Metabolic pigmentary retinopathies: diagnosis and therapeutic attempts

Clinical and genetic spectrums of 413 North African families with inherited retinal dystrophies and optic neuropathies

Background

Inherited retinal dystrophies (IRD) and optic neuropathies (ION) are the two major causes world-wide of early visual impairment, frequently leading to legal blindness. These two groups of pathologies are highly heterogeneous and require combined clinical and molecular diagnoses to be securely identified. Exact epidemiological studies are lacking in North Africa, and genetic studies of IRD and ION individuals are often limited to case reports or to some families that migrated to the rest of the world. In order to improve the knowledge of their clinical and genetic spectrums in North Africa, we reviewed published data, to illustrate the most prevalent pathologies, genes and mutations encountered in this geographical region, extending from Morocco to Egypt, comprising 200 million inhabitants.

Main body

We compiled data from 413 families with IRD or ION together with their available molecular diagnosis. The proportion of IRD represents 82.8% of index cases, while ION accounted for 17.8%. Non-syndromic IRD were more frequent than syndromic ones, with photoreceptor alterations being the main cause of non-syndromic IRD, represented by retinitis pigmentosa, Leber congenital amaurosis, and cone-rod dystrophies, while ciliopathies constitute the major part of syndromic-IRD, in which the Usher and Bardet Biedl syndromes occupy 41.2% and 31.1%, respectively. We identified 71 ION families, 84.5% with a syndromic presentation, while surprisingly, non-syndromic ION are scarcely reported, with only 11 families with autosomal recessive optic atrophies related to OPA7 and OPA10 variants, or with the mitochondrial related Leber ION. Overall, consanguinity is a major cause of these diseases within North African countries, as 76.1% of IRD and 78.8% of ION investigated families were consanguineous, explaining the high rate of autosomal recessive inheritance pattern compared to the dominant one. In addition, we identified many founder mutations in small endogamous communities.

Short conclusion

As both IRD and ION diseases constitute a real public health burden, their under-diagnosis in North Africa due to the absence of physicians trained to the identification of inherited ophthalmologic presentations, together with the scarcity of tools for the molecular diagnosis represent major political, economic and health challenges for the future, to first establish accurate clinical diagnoses and then treat patients with the emergent therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02340-7.

Infantile Refsum disease in a young adult: case presentation and brief review

PURPOSE

To review and describe findings, pathophysiology, and management of infantile Refsum disease in a young adult, and to compare with those of classic Refsum Disease.

METHODS

Retrospective chart and digital photography review.

RESULTS

A 25-year-old woman with a diagnosis of infantile Refsum disease presented with progressively decreasing vision. Findings included a noncorpuscular pigmentary degeneration of both fundi, optic nerve head drusen, attenuated retinal vasculature, cataract, myopia, and esotropia. She was treated with a low phytanic acid diet, resulting in improved metabolic values on laboratory testing.

CONCLUSION

Infantile Refsum disease has clinical features and a pathophysiology distinct from classic Refsum disease, despite occasionally presenting for examination later in life. Ophthalmic and systemic distinctions between the two are important to consider for the ophthalmologist, who may be involved in the initial diagnosis of the patient.

The clinical spectrum of inherited diseases involved in the synthesis and remodeling of complex lipids. A tentative overview

