This test analyzes α-galactosidase (GLA), the only known gene associated with Fabry disease. Testing should be considered for any individual with a clinical diagnosis of Fabry disease, a suspected clinical diagnosis of Fabry disease, or a family history of Fabry disease. On average, five family members are diagnosed with Fabry disease for every proband identified.
Molecular analysis of GLA is the only reliable way of diagnosing heterozygous females. Enzymatic studies of α-galactosidase in females who are obligate carriers or manifesting heterozygotes are often inconclusive due to X-inactivation. Heterozygous females may have α-galactosidase levels within the normal range.
Fabry disease is a rare, complex lysosomal storage disease with multisystemic involvement due to the progressive accumulation of globotriaosylceramide (GL-3) in the vascular endothelium. There is a phenotypic spectrum ranging from the severe, classic phenotype, to an attenuated phenotype, to atypical cardiac or renal variants.
Heterozygous females—Females heterozygous for a GLA pathogenic variant may remain clinically asymptomatic, present with an attenuated form of the disease, or manifest the full clinical spectrum of symptoms observed in males with classic Fabry disease.
Cardiac variant—This phenotype generally presents in males with greater than 1% enzymatic activity. Cardiomyopathy develops in the sixth to eighth decade of life and is characterized by left ventricular hypertrophy, hypertrophy of the interventricular septum, mitral valve insufficiency, and/or conduction abnormalities. Proteinuria may also be a feature, but end stage renal disease is typically absent.
Renal variant—This variant presents in males with greater than 1% enzymatic activity and has been diagnosed in Japanese patients with end stage renal disease and a prior diagnosis of chronic glomerulonephritis. Other symptoms of classic Fabry disease are generally absent, although moderate-to-severe left ventricular hypertrophy acroparesthesias and hypohidrosis have also been reported with the cardiac variant.
The classic phenotype in hemizygous males is the most commonly reported. Symptom onset generally occurs in childhood or adolescence, with the median reported age of 6 years in males and 9 years in females. The first detectable symptoms are usually acroparesthesias, angiokeratomas, hypohidrosis, and/or ocular findings. Cardiac and cerebrovascular disease is usually evident by middle age. Chronic kidney disease is present by the third decade of life and progresses to end stage renal disease (ESRD) by the fifth decade of life unless treated by chronic hemodialysis or renal transplant. Untreated Fabry disease causes a significantly reduced lifespan; the major causes of morbidity and mortality are renal failure, cardiovascular disease, and stroke. Heterozygous females may remain asymptomatic with a normal lifespan, have an attenuated form of the disease, or manifest all features of the severe, classic disease. Milder, non-classical variants include a cardiac form that has isolated cardiac symptoms developing in both males and females during sixth to eighth decade of life, and a renal form that leads to end stage renal disease occurring in the same time frame as males with the classic form of the disease. Symptoms such as milder left ventricular hypertrophy, acroparesthesias, and hypohidrosis have also been reported in cases with the renal variant.
More than 99% of patients with a clinical diagnosis of Fabry disease have an identifiable pathogenic mutation in GLA.
Fabry disease is inherited in an X-linked pattern.
Almost 100% of males and up to 80% of females with identified pathogenic variants develop signs and/or symptoms of the disease. Phenotypic expression of disease is highly variable both within the same family and among different families, and there may be subclinical expression in affected females.
Males with less than 1% enzyme activity typically present with classic Fabry disease, while those with greater than 1% may present with the cardiac or renal variant.
Females harboring a Fabry mutation may also present with symptoms of Fabry disease ranging from the classic disease to subclinical findings.
Fabry disease is panethnic, with no racial or ethnic predilection.
Birth prevalence is estimated at 1 in 30 000–35 000 births. Incidence in the general population has been estimated at 1 in 40,000 classically affected males. As milder cardiac and renal variants are being identified, and as Fabry disease newborn screening programs are being launched, these figures are being challenged. Recent newborn screening studies have shown that Fabry disease prevalence may be as high as 1 in 1,250 in certain populations.
Testing for Fabry disease should be considered in males and females with any or all of the following clinical symptoms:
In the absence of these two factors, testing is indicated in patients with at least two of the features below:
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence in the transcript listed below. In addition, analysis covers the select non-coding variants specifically defined in the table below. Any variants that fall outside these regions are not analyzed. Any specific limitations in the analysis of these genes are also listed in the table below.
Based on validation study results, this assay achieves >99% analytical sensitivity and specificity for single nucleotide variants, insertions and deletions <15bp in length, and exon-level deletions and duplications. Invitae's methods also detect insertions and deletions larger than 15bp but smaller than a full exon but sensitivity for these may be marginally reduced. Invitae’s deletion/duplication analysis determines copy number at a single exon resolution at virtually all targeted exons. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. Certain types of variants, such as structural rearrangements (e.g. inversions, gene conversion events, translocations, etc.) or variants embedded in sequence with complex architecture (e.g. short tandem repeats or segmental duplications), may not be detected. Additionally, it may not be possible to fully resolve certain details about variants, such as mosaicism, phasing, or mapping ambiguity. Unless explicitly guaranteed, sequence changes in the promoter, non-coding exons, and other non-coding regions are not covered by this assay. Please consult the test definition on our website for details regarding regions or types of variants that are covered or excluded for this test. This report reflects the analysis of an extracted genomic DNA sample. In very rare cases, (circulating hematolymphoid neoplasm, bone marrow transplant, recent blood transfusion) the analyzed DNA may not represent the patient's constitutional genome.
|Gene||Transcript reference||Sequencing analysis||Deletion/Duplication analysis|
GLA: Analysis includes the intronic variant NM_000169.2:c.IVS4+919G>A.