Clinicopathological Report of Retinitis Pigmentosa with Vitamin E Deficiency Caused by Mutation of the α-Tocopherol Transfer Protein Gene

Clinicopathological Report of Retinitis Pigmentosa with Vitamin E Deficiency Caused by Mutation of the -Tocopherol Transfer Protein Gene Jijing Pang*, Motohiro Kiyosawa*, Yuko Seko*, Takanori Yokota†, Seiyo Harino‡ and Jun-ich Suzuki§ *Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University, Graduate School, Tokyo, Japan; †Department of Neurology, Tokyo Medical and Dental University, School of Medicine, Tokyo, Japan; ‡Yodogawa Christian Hospital, Osaka, Japan; § Department of Ophthalmology, Sapporo Medical College, Sapporo, Japan

Purpose: To discuss the clinicopathological findings in a patient with retinitis pigmentosa (RP) accompanied by a vitamin E deficiency caused by an H101Q mutation in the -tocopherol transfer protein (-TTP) gene. Case: The clinical course of this patient was followed by conventional ophthalmological examinations over a 3-year period. After the patient died from pancreatic cancer, the eyes were obtained, and examined by light and electron microscopy. Observations: The patient complained of night blindness subsequent to adult-onset ataxia, although the ataxia was very mild. His visual acuity was 0.6 OU, and ophthalmoscopy revealed RP sine pigmento. Ring scotomas were detected, and the electroretinography, electro-oculography, and dark-adaptation were altered. Fluorescein angiography showed granular hyperfluorescence around the macula. No progression of the visual and neurological symptoms was observed during the 10 years he was taking oral vitamin E. Histopathological examination revealed the loss of the outer and inner segments of the photoreceptors in the area corresponding to the ring scotoma, as well as a disorganization and shortening of the outer segments in the peripheral retina. Conclusions: We conclude that the clinical and pathological findings in the eyes of this patient having RP with vitamin E deficiency caused by an H101Q mutation are similar to those of common autosomal recessive RP. However, special attention is required in making a diagnosis of RP with vitamin E deficiency because RP with vitamin E deficiency is medically treatable. The mild Friedreich-type ataxia accompanying the RP may be helpful in identifying this disease. Jpn J Ophthalmol 2001;45:672–676 © 2001 Japanese Ophthalmological Society Key Words: -Tocopherol transfer protein gene mutation, night blindness, pathology, retinitis pigmentosa sine pigmento, vitamin E deficiency.

Introduction Vitamin E (-tocopherol) is one of the most potent lipid-soluble antioxidants in the retinal biologiReceived: February 16, 2001 Current address for Jijing Pang: Eye Research Institute, Oakland University, 422 Dodge Hall, Rochester, MI 48309-4401, USA Correspondence and reprint requests to: Motohiro KIYOSAWA, MD, PhD, Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University, Graduate School, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8519, Japan Jpn J Ophthalmol 45, 672–676 (2001) © 2001 Japanese Ophthalmological Society Published by Elsevier Science Inc.

cal membranes and contributes to membrane stability. Deficiency of this antioxidant may be critical for the maintenance of the outer segment membranes that contain a very high percentage of polyunsaturated fatty acids surrounded by a well-oxygenated environment.1 Natural isomers of vitamin E (, , , and -tocopherol) are absorbed from the small intestine and transported in chylomicrons to the liver. Only -tocopherol is incorporated into nascent, very low-density lipoproteins and can then enter the cir0021-5155/01/$–see front matter PII S0021-5155(01)00425-7

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Figure 1. (A) Fundus photographs: Both fundi showing tigroid changes without bone corpuscle-shaped pigments. Optic discs appear waxy pale with large crescents in both eyes. Arteries are moderately narrowed. (B) Goldmann kinetic visual fields showing ring scotoma in right eye and relative ring scotoma in left eye.

culation. -Tocopherol transfer protein (-TTP) is a cytosolic liver protein that is believed to function in this selective incorporation of -tocopherol. With normal functioning of -TTP, the efficient recycling of vitamin E is maintained and the rapid elimination of vitamin E is prevented.1 We have recently found a point mutation (H101Q) in the -TTP gene in 4 patients with Friedreich’s ataxia and retinitis pigmentosa (RP) of different severity.1,2 All of these patients showed a vitamin E deficiency, and the deficiency was shown to be not due to an abnormal absorption of vitamin E but to an increase of its elimination from the serum. The expression of -TTP gene is not only in the liver but also in the retina, and the possible role of -TTP in the retina has been discussed in relation to the etiology of RP.1 It was generally believed that the deficiency of

serum vitamin E plays a major role in the pathophysiology of the RP, and oral administration of vitamin E appeared to halt the progression of the visual and neurological symptoms.1–3 Yokota et al1, using light microscopy in a postmortem study of one of their patients (case 3), reported a severe dying-back type of degeneration of the posterior column, massive accumulation of lipofuscin in the dorsal root ganglion cells, and loss of photoreceptor outer segments in the retina.3 We discuss the pathophysiology of this type of RP with a point mutation (H101Q) in the -TTP gene.

Case Report The patient complained of difficulty in walking at the age of 52, and noticed night blindness when he

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was 56 years old. A diagnosis of a Friedreich-like ataxia with vitamin E deficiency was made when he was 62 years old. He was found to have a mutation in the -TTP gene; a single nucleotide alteration in the second of the five coding exons was detected. The patient was homozygous for a thymine-to-guanine (T-to-G) transversion at nucleotide position 303 of the -TTP cDNA. The serum level of vitamin E was 2.1 g/mL (normal  5.5). Oral administration of all-rac--tocopheryl acetate (300 IU/day) was initiated, and resulted in an increase in the serum vitamin E concentration to normal levels. The neurological deficits included ataxia, areflexia, and impairment of deep sensations. However, the symptoms were mild and he could walk without assistance during the 10 years after the onset. At the age of 69, the patient, complaining of night blindness, was referred to the ophthalmology clinic in Tokyo Medical and Dental University for a detailed eye examination. His visual acuity was RE: 0.04 (0.6 x 6.00 D cyl 3.00 D AX 90 ), LE: 0.04 (0.6 x 6.50 D cyl 3.00 D AX 90 ). The intraocular pressure was 12 and 15 mm Hg in the right and left eyes, respectively, and color vision was normal by the Ishihara color plates. There were no obvious changes in the anterior segment, and ophthalmoscopy revealed tigroid changes without bone corpuscle pigmentation in the posterior pole of both eyes. The optic discs appeared waxy pale with a temporal conus in both eyes. Slight attenuation of the retinal vessels was also found (Figure 1A). Goldmann kinetic visual fields showed a ring scotoma in the right eye and an incomplete ring scotoma in the left eye (Figure 1B). Negative electroretinograms (ERGs) were recorded, and electrooculography disclosed a subnormal Arden ratio of 142% and 133% in the right and the left eyes, respectively. Dark-adaptation was also subnormal. Fluorescein angiography showed hyperfluorescence around the macula that corresponded to the ring scotoma obtained by Goldmann kinetic visual field examination. No progression of the visual impairment was detected during the 3 years from our first examination until his death at age 72 from pancreatic cancer. Histopathological examinations by light and electron microscopy showed that the changes involved mainly the photoreceptor layer although other layers of the retina and the choriocapillaris were also affected. In the area corresponding to the ring scotoma, the inner and outer segments were virtually absent and the photoreceptors were reduced in number. The other layers of the neuroretina were also thin and atrophic. Atrophy of the choriocapillaris was obvious (Figure 2A). In the same region, transmission electromicroscopy showed that the photoreceptors had disap-

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peared completely and the outer limiting membrane was in contact with the retinal pigment epithelium (RPE). The RPE was intact in this part of the retina, and showed significant accumulation of lipofuscin deposits (Figure 2B). In the middle to peripheral regions of the retina, the outer segments of the photoreceptors were shortened and disoriented. The other layers of the neuroretina were also thin and atrophic. The choriocapillaris was partially atrophic (Figure 2C). Electron microscopy confirmed the disorientation of the photoreceptor outer segments in this part of the retina. In contrast, the RPE was almost normal, although large vacuoles could be observed in some of the RPE cells (Figure 2D).

Discussion This patient with an H101Q mutation in the -TTP gene showed mild vitamin E deficiency with a late onset, chronic course of ataxia, followed by visual impairment 4 years after the onset of ataxia. Decreased visual acuity, ring scotomas, electrophysiological abnormalities, and nonpigmentary retinopathy were found. The histopathological findings were quite apparent and the main change was the loss of the photoreceptor layer. In contrast, the RPE was relatively well-preserved and normal phagocytosis could still be observed (data not shown) although most parts of the neuroretina were involved. Transmission electron microscopy showed significant accumulation of lipofuscin deposits in the RPE, which is compatible with the findings in the dorsal ganglion cells.3 The lipofuscin accumulation is probably an aging change. Similar histopathological changes exist not only in RP patients, but also in vitamin E deficient rats4 and dogs.5 The dog model, the one more comparable with our case, showed segmented retinal degeneration clinically and degeneration of the photoreceptors, outer nuclear layer, and outer plexiform layer in the severely affected regions, and loss of the outer segments in the less affected regions of the retina. Degeneration of photoreceptors was the common finding in these different animal models and in our case. The pathogenesis of RP in patients with the H101Q mutation in -TTP gene remains unknown, but there are several possible explanations. One explanation is that H101Q mutation causes loss of function of -TTP, and the vitamin E deficiency results in the RP-like changes. This possibility is supported by the similarity in the histopathological results to those of vitamin E deficient animals. The RP changes in patients with missense mutations are usually detected in their late adult-

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Figure 2. (A) Light photomicrograph from macular region showing that photoreceptors are reduced in number and inner and outer segments are virtually absent. Choriocapillaris is also atrophic. Hematoxylin-eosin stain. Bar 20 m. (B) Electron micrograph of macular region showing that outer and inner segments of photoreceptor are lost and outer limiting membrane is in contact with retinal pigment epithelium (RPE). RPE appears similar to that in peripheral part of retina although accumulation of lipofuscin granules is apparent. Bar 1 m. (C) Light photomicrograph of the peripheral retina showing shortened and disoriented outer segments of the photoreceptors. Hematoxylin-eosin stain, Bar 20 m. (D) Electron micrograph of peripheral retina showing disoriented photoreceptor outer segments. Retinal pigment epithelium is almost normal although some large vacuoles can be observed. Bar 1 m.

hood following the late onset of ataxia.2 In support of this relationship between the long duration and RP changes, it required as long as 10 months to detect mild attenuations of the ERGs in vitamin E deficient rats that had already exhibited ataxia.6 A second possible reason for the discrepancy in onset of RP and ataxia is that the mutant -TTP present in the retina3 was responsible for the development of the RP changes. Although the physiological function of -TTP in the retina is still unknown, the phenotypic variation could be explained if the mutant -TTP

gains some adverse property and a loss in function of retinal -TTP due to the null mutations is compensated for by some other mechanism. In our previous reports, we suggested that oral administration of vitamin E appeared to halt the progression of visual and neurological manifestation.1,2 Amemiya4 reported that rats fed a vitamin E deficient diet for a period of 6 months showed vesiculation of the photoreceptor outer segments, and this change could be corrected by the administration of vitamin E. However, rats fed a vitamin E de-

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ficient diet for as long as 8.5–18 months showed severely decreased or even absent photoreceptor inner and outer segments, and these changes could not be reversed by vitamin E.4 These findings suggest that the early diagnosis and administration of vitamin E may be critical for the prognosis of vitamin E deficiency caused by a mutation in the -TTP gene, although we could not clearly demonstrate the effectiveness of oral administration of vitamin E in our patient because of a relatively short observation period.

The authors thank Mrs. S. Ichinose and Dr. T. Uchihara for their technical assistance. We are also grateful to Dr. M. Tamai and Dr. D. Hamasaki for their helpful comments on this manuscript.

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References 1. Yokota T, Shiojiri T, Gotoda T, et al. Friedreich-like ataxia with retinitis pigmentosa caused by the His 101 Gln mutation of the -tocopherol transfer protein gene. Ann Neurol 1997;41:826–32. 2. Yokota T, Shiojiri T, Gotoda T, et al. Retinitis pigmentosa and ataxia caused by a mutation in the -tocopherol transfer protein gene. N Engl J Med 1996;335:1770–1. 3. Yokota T, Uchihara T, Kumagai J, et al. Postmortem study of ataxia with retinitis pigmentosa by mutation of the alpha-tocopherol transfer protein gene. J Neurol Neurosurg Psychiatry 2000;68:521–5. 4. Amemiya T. Effect of vitamin E administration on photoreceptor outer segment and retinal pigment epithelium of vitamin E deficient rats. Int J Vitam Nutr Res 1981;51:114–8. 5. Hayes KC, Rousseau JE Jr, Hegsted DM. Plasma tocopherol concentrations and vitamin E deficiency in dogs. J Am Vet Med Assoc 1970;157:64–71. 6. Goss-Sampson MA, Muller DPR, Kriss A. Abnormalities of the electroretinogram and visual-evoked potential in vitamin E deficient rats. Exp Eye Res 1991;53:623–7.