Fabry disease encompasses a spectrum of phenotypes ranging from the severe classic phenotype to atypical late-onset forms. The late-onset forms are more common than the classic phenotype. However, in registries and publications individuals with the classic phenotype are overrepresented.
Individuals with atypical Fabry disease present later in life and are underdiagnosed [Germain 2010]. Significant diagnostic delays are reported in the Fabry Outcome Survey (FOS) [Mehta et al 2004]; they are particularly common in females [Ellaway 2015] and may lead to avoidable complications [Reisin et al 2017].
The FOS and the Fabry Registry, multicenter international initiatives designed to examine the natural history of Fabry disease and the effects of enzyme replacement therapy (ERT), are an important source of long-term data on the disease [Giugliani et al 2016, Ortiz et al 2016, Ramaswami et al 2019a, Wanner et al 2020].
Classic Fabry Disease
This is usually seen in hemizygous males with <1% alpha-galactosidase A (α-Gal A) enzyme activity but may occasionally be seen in heterozygous females. Onset of symptoms usually occurs in childhood or adolescence with the appearance of angiokeratomas, periodic crises of severe pain in the extremities (acroparesthesia), hypohidrosis, and the characteristic corneal and lenticular opacities. Although proteinuria may be detected early, renal insufficiency usually occurs in the third to fifth decade of life. Death occurs from complications of kidney disease, cardiac involvement, and/or cerebrovascular disease.
Angiokeratomas are an early manifestation of Fabry disease, typically seen in children and young adolescents [Luna et al 2016]. They appear as clusters of punctate, dark red to blue-black angiectases in the superficial layers of the skin. The lesions may be flat or slightly raised and do not blanch with pressure. Slight hyperkeratosis is notable in larger lesions.
The clusters of lesions are most dense between the umbilicus and the knees; they most commonly involve the hips, back, thighs, buttocks, penis, and scrotum, and tend to be bilaterally symmetric. The oral mucosa, conjunctiva, and other mucosal areas are commonly involved. Wide variation in the distribution pattern and density of the lesions may occur. Examination of the skin, especially the scrotum and umbilicus, may reveal the presence of isolated lesions. Data from 714 affected individuals (345 males, 369 females) in the FOS [Orteu et al 2007] suggest that they are present in 66% of males (36% of females).
The number and size of these cutaneous vascular lesions progressively increase with age. The presence of angiokeratomas correlated with the severity of the systemic disease manifestations [Zampetti et al 2012].
Acroparesthesia occurs as episodic crises of agonizing, burning pain in the distal extremities that most often begin in childhood or early adolescence and signal clinical onset of the disease [Burand & Stucky 2021]. These crises last from minutes to several days and are usually triggered by exercise, fatigue, emotional stress, or rapid changes in temperature and humidity. Often the pain radiates to the proximal extremities and other parts of the body. Attacks of abdominal or flank pain may simulate appendicitis or renal colic.
The crises usually decrease in frequency and severity with increasing age; however, in some affected individuals, the frequency increases and the pain can be so excruciating and incapacitating that the individual may contemplate suicide.
Nerve conduction studies show evidence of a small fire neuropathy [Biegstraaten et al 2012] affecting small myelinated and unmyelinated neurons [Soliman et al 2016].
Hypohidrosis or anhidrosis is an early and almost constant finding. Hyperhidrosis also occurs; in the FOS it was seen in 12% of females and 6.4% of males [Lidove et al 2006].
Cornea verticillata, the characteristic corneal opacity that is observed only by slit-lamp microscopy, is found in affected males and most heterozygous females. The earliest corneal lesion is a diffuse haziness in the subepithelial layer. With time, the opacities appear as whorled streaks extending from a central vortex to the periphery of the cornea. The whorl-like opacities, typically inferior and cream colored, range from white to golden brown and may be very faint [Nguyen et al 2005]. In the FOS, cornea verticillata was present in 77% of females and 73% of males undergoing detailed ophthalmologic examination [Sodi et al 2007].
Lenticular changes are present in approximately 30% of affected males and include a granular anterior capsular or subcapsular deposit and a unique, possibly pathognomonic lenticular opacity (the "Fabry cataract"). The cataracts, which are best observed through a dilated pupil by slit-lamp examination using retroillumination, are whitish, spoke-like deposits of fine granular material on or near the posterior lens capsule. These lines usually radiate from the central part of the posterior cortex. The corneal and lenticular opacities do not interfere with visual acuity.
