinuria and chronic renal failure) develop in the third or fourth decade of life. Women who are heterozygous for the Gal gene can transmit the disease to their sons but are usually free of symptoms, although many have cornea verticillata. However, they may have moderate or severe disease related to uneven chromosome X inactivation. Late-onset variants with predominant neurological, cardiac, or renal manifestations have been described. The diagnosis is difficult when the family history is negative for Fabry disease. Tests on plasma and leukocytes show very low levels of alpha GalA activity in affected men, confirming the diagnosis. The Gal gene mutation should be looked for to detect heterozygous women. Symptomatic treatments include analgesics, antihypertensives, antiplatelet agents or anticoagulants to treat ischemic events, and hemodialysis or kidney transplantation to treat chronic renal failure. The recent introduction of enzyme replacement therapy with recombinant agalsidase alpha or beta has been a major breakthrough in the treatment of Fabry disease. Enzyme replacement therapy relieves the pain and decreases the risk of complications. The safety profile is good. Given the high cost of agalsidase therapy (about 160,000 euro/year/patient) and the low incidence of Fabry disease, patients should be referred to highly specialized centers (see addresses on the France Orphanet web site).

[Contribution of genetics to knowledge and management of hereditary kidney diseases progressing to renal failure]

Genes of most of the hereditary renal diseases progressing to renal insufficiency are now identified. In the first part of this paper we describe their multi-faceted genetics. Genetic heterogeneity has been demonstrated in many of these diseases, such as Alport's syndrome and nephronophtisis. In some of them an allelic heterogeneity is present as in the X-linked form of Alport's syndrome (more than 300 different mutations have been described along the COL4A5 gene). Besides these classical mendelian diseases, mendelian subentities have been isolated within common diseases such as cortico-resistant nephrosis. Many diseases also demonstrate a variability of their phenotype resulting from allelic and/or genetic heterogeneity, or from modifier genes. In the second part of the paper we discuss the consequences of this explosion of knowledge with respect to epidemiology, genetic diagnosis, prenatal diagnosis and treatment.

Co-occurrence and contribution of Fabry disease and Klippel-Trénaunay-Weber syndrome to a patient with atypical skin lesions

Fabry disease (FD) is an X-linked recessive inborn error of glycosphingolipid metabolism. Among clinical symptoms, maculopapular skin lesions, known as angiokeratoma, most often appear on the lower abdomen, scrotum, and thighs, with a tendency toward bilateral symmetry. A 30-year-old male patient was referred to us for evaluation of a complex vascular and cutaneous malformation. Skin examination showed numerous angiokeratoma, which had developed only on the right part of the body, with a sharp delineation in the midline of the trunk. The diagnosis of FD was confirmed by demonstration of a decreased alpha-galactosidase A activity, and the patient was shown to be hemizygote for a missense mutation (R342Q) in the alpha-galactosidase A gene (GLA). This mutation was also demonstrated in DNA extracted from fibroblast cultures established from both affected and unaffected skin areas, thus excluding the hypothesis of somatic mosaicism or revertant mosaicism. Interestingly, the diagnosis of Klippel-Trénaunay-Weber syndrome (KTWS) was also made, through clinical and radiological investigations. This is the first report on the association between FD and KTWS. Karyotype analysis was normal. It is likely that the mixed vascular malformations of KTWS affecting capillary and venous systems have contributed to the unusual angiokeratoma distribution pattern observed in the patient.

Identification of fifteen novel mutations and genotype-phenotype relationship in Fabry disease

Fabry disease is an X-linked recessive disorder caused by a deficiency in the lysosomal enzyme alpha-galactosidase A, which results in a progressive multisystem disease. Most families have private mutations and no general correlation between genotype and disease manifestations has been described to date. Forty-nine patients (47 males and 2 females) from 36 affected families were selected for the study. Their evaluation included clinical examination, identification of alpha-galactosidase A gene mutations and residual enzymatic activity. For mutation detection, each exon with flanking intronic sequences was amplified by polymerase chain reaction (PCR) from the patient's genomic DNA and sequenced. Analysis of the resulting sequences was conducted to identify structural defects in the gene. Each of the Fabry patients carried a mutation in the alpha-galactosidase A gene. Fifteen mutations were novel. They included missense mutations (M51K, Y123M, G261D), nonsense point mutations (E251X) and small insertions or deletions creating a premature translational termination signal (P6X, D93X, W162X, K240X, H302X, I303X, L403X, S345X, G375X, F396X). Residual alpha-galactosidase A activity was significantly lower in patients with neuropathic pain (p=0.01) and in patients with mutations leading to a nonconservative amino acid change (p=0.04). Our findings emphasize the wide variety of genetic mechanisms leading to Fabry disease. A significant genotype-phenotype relationship was found.