Over one hundred diseases related to inherited defects of complex lipids synthesis and remodeling are now reported. Most of them were described within the last 5 years. New descriptions and phenotypes are expanding rapidly. While the associated clinical phenotype is currently difficult to outline, with only a few patients identified, it appears that all organs and systems may be affected. The main clinical presentations can be divided into (1) Diseases affecting the central and peripheral nervous system. Complex lipid synthesis disorders produce prominent motor manifestations due to upper and/or lower motoneuron degeneration. Motor signs are often complex, associated with other neurological and extra-neurological signs. Three neurological phenotypes, spastic paraparesis, neurodegeneration with brain iron accumulation and peripheral neuropathies, deserve special attention. Many apparently well clinically defined syndromes are not distinct entities, but rather clusters on a continuous spectrum, like for the PNPLA6-associated diseases, extending from Boucher-Neuhauser syndrome via Gordon Holmes syndrome to spastic ataxia and pure hereditary spastic paraplegia; (2) Muscular/cardiac presentations; (3) Skin symptoms mostly represented by syndromic (neurocutaneous) and non syndromic ichthyosis; (4) Retinal dystrophies with syndromic and non syndromic retinitis pigmentosa, Leber congenital amaurosis, cone rod dystrophy, Stargardt disease; (5) Congenital bone dysplasia and segmental overgrowth disorders with congenital lipomatosis; (6) Liver presentations characterized mainly by transient neonatal cholestatic jaundice and non alcoholic liver steatosis with hypertriglyceridemia; and (7) Renal and immune presentations. Lipidomics and molecular functional studies could help to elucidate the mechanism(s) of dominant versus recessive inheritance observed for the same gene in a growing number of these disorders.

The eye in metabolic diseases: clues to diagnosis

Ophthalmologic manifestations occur in various inborn errors of metabolism (IEM), including small molecule disorders and organelle disorders. In a minority of diseases the occurrence of eye abnormalities could be attributed to direct toxic mechanisms of abnormal metabolic products or accumulation of normal metabolites by errors of synthetic pathways or by deficient energy metabolism. The age of onset of ocular abnormalities in IEM is variable, but onset often begins from birth to childhood. The major IEM associated with eye abnormalities include errors of lipid metabolism, carbohydrate metabolism, protein metabolism, and metal metabolism. IEM disorders with ocular motor manifestations include lipid storage diseases, neurotransmitter disorders and respiratory chain disorders. The purpose of this article is to describe ocular phenotypes associated with IEM, focusing on those diseases in which the ocular involvement is seen relatively early in the course of the disease. As therapeutic approaches become available for certain groups of IEM, the need for early diagnosis is increasingly important.

PEROXISOMEBIOGENESISDISORDERS

The peroxisome biogenesis disorders (PBDs) comprise 12 autosomal recessive complementation groups (CGs). The multisystem clinical phenotype varies widely in severity and results from disturbances in both development and metabolic homeostasis. Progress over the last several years has lead to identification of the genes responsible for all of these disorders and to a much improved understanding of the biogenesis and function of the peroxisome. Increasing availability of mouse models for these disorders offers hope for a better understanding of their pathophysiology and for development of therapies that might especially benefit patients at the milder end of the clinical phenotype.

The eye as a window to inborn errors of metabolism

Ocular manifestations in inborn errors of metabolism occur in many diseases and may be associated with any part of all eye components. In a minority of diseases it is possible to attribute the eye symptoms to a single hereditary pathogenetic mechanism. More often the aetiological relationship of the ocular defects to the metabolic disease is unknown. Diverse pathogenetic mechanisms may act via a common pathological pathway inducing ocular damage. The occurrence of eye abnormalities in metabolic disorders suggests that they are associated with direct toxic actions, errors of synthetic pathways or deficient energy metabolism. In this review, metabolic disorders with major abnormalities in the cornea, lens, retina and optic nerve are presented. In all cases, an appropriate combined approach by the ophthalmologist, paediatrician/neurologist, geneticist and clinical biochemist is the only way to diagnostic success.

Juvenile macular dystrophy associated with deficient activity of fatty aldehyde dehydrogenase in Sjögren-Larsson syndrome

PURPOSE

To report the ocular manifestations associated with the Sjögren-Larsson syndrome in a series of patients with proven fatty aldehyde dehydrogenase deficiency. To emphasize the clinical importance of the ophthalmological features of the Sjögren-Larsson syndrome. To discuss the metabolic disturbances that might give rise to the ophthalmological picture.