Other ocular features. Aneurysmal dilatation and tortuosity of conjunctival and retinal vessels also occur [Sivley et al 2018]; while not specific for Fabry disease, vessel tortuosity is observed more frequently in individuals with a higher disease severity score [Sodi et al 2007, Allen et al 2010]. Data from the FOS demonstrates that the ocular changes correlate well with overall disease severity and with genotype [Pitz et al 2015]. Ocular abnormalities, especially microaneurysms and posterior and anterior cataracts, persist and progress despite treatment with ERT [Michaud 2019].
Cardiac disease is present in most males with the classic phenotype by middle age and is the major cause of morbidity and mortality [Azevedo et al 2021, Pieroni et al 2021, Vardarli et al 2021].
Mitral insufficiency may be present in childhood or adolescence. Left ventricular enlargement and conduction abnormalities are early findings. Left ventricular hypertrophy (LVH), often associated with hypertrophy of the interventricular septum and appearing similar to hypertrophic cardiomyopathy (HCM), is progressive and occurs earlier in males than females [Kampmann et al 2005]. EKG changes including ST segment changes, T-wave inversion, and dysrhythmias such as a short PR interval and intermittent supraventricular tachycardias may be caused by infiltration of the conduction system. Echocardiography demonstrates an increased thickness of the interventricular septum and the left ventricular posterior wall [Yeung et al 2018]. Magnetic resonance studies using gadolinium demonstrated late enhancement areas, corresponding to myocardial fibrosis and associated with decreased regional functioning as assessed by strain and strain-rate imaging [Weidemann et al 2005]. T1 mapping illustrates intramural fat deposition and posterior wall fibrosis [Sado et al 2013, Augusto et al 2021] which occurs prior to LVH. It has been hypothesized that a pre-storage myocardial phenotype might occur prior to T1 lowering with microvascular dysfunction, impaired global longitudinal strain, and altered atrial depolarization and ventricular repolarization intervals [Augusto et al 2021].
Among 714 predominantly adult individuals in the FOS [Linhart et al 2007], angina, palpitations/arrhythmia, and exertional dyspnea were found in 23%-27% of males and 22%-25% of females. Hypertension, angina pectoris, myocardial ischemia and infarction, congestive heart failure, and severe mitral regurgitation are late signs. Hypertension was found in more than 50% of males and more than 40% of females in the FOS [Kleinert et al 2006].
Cerebrovascular manifestations result primarily from multifocal small vessel involvement and may include thrombosis, transient ischemic attacks (TIA), basilar artery ischemia and aneurysm, seizures, hemiplegia, hemianesthesia, aphasia, labyrinthine disorders, or frank cerebral hemorrhage [Burlina & Politei 2016]. Individuals with Fabry disease had increased basilar artery mean diameter and basilar artery linear length compared with controls [Fellgiebel et al 2011, Manara et al 2017]. White matter lesions are frequently found on MRI of individuals with Fabry; age and prior stroke independently predicted the burden of white matter hyperintensities [Rost et al 2016, Körver et al 2020b].
Renal involvement. Progressive glycosphingolipid accumulation in the kidney interferes with renal function, resulting in azotemia and renal insufficiency.
During childhood and adolescence, protein, casts, red cells, and birefringent lipid globules with characteristic "Maltese crosses" can be observed in the urinary sediment. Proteinuria, isosthenuria, and a gradual deterioration of tubular reabsorption, secretion, and excretion occur with advancing age. Polyuria and a syndrome similar to vasopressin-resistant diabetes insipidus occasionally develop.
Gradual deterioration of renal function and the development of azotemia occur in the third to fifth decade of life in approximately 50% of males with classic Fabry disease [Branton et al 2002], rising to almost 90% by the sixth decade; although end-stage kidney disease (ESKD) has been reported in the second decade. Death most often results from ESKD unless chronic hemodialysis or kidney transplantation is undertaken. The mean age at death of males not treated for ESKD is 41 years, but occasionally an untreated male with the classic phenotype survives into the seventh decade.
Renal sinus and parapelvic cysts are seen in up to half of individuals with Fabry disease, compared to fewer than 10% of controls [Ries et al 2004].
Other clinical features. In addition to the major clinical features described above, males and females with the classic phenotype may have gastrointestinal, auditory, pulmonary, and other manifestations.
Gastrointestinal. Glycosphingolipid deposition in intestinal small vessels and in the autonomic ganglia of the bowel may cause episodic diarrhea, nausea, vomiting, bloating, cramping abdominal pain, and/or intestinal malabsorption [
Hoffmann et al 2007,
Politei et al 2016]. Symptoms resembling irritable bowel syndrome are reported in nearly 20% of individuals in the Fabry Registry [
Eng et al 2007]. Achalasia and jejunal diverticulosis, which may lead to perforation of the small bowel, have been described. Radiographic studies may reveal thickened, edematous colonic folds, mild dilatation of the small bowel, a granular-appearing ileum, and the loss of haustral markings throughout the colon.
Pulmonary. Several affected individuals have had pulmonary involvement, manifest clinically as chronic bronchitis, wheezing, or dyspnea. Primary pulmonary involvement has been reported in the absence of cardiac or renal disease. Pulmonary function studies may show an obstructive component which has been demonstrated to stabilize with ERT [
Svensson et al 2015,
Odler et al 2017,
Franzen et al 2018].
Vascular. Pitting edema of the lower extremities may be present in adulthood in the absence of hypoproteinemia, varices, or other clinically significant vascular disease. Although the pitting edema is initially reversible, progressive glycosphingolipid deposition in the lymphatic vessels and lymph nodes results in irreversible lymphedema requiring treatment with compression hosiery. Varicosities, hemorrhoids, and priapism have also been reported.
Cranial nerve VIII involvement. High-frequency hearing loss, tinnitus, and vestibular disturbance with dizziness have been reported [
Köping et al 2018]. Some studies indicate auditory involvement (including females and otherwise asymptomatic individuals) in up to 60% of individuals with Fabry disease [
Eyermann et al 2019].
Psychological. Symptoms of depression have been reported in up to 60% of individuals with Fabry disease and appear to be unrelated to structural brain alterations [
Schermuly et al 2011]. Anxiety, severe fatigue, and other psychosocial manifestations lead to decreased quality of life in many affected individuals [
Ali et al 2018,
Körver et al 2020a].
Fabry disease in children. Males generally present with the classic phenotype from age three to five years. Abdominal pain, acroparesthesia, hearing loss, cataract, skin rash, and fatigue are common features [Ramaswami et al 2006, Germain et al 2019b].
Heterozygous Females
The clinical manifestations in heterozygous females range from asymptomatic throughout a normal life span to as severe as affected males. Variation in clinical manifestations is attributed to random X-chromosome inactivation [Deegan et al 2006]. More severely affected females are more likely to express the X chromosome with the GLA pathogenic variant in affected organs [Echevarria et al 2016].
Most heterozygous females from families in which affected males have the classic phenotype have a milder clinical course and better prognosis than affected males.
Mild manifestations include the characteristic cornea verticillata (70%-90%) and lenticular opacities that do not impair vision; acroparesthesia (50%-90%); angiokeratomas (10%-50%) that are usually isolated or sparse; hypohidrosis; and chronic abdominal pain.
With advancing age, heterozygotes may develop mild-to-moderate LVH and valvular disease. More serious manifestations include significant LVH, cardiomegaly, myocardial ischemia, infarction, and cardiac arrhythmias [Deegan et al 2006, Wilcox et al 2008, Lenders et al 2016a].
The occurrence of cerebrovascular disease including transient ischemic attacks and cerebrovascular accidents is consistent with the microvascular pathology of the disease [MacDermot et al 2001].
Renal findings in heterozygotes include isosthenuria; the presence of erythrocytes, leukocytes, and granular and hyaline casts in the urinary sediment; and proteinuria. According to the United States and European dialysis and transplantation registries, approximately 10% of heterozygotes develop kidney failure requiring dialysis or transplantation.
Excessive guilt, fatigue, occupational difficulty, suicidal ideation, and depression have been noted in heterozygotes [Sadek et al 2004].