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Teen referred for problems with refraction in both eyes
The patient had an extensive medical history. Mottling of the retinal pigment epithelium was noted in the macula of both eyes.
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A 16-year-old Hispanic boy was referred to our retina office when he could not be refracted better than 20/60 in either eye by a general ophthalmologist. Upon questioning, he indicated that he had poor night vision and was photophobic, but there was no family history of eye disease. Medical history was notable for mild mental retardation, low testosterone levels, and surgical removal as a toddler of a sixth finger on each hand and a sixth toe on each foot (Figure 1) present from birth. On review of systems, his parents noted he has anosmia, a poor sense of smell.
On examination, best corrected visual acuity was 20/60 in the right eye and 20/70 in the left eye. There was no afferent pupillary defect, visual fields were full to finger confrontation, and motility was full and orthophoric. Anterior segment examination was unremarkable. Both optic nerves appeared slightly pale without swelling. Mottling of the retinal pigment epithelium was noted in the macula of both eyes (Figure 2). No cystoid macular edema was appreciated. A pattern of peripheral bone spicule hyperpigmentation was noted in the mid-peripheral retina. There was no vitreous cell. Fundus autofluorescence imaging disclosed mottled macular hyper- and hypo-autofluorescence (Figure 3). An electroretinogram was performed and documented a generalized rod-cone dysfunction.
Figure 1. The patient had a sixth toe on each foot surgically removed as a toddler.
Source: Fine HF
Figure 2. Color fundus photograph showed mottling of the retinal pigment epithelium in the macula.
Source: Fine HF
Figure 3. Fundus autofluorescence imaging disclosed mottled macular hyper- and hypo-autofluorescence.
Source: Fine HF
The diagnosis
Bardet-Biedl syndrome (BBS) is a human ciliopathy, a fascinating group of genetic disorders arising from dysfunction of cells containing cilia, specialized hair-like organelles. BBS is characterized by polydactyly, obesity, hypogonadism, renal dysfunction, mental retardation and retinal degeneration. These six major disease features are often accompanied by minor features, including anosmia, hearing loss, cardiovascular abnormalities, speech deficits and hepatic defects, among others. The incidence has been reported on the order of one in 160,000.
Joseph Kristan
Ocular findings in BBS often include a clinical picture of retinitis pigmentosa that begins in childhood. Atrophic macular changes often predominate over peripheral pigmentary changes. Disc pallor and vascular attenuation are common. The prognosis is poor, with roughly three-quarters of patients legally blind by the second or third decade of life. Electroretinographic findings may show a rod-cone dystrophy or even extinguished responses. Overlap syndromes include Laurence-Moon syndrome (also termed Laurence-Moon-Bardet-Biedl syndrome), McKusick-Kaufman syndrome and Biemond syndrome type 2.
To date, there are at least 15 genes implicated in the disease pathogenesis of BBS. While the function of all of these genes is heterogeneous and not yet fully elucidated, many appear to be involved in ciliary transport and intracellular trafficking. Currently, no effective treatments exist for ocular disease in BBS.
References:
- Adams NA, Awadein A, Toma HS. The retinal ciliopathies. Ophthalmic Genet. 2007;28(3):113-125.
- Badano JL, Mitsuma N, Beales PL, Katsanis N. The ciliopathies: an emerging class of human genetic disorders. Annu Rev Genomics Hum Genet. 2006;7:125-148.
- Blacque OE, Leroux MR. Bardet-Biedl syndrome: an emerging pathomechanism of intracellular transport. Cell Mol Life Sci. 2006;63(18):2145-2161.
- Daniels AB, Sandberg MA, Chen J, Weigel-Difranco C, Hejtmancik JF, Berson EL. Genotype-phenotype correlations in Bardet-Biedl syndrome [published online ahead of print March 12, 2012]. Arch Ophthalmol. doi:10.1001/archophthalmol.2012.89.
- Zaghloul NA, Katsanis N. Mechanistic insights into Bardet-Biedl syndrome, a model ciliopathy. J Clin Invest. 2009;119(3):428-437.
For more information:
- Joseph Kristan can be reached at joseph.kristan@gmail.com.
- Howard F. Fine, MD, MHSc, can be reached at Retina-Vitreous Center, 10 Plum St., Suite 600, New Brunswick, NJ 08901; 732-220-1600; email: h_f_fine@yahoo.com.
- Disclosures: Mr. Kristan has no relevant financial disclosures. Dr. Fine is a consultant or speaker for Genentech, Regeneron, Allergan and Ophthotech.