METHODS

Fifteen patients with Sjögren-Larsson syndrome underwent a standardized ophthalmological examination. In patients of appropriate age, and who were able to cooperate, additional investigations were performed.

RESULTS

All patients exhibited bilateral, glistening yellow-white crystalline deposits that were located in the innermost retinal layers and appeared during the first 2 years of life. Repeated fundus photography in individual patients showed that the dots became more numerous as the patients got older. Photophobia, subnormal visual acuity, myopia, and astigmatism were found in most of the patients. Fluorescein angiography was performed in three patients and showed a mottled hyperfluorescence of the retinal pigment epithelium, without leakage. Color vision, electroretinography, and electro-oculography could be performed in only a small number of patients and showed no abnormalities. Visual evoked potentials were found to be abnormal in six of eight patients.

CONCLUSIONS

In Sjögren-Larsson syndrome, patients exhibit highly characteristic bilateral, glistening yellow-white retinal dots from the age of 1 to 2 years onward. The number of dots increases with age. The extent of the macular abnormality does not correlate with the severity of the ichthyosis or with the severity of the neurological abnormalities. A high percentage of patients shows additional ocular signs and symptoms, notably marked photophobia.

Retinal dystrophy in long chain 3-hydroxy-acyl-coA dehydrogenase deficiency

BACKGROUND

Long chain 3-hydroxyacyl-CoA-dehydrogenase (LCHAD) is one of the enzymes involved in the breakdown of fatty acids. A deficiency of this enzyme is associated with life threatening episodes of hypoketotic hypoglycaemia during prolonged fasting. Neuropathy and retinopigmentary changes were mentioned in only a few cases.

METHODS

The case histories of two girls, aged 8 and 15 years, with LCHAD deficiency are reported.

RESULTS

Both children with LCHAD deficiency exhibited extensive macular pigmentary depositions and a 'salt and pepper' scattering of pigment in their retinas. The patients have decreasing visual acuity.

CONCLUSION

The early recognition of LCHAD deficiency can increase the life expectancy in these patients through avoiding catabolism and through appropriate diets. Patients tend to be free of symptoms between attacks, however. Testing for the disorder, therefore, should be included in the diagnostic process for children with retinal dystrophy, in particular when other clinical symptoms are known to have occurred.

Neuronal ceroid lipofuscinosis in the Polish Owczarek Nizinny (PON) dog. A retinal study

Visual dysfunction and neurological symptoms were found in Polish Owczarek Nizinny (PON) dogs. Two dogs were examined, one at 2 years of age and the other one at 4 years. The oldest dog was totally blind. The 2-year-old dog developed mental disturbances and the 4-year-old dog became severely ataxic. Ophthalmoscopical findings were retinal hyper-reflectivity, attenuation of the retinal vessels and the presence of greyish to brown spots in the fundus. Electrophysiological and ultrastructural studies were performed in the 2-year-old dog. Scotopic ERG responses were absent, whereas 30 Hz cone flicker responses were recordable, although with an amplitude reduced to about 30% of the normal level. A slow negative potential replaced the c-wave, indicating a dysfunction of the RPE. Intracellular inclusions with a granular appearance or containing membranous fingerprint-like or curvilinear profiles, resembling ceroid, were found in different retinal cells. The RPE cells in the central areas were charged with autofluorescent material having similar structure, Photoreceptor degeneration was most severe in the central areas, corresponding to the RPE changes. It appears than the PON dog may provide a new animal model for neuronal ceroid lipofuscinosis.

Carbohydrate deficient glycoprotein syndrome type I: ophthalmic aspects in four Sicilian patients

Four patients with carbohydrate deficient glycoprotein (CDG) syndrome type I underwent ophthalmic examination. All of them had retinitis pigmentosa with extinguished scotopic electroretinogram. The importance of CDG syndromes as one of the metabolic causes of retinal dystrophy with 'bony spicule' pigment is stressed.