Abstract
Background and Aims
Fabry disease (FD) is an X-linked hereditary disease. It results from mutations in the GLA gene, leading to deficient activity of the enzyme alpha-galactosidase A and progressive accumulation of undegraded glycosphingolipids in cell lysosomes. Enzyme replacement therapy improved the natural course of this disease, but an early diagnosis is crucial for a successful treatment.
Method
A screening study for GLA gene mutations was conducted for all patients under dialysis, from a single centre. All the probands with a detectable mutation were analysed individually. Data on the patient's family and personal pathological history were retrospectively collected, by consulting the clinical file.
Results
35 years-old female diagnosed with chronic proteinuric kidney disease in the postpartum period. Despite optimal medical treatment the disease progressed, and she started renal replacement therapy with peritoneal dialysis. Five years later she was enrolled in a pilot screening study for FD and the heterozygous mutation c.870G>C (p.Met290Ile; M290I) in exon 6 of the GLA gene was found. The proband didn’t meet the criteria for a definitive FD diagnosis, but she remained under follow-up at our nephrology metabolic diseases consultation, as the mutation was described as pathogenic and associated with a classic FD phenotype. Later that same year, reassessment exams revealed a worsening left ventricle mass index, a new ischemic cerebral lesion and a substantial increase in serum globotriaosylsphingosine (LysoGb3) levels. These clinical changes led to the decision to initiate enzyme replacement therapy.
Until now there are only a few descriptions of this genetic variant in the scientific literature. A Portuguese study analysed a total of 11 FD patients and described 2 patients with p.M290I mutation, without detectable Gb3 accumulation. Another study was designed to evaluate the genotype-phenotype relationship in 73 Chinese FD patients. Contrary to other reports, the p.M290I mutation was not associated to the classic FD phenotype. A Swiss investigation with a similar design analysed 69 FD patients during their routine annual examinations. M290I mutant enzyme was found in a 48-year-old heterozygous female with a classic FD phenotype but with a low serum LysoGb3. A Spanish newborn screening identified one male patient with FD and the p.M290I genetic variant but was unable to provide any information about the clinical expression of this mutation, since the diagnosis was made between the third and fifth days of life. The study describing the most patients carrying the M290I mutant enzyme is Brazilian and screened a total of 25,223 dialysis patients. Among 89 FD-positive patients, the p.M290I mutation was present in 22. However, the authors did not provide detailed information about the clinical manifestations or α-Gal A activity and LysoGb3 levels of these patients. Finally, a recent Portuguese screening of 150 hypertrophic cardiomyopathy patients found 25 patients with FD. Of these, one female carried the GLA gene variant p.M290I, with a non-detectable LysoGb3 plasma level.
Conclusion
We describe a case of FD due to a previously known but still poorly described GLA mutation, which offers strong evidence of its pathogenicity. To our knowledge, this is the first report of p.M290I mutation-associated disease activity evidenced by elevated levels of serum LysoGb3. Despite the absence of classic FD symptoms such as neuropathic pain, cornea verticillata and angiokeratoma, the presence of severe multiple organ evolvement, characterized by renal failure, cardiac disease and ischaemic stroke, strongly suggests a classic phenotype. Consequently, it is our opinion that the presence of a p.M290I GLA mutation should require a strict ongoing patient follow-up, as it may cause clinically significant disease.
The Management of Fabry Nephropathy