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Abstract
Background/aims Fabry disease is an X linked lysosomal disorder associated with severe multiorgan failure and premature death. This study aims to determine the prevalence of ophthalmic manifestations in children with the condition and investigate the correlation with genotype and systemic disease severity.
Methods The records of 26 children from 18 pedigrees with Fabry disease undergoing regular ophthalmic and systemic examination were reviewed. All pedigrees underwent GLA gene sequencing to determine genotype. Correlations between ocular and systemic phenotype and genotype were investigated.
Results Corneal verticillata occurred in 50% of the children in this study (95% CI, 29% to 79%). Children with ophthalmic manifestations were more likely to have loss-of-function GLA mutations (p=0.003). Retinal vascular tortuosity was seen in seven children (27%), all of whom had systemic symptoms suggestive of autonomic neuropathy, such as diarrhoea and syncope. These symptoms seemed less prevalent in children without retinal vascular changes, although this did not reach statistical significance (p=0.134).
Conclusion Ophthalmic manifestations of Fabry disease are common even in young children with loss-of-function GLA gene mutations. Although the limited sample size possibly prevented statistical significance, systemic symptoms of autonomic neuropathy often coexist with retinal vascular changes and may share the same pathogenesis.
- Child
- eye diseases/diagnosis
- Fabry disease/complications
- Fabry disease/diagnosis
- Fabry disease/drug therapy
- Fabry disease/physiopathology
- genetics
- child health (paediatrics)
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- Child
- eye diseases/diagnosis
- Fabry disease/complications
- Fabry disease/diagnosis
- Fabry disease/drug therapy
- Fabry disease/physiopathology
- genetics
- child health (paediatrics)
Fabry disease (OMIM 301500) is an X linked, inherited lysosomal storage disorder associated with severe multiorgan dysfunction and premature death.1 2 Fabry disease is hemizygous in males and heterozygous in females, but both genders can be severely affected, although the disease is usually slower to progress and is more variable in females.2–6 The condition is rare, with an estimated incidence of up to 1 in 40 000 male live births.7 GLA gene mutations reduce the activity of α-galactosidase A, resulting in globotriaosylceramide deposition in a variety of cells, including those of the kidney, the autonomic and cardiovascular system and the cornea.1 2 8
Ophthalmologists are a key group in the identification and referral of patients with Fabry disease. Eye examinations are relatively simple and represent a non-invasive method for assisting in the clinical diagnosis of patients with potential Fabry disease.9 10 Ophthalmological manifestations of Fabry disease result from the progressive deposition of glycosphingolipids in various ocular structures, although these do not usually cause ocular symptoms or visual impairment.9 The most frequently reported eye abnormalities are corneal verticillata (corneal opacities), conjunctival and retinal vascular abnormalities (vessel dilatation and tortuosity) and lens opacities (figures 1 and 2).9 10 Ophthalmological signs are usually present in children before serious systemic symptoms develop.11
Slit-lamp photograph of corneal verticillata.
Fundus photograph of moderate retinal vascular tortuosity.
The relative rarity and variability of the condition make diagnosis difficult, and many patients have delayed diagnosis or misdiagnosis for years. In the Fabry Outcome Survey (FOS), of 366 patients in all age groups, the mean time between onset of symptoms and diagnosis was 13 years for men and 16 years for women.12 In children (<18 years), there was an approximate 3-year delay between symptom onset and diagnosis.11 Accurate and rapid diagnosis of Fabry disease, particularly in children, is urgently needed now that effective treatment with enzyme replacement therapy (ERT) is available. Replacement α-galactosidase A (agalsidase alfa, Replagal (Shire Human Genetic Therapies, Cambridge, MA, USA); agalsidase B, Fabrazyme (Genzyme Europe, Naarden, The Netherlands)) therapy has been demonstrated to clear tissue globotriaosylceramide and to improve clinical end points, including stabilising renal function, reducing pain, improving cardiac structure and function, improving gastrointestinal symptoms and stabilising mild-to-moderate hearing loss.13–17 It may now therefore be possible to halt and even reverse the progress of Fabry disease before irreversible organ damage occurs.
Symptoms of Fabry disease, particularly acroparaesthesiae (numbness, pain or tingling in the extremities) and altered temperature sensitivity, altered bowel habits and abdominal pain, together with angiokeratoma, hypohidrosis, lethargy, and ophthalmological and auditory signs, usually present in childhood (<10 years), with life-threatening renal, cardiac or neurological complications in adulthood.1 2 7 11 12 Resultant renal failure, cardiomyopathy and cerebrovascular disease lead to premature death, on average 15 years earlier in women and 20 years earlier in men compared with the general population.1 2 To extend these studies in children, we investigated the relationship between genotype, ophthalmic phenotype and the severity of the systemic manifestations in children with the diagnosis of Fabry disease who are attending our centre. The aim was to assess whether ocular involvement is associated with a more severe systemic phenotype in affected children and whether this is related to genotype.
Materials and methods
The Paediatric Metabolic Unit of Cambridge University Hospitals NHS Foundation Trust (Addenbrooke's Hospital) holds a database of children with Fabry disease seen in the department. All pedigrees are genotyped by GLA gene sequencing, and the children have annual ophthalmic and biannual systemic examinations.
We analysed the first recorded ophthalmic examination and clinical findings for eight different systems for children with Fabry disease undergoing their biannual review.
The ophthalmic examination included visual acuity assessment, refraction and slit-lamp examination for conjunctival and retinal vascular tortuosity, corneal haze/verticillata and lens opacities. Anterior-segment and retinal photographic examinations were performed. Retinal vascular tortuosity was assessed by an experienced ophthalmologist (LEA) studying the calibre and directness of path of vessels by digital retinal photographs.
Systemic examination included a general assessment performed by an experienced metabolic paediatrician (UR), with specific questioning regarding symptoms and full physical examination. Radiological evaluation of cardiac, renal and neurological function, and audiometry were performed annually at the same centre by experienced personnel.
ERT is considered by the paediatric metabolic team if a child has uncontrolled pain leading to a need to alter lifestyle or pain that interferes with quality of life and has one or more of the following manifestations: severe asthenia; lethargy; gastroenterological symptoms such as pain, vomiting or altered bowel habit; abnormal MRI findings; episodic vertigo; intraventricular conduction defects and/or poor growth that cannot be accounted for by another cause.18
Systemic phenotyping was determined by multisystem history, examination and laboratory results. Ocular and systemic phenotypes were correlated with genotype, gender, age, systemic manifestations of the disease and commencement of ERT.
Results
We reviewed data from 26 children from 18 pedigrees (12 hemizygous boys of a median age of 5 years and 14 heterozygous girls of a median age of 11 years (range, 1–15 years). Seven children (three boys and four girls; median age, 8 years; range, 3–15 years) were already receiving ERT at the time of the first ophthalmic examination.
Molecular genetic results
Thirteen different GLA gene mutations were identified (table 1). Loss-of-function mutations affected 17 children; mutations predicted to give residual enzymatic activity affected nine children.
GLA genotypes detected in patients with Fabry disease
Ophthalmic examination
Thirteen (50%) of the 26 children were found to have corneal verticillata, the youngest being a 2-year-old girl (95% CI, 29% to 79%). None had severe corneal manifestations, and of the seven children with moderate changes, six were heterozygous girls. The median age of the children with verticillata was 8.1 years (range, 2–15 years), while that of the group without verticillata was 10.9 years (range, 1–15 years).
Seven children (27%) had evidence of retinal vascular tortuosity, the youngest being 4 years of age. One child of 5 years of age had mild spoke cataracts, but no patient had conjunctival vascular tortuosity.
All seven children (four girls and three boys) with retinal vascular tortuosity had neurological (asthenia/temperature insensitivity/hypohidrosis/syncope) and gastrointestinal symptoms (nausea/vomiting/diarrhoea), and five had cardiac symptoms (chest pain and trivial valve disease including tricuspid and mitral regurgitation) and auditory signs (hearing impairment/tinnitus/vertigo; table 2). Of the other 19 children, 13 had gastrointestinal symptoms; 11, auditory problems; 8, neurological symptoms; and 10, cardiac symptoms (the Fisher exact test, p=0.134).
Systemic features in children with retinal vascular tortuosity
Systemic examination
The most frequent systemic manifestations of Fabry disease were gastrointestinal (n=20 patients), neurological (n=14), cardiac (n=15) and auditory (n=16) abnormalities. All other abnormalities were reported for less than five patients.
Ophthalmic manifestations were found in 76% of patients predicted to have no enzyme function and in only one patient with a genotype predicted to give some residual enzyme function (table 3; the Fisher exact test, p=0.003). However, patients predicted to have some residual enzyme function had a similar prevalence of neurological, gastrointestinal and auditory symptoms as those with loss-of-function mutations. Cardiac and renal symptoms were actually more common in the group with predicted residual enzyme function.
Comparison of frequency of systemic features with genotype groups
Discussion
Fabry disease is a rare condition, and in this context, the 26 children and adolescents included in the current study are a significant cohort of young patients. The data from the current study agree with and add to the literature on reported ophthalmological manifestations of Fabry disease.
The FOS demonstrated that the most common ocular manifestation of Fabry disease is corneal verticillata (occurring in approximately 70% of adult patients) and that its presence does not correlate with Fabry illness severity measured by disease progression, renal function and cardiac size.10 In our study, corneal verticillata were seen in 50% of children studied (95% CI, 29% to 79%), the youngest being a 2-year old heterozygous girl. The children with verticillata did not tend to be older than the group without corneal changes.
The FOS showed a prevalence of retinal vascular tortuosity of 49% in males and 22% in females and of Fabry cataract in 23% males and 10% females; these features are thought to become more common with age.10 11 Vessel tortuosity on its own is not diagnostic for Fabry disease but has been recognised as being predictive of a more severe illness.10 19 Retinal vascular tortuosity was present in 27% of the children in this study and was identified in a child of only 4 years of age. Whereas all the children who had evidence of retinal vascular tortuosity also had gastrointestinal and neurological symptoms, a minority of those without retinal vascular changes manifested these symptoms of autonomic neuropathy. This did not meet statistical significance (the Fisher exact test, p=0.134) in our study possibly because of the small sample size, but does hint of a possible association between these features.
The pathophysiology of retinal vascular dilatation and tortuosity in Fabry disease is not fully understood. Autonomic neuropathy has been implicated as the cause of diarrhoea, hypohidrosis and syncope seen in Fabry patients.20 Autonomic neuropathy secondary to diabetes has been reported to cause bulbar and retinal vascular dilatation and tortuosity, as has cervical sympathectomy, because of the detrimental effect on retinal vascular autoregulation.21–24 Retinal and bulbar conjunctival vessel dilatation and tortuosity are therefore likely to be a marker for autonomic neuropathy in Fabry patients.
Loss-of-function mutations affected approximately two-thirds of the patients in the present study, while mutations predicted to give residual enzymatic activity affected about one-third of the patients. Although ophthalmic findings were much more commonly associated with loss-of-function mutations (the Fisher exact test, p=0.003), the prevalence of cardiac and renal systemic manifestations was higher in genotypes with predicted residual enzymatic activity.
Although the absence of ophthalmic signs does not appear to correlate with milder systemic disease, those children with absent eye signs but known systemic manifestations of Fabry disease may be predicted to have a missense mutation causing residual enzyme activity rather than a loss-of-function mutation.
Ophthalmological examination including slit-lamp examination should be conducted in young patients with symptoms of Fabry disease (eg, neuropathic pain, diarrhoea, tinnitus, vertigo). Once other causes of corneal verticillata (such as long-term therapy with chloroquine or amiodarone) have been excluded, the presence of cornea verticillata is diagnostic of Fabry disease. The additional presence of retinal vascular tortuosity indicates that autonomic neuropathy is likely and that these patients may already have potentially severe systemic manifestations.
Serial ophthalmological examinations may also be useful in monitoring the response to ERT. Quantification of severity of corneal verticillata is currently highly subjective.10 The presence of retinal vascular dilatation and tortuosity was assessed subjectively in this study, and generally, this has been shown to be a reliable form of assessment.25 To date, there have been no large population studies determining the prevalence of retinal vascular dilatation and tortuosity in the normal population, although it is felt that these changes, even in childhood, may be a potential predictor for vascular disease in later life.25 The development of image analysis software such as Retinal Image multiScale Analysis may allow more accurate identification and monitoring of vascular changes during therapy.26
Conclusion
Ophthalmic signs of Fabry disease are common in even young children with loss-of-function GLA mutations. Children with conjunctival and retinal vascular dilatation and tortuosity are likely to have associated severe systemic disease, and this may be an indicator of autonomic neuropathy.
The ocular symptoms of Fabry disease are generally trivial, and few patients will visit an ophthalmologist spontaneously. It is important that optometrists and ophthalmologists are aware of the ocular features of Fabry disease and that paediatricians consider this diagnosis in children with neuropathic pain and gastrointestinal symptoms. Slit-lamp examination provides a simple, quick, inexpensive and painless screening test for children with symptoms suggestive of Fabry disease.
Early recognition of Fabry disease will ensure that therapies including ERT are considered at an early stage of disease progression, and we suggest that children with suspected Fabry disease are referred to a specialist centre for further evaluation and consideration of such treatment.
Acknowledgments
We thank Clare Taylor and Alison Hough, paediatric metabolic specialist nurses, for their help with tabulating the clinical data and Serena Nik-Zainal for her help with interpretation of the molecular genetic results.
References
Footnotes
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.