Axenfeld–Rieger syndrome is a rare autosomal dominant disorder, which affects the development of the teeth, eyes, and abdominal region.
Axenfeld–Rieger syndrome is part of the so-called iridocorneal or anterior segment dysgenesis syndromes, which were formerly known as anterior segment cleavage syndromes, anterior chamber segmentation syndromes or mesodermal dysgenesis. Although the exact classification of this set of signs and symptoms is somewhat confusing in current scientific literature, most authors agree with the classification cited here. Axenfeld Anomaly is known as the development of a posterior embryotoxon, associated with strands of the iris adhered to a Schwalbe line that has been displaced anteriorly, which when added to glaucoma is called Axenfeld Syndrome. Rieger's Anomaly is defined by a universe of congenital anomalies of the iris, such as iris hypoplasia, corectopia or polycoria. When systemic findings are added to Rieger's anomaly, such as bone, facial and/or dental defects, it is known as Rieger syndrome. The combination of both entities gives rise to the Axenfeld-Rieger Anomaly when there are no systemic abnormalities and Axenfeld-Rieger Syndrome when there are.
Axenfeld-Rieger Syndrome, is a rare disease that affects the eye bilaterally, with an estimated prevalence of 1/200,000 people, without gender predilection, and is characterized by autosomal dominant inheritance with complete penetrance of variable expressivity. The genes that have been identified in approximately 50% of cases are PITX2 and FOXC1. Given the important hereditary factor, it is important to evaluate the most direct members of the family.
To explain the ocular alterations, there is a theory of the mechanism postulated by Shields et al., which implies an arrest in the migration of neural crest cells towards the third trimester of gestation, which leads to the persistence of primordial endothelial tissue in the iris and anterior chamber angle. Contraction of these membranes after birth lead to the progressive changes seen in some patients. This primordial endothelium also generates an excessive and atypical basement membrane, especially near the limbal corneal junction, which accounts for the prominent Schwalbe line. In the case of secondary glaucoma, it would be the consequence of dysgenesis in the chamber sinus.
Signs and symptoms
Disease manifestations:
Regarding the age of diagnosis, this differs according to the intensity of the symptoms, ranging from asymptomatic to florid symptoms, characterized by ocular and systemic diseases, affecting multiple organs that have in common their origin in the neural crest.
Eye manifestations: Bilateral ocular manifestations are usually pathognomonic of the disease. In the case of children who develop glaucoma, they may attend the consultation with signs and symptoms of buphthalmos, photosensitivity, tearing, corneal decompensation, which associated with poor vision, can be completed with a strabismus. In the case of the adult, there is a greater chance of not presenting symptoms, so an ophthalmological control may be required to detect the problem. Using a slit lamp, a posterior embryotoxon characterized by a prominent anteriorly displaced Schwalbe's ring near the temporal corneal limbus can be revealed. The unexpected finding of a posterior embryotoxon as a single whitish irregular arcuate ridge, on routine examination, is not necessarily a diagnosis of ARS, as this occurs in a percentage estimated in the literature from 8% to 15% of the normