Fabry Disease

Clinical meaning

Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the GLA gene encoding the enzyme alpha-galactosidase A (alpha-Gal A). Deficient or absent alpha-Gal A leads to progressive accumulation of globotriaosylceramide (Gb3, also called GL-3) and its deacylated form globotriaosylsphingosine (lyso-Gb3) within lysosomes of vascular endothelial cells, podocytes, cardiomyocytes, renal tubular cells, and dorsal root ganglia neurons. This progressive Gb3 deposition drives organ damage through several mechanisms: vascular endothelial dysfunction (promoting thrombosis and vasculopathy), cardiac hypertrophy (Gb3 infiltration of cardiomyocytes causes left ventricular hypertrophy mimicking hypertrophic cardiomyopathy), renal injury (podocyte and tubular cell damage causing progressive proteinuria and CKD leading to ESRD), and peripheral nervous system involvement (small fiber neuropathy causing the characteristic acroparesthesias). Because Fabry disease is X-linked, MALES (hemizygous) are classically more severely affected with earlier onset (childhood to adolescence), while FEMALES (heterozygous carriers) have variable severity due to random X-inactivation (lyonization) -- some carrier females are asymptomatic while others have severe disease. The classic male phenotype presents in childhood with episodic burning pain in the hands and feet (acroparesthesias), angiokeratomas (dark red papules clustered on the lower trunk, buttocks, and genitalia), corneal verticillata (whorl-like corneal opacities visible on slit-lamp exam), hypohidrosis (reduced sweating leading to heat intolerance), and GI symptoms (abdominal pain, diarrhea). Without treatment, progressive organ involvement leads to stroke, cardiac disease, and ESRD in the 4th-5th decades of life. The NP must maintain a high index of suspicion for Fabry disease in unexplained LVH, cryptogenic stroke in young adults, CKD of unknown etiology, and small fiber neuropathy.

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Diagnosis & workup

Diagnostics & workup: - Alpha-galactosidase A enzyme activity assay: the primary diagnostic test in MALES; measured in leukocytes or dried blood spots; classic males have <1% of normal activity; this test is NOT reliable in FEMALES because random X-inactivation can produce normal enzyme levels even in affected carriers -- females require genetic testing - GLA gene sequencing: definitive genetic diagnosis identifying the specific pathogenic mutation; essential for FEMALE diagnosis (enzyme levels are unreliable); also guides genotype-phenotype correlation and determines eligibility for specific therapies (e.g., migalastat requires an amenable mutation) - Plasma globotriaosylsphingosine (lyso-Gb3): elevated in Fabry patients and correlates with disease burden; useful biomarker for monitoring treatment response; more sensitive than Gb3 levels; elevated in both classic and late-onset variants - Cardiac MRI with gadolinium enhancement: identifies LVH pattern (concentric, symmetric), myocardial fibrosis (late gadolinium enhancement typically in the basal inferolateral wall -- characteristic distribution), and T1 mapping (low native T1 values from Gb3 deposition in the myocardium -- distinguishes Fabry cardiomyopathy from other causes of LVH) - Renal biopsy with electron microscopy: shows characteristic 'zebra bodies' (lamellar inclusions within podocytes) and Gb3 deposits in tubular cells, endothelial cells, and mesangial cells; performed when the diagnosis is uncertain or to assess degree of renal injury - Slit-lamp ophthalmologic examination: corneal verticillata (whorl-like corneal opacities from Gb3 deposition) present in >70% of classic males and many carrier females; finding is virtually pathognomonic for Fabry disease or amiodarone use (drug-induced pseudofabry)

Risk factors: - X-linked inheritance: males with a pathogenic GLA mutation will have Fabry disease; all daughters of an affected male will be obligate carriers; sons of an affected male are unaffected (Y chromosome from father); sons of a carrier female have a 50% chance of being affected - Family history of early stroke, unexplained renal failure, or hypertrophic cardiomyopathy: Fabry disease is frequently misdiagnosed; a family pedigree showing these complications in an X-linked pattern should prompt screening - Male sex with classic phenotype: hemizygous males typically have <1% residual alpha-Gal A activity and develop symptoms in childhood; classic presentation includes acroparesthesias, angiokeratomas, and corneal verticillata before age 10 - Female carriers with variable expressivity: due to random X-inactivation, some carrier females have near-normal enzyme levels and mild symptoms while others have severe disease approaching the male phenotype; females are frequently underdiagnosed - Late-onset variants: some GLA mutations cause the 'cardiac variant' or 'renal variant' with residual enzyme activity; these patients may not develop classic childhood symptoms but present in adulthood with isolated LVH or renal failure - Diagnostic delay: the average delay from symptom onset to Fabry diagnosis is 13-15 years for males and even longer for females; childhood acroparesthesias are frequently dismissed as 'growing pains' or diagnosed as rheumatic disease

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