Rieger syndrome is an autosomal-dominant condition characterized by ocular and dental abnormalities, mainly hypodontia and microdontia. A wide spectrum of additional systemic anomalies, such as facial malformations and umbilical defects, may be found. The most common ocular defects are bilateral hypoplasia of the iris, a prominent Schwalbe line with iris strands extending over the angle to the Schwalbe ring, and corectopia.1
We describe here an unusual presentation of Rieger syndrome occurring in identical twins. Both had the characteristic dental defects but only one of the twins had unilateral eye involvement.
A 5-year-old girl was referred to our department because of corectopia and glaucoma in her left eye. She was born after an uneventful twin pregnancy. The ocular anomaly was present since birth but had not caused any symptoms. Glaucoma was detected at the age of 4 years. On ocular examination, the visual acuity was 20/20 in both eyes. The intraocular pressure (IOP) by applanation was 12 mm Hg in the right eye and 30 mm Hg in the left eye. Slit-lamp and funduscopic findings of the right eye were normal. Slitlamp examination of the left eye revealed a normal cornea, corectopia, hypoplastic smooth and cryptless iris with retroillumination defects, and a 360-degree ectropion uveae (Fig 1). Gonioscopy of the left eye demonstrated an open angle with visible trabecular meshwork and high iris insertion. Funduscopic examination was normal. The patient was normally developed for her age. The physical examination was within normal limits except for dental abnormalities that included microdontia, micrognathia, teeth defects, and malocclusion. Her 24 deciduous teeth had various slope, and the upper incisors were hypoplastic and spaced (Fig 2).
Ocular and physical findings were consistent with the diagnosis of Rieger syndrome. Because of glaucoma in the left eye, timolol 0.5% and pilocarpine 4% were given, which controlled the IOP.
FIGURE 1: Teeth of the patient (identical to the teeth of her twin sister). Note hypoplastic and spaced upper incisors and microdontia.
FIGURE 2: Left eye of the patient. Note smooth, cryptless iris, ectropion uveae, and corectopia.
There was no family history of glaucoma or other eye malformation. The patients' parents and brother were in good health without any abnormalities of the eyes and teeth. The twin sister of the proband resembled her remarkably and had similar dental abnormalities (microdontia, micrognathia, and malocclusion), but her ocular findings were normal. Dermatoglyphic patterns of the sisters were almost identical. Their blood groups and subgroups were identical (A + , M + , N + , c + , C + , E-), as were their HLA alleles (Al, A24, B35, B37, BW4, BW6, CW4).
Rieger anomaly is characterized by a prominent Schwalbe line with attached iris strands, iris hypoplasia, iris pigment epithelial defects, polycoria, ectropion uveae, and corectopia. Glaucoma occurs in slightly more than half of the cases. The cornea is often normal but microcornea and macrocornea may be seen. Uncommonly other ocular malformations may be associated, such as lens opacities, aniridia, disc anomalies, chorioretinal colobomas, macular degeneration, choroidal hypoplasia, and retinal detachment. The combination of dental and facial defects with Rieger anomaly is called Rieger syndrome. The most common dental abnormalities are microdontia, hypodontia, and oligodontia. Facial abnormalities include maxillary hypoplasia, telecanthus, and broad flat nose. Based on the clinical and histologic observations, it is now believed that Rieger anomaly results from developmental arrest of certain anterior segment structures derived from neural crest cells. This concept also helps to explain monocular manifestations such as teeth and facial bone anomalies since these structures also have a neural crest origin.1 The sisters described here were homozygotic twins as proved by their identical dermatoglyphic patterns and blood groups. They had typical Rieger syndrome dental anomalies (microdontia, malocclusion, and micrognathia), but only one sister presented the characteristic ocular features of Rieger anomaly, ie, iridic hypoplasia, corectopia, ectropion uveae, abnormal chamber angle, and latent glaucoma. Also of interest is the fact that the ocular abnormalities were unilateral. Rieger syndrome is a bilateral condition. Unilateral ocular involvement has been reported in Rieger syndrome only once.2 The presence of dental anomaly of Rieger syndrome without the eye signs in one of the twins is another outstanding feature found in the present cases. To our knowledge, in published pedigrees of Rieger syndrome, there has not been found a family member who had the dental anomalies and not the eye manifestations of the syndrome.
The mode of transmission of Rieger syndrome is autosomal dominant,3 although autosomal recessive or sporadic cases have been reported.4·5 As the family history in our patient was negative for the syndrome, it is proposed that the condition arose de novo as a mutation.
In view of the dental abnormalities in both twins and of unilateral Rieger anomaly in one of them, it seems to us that both suffer from Rieger syndrome with variable expressivity.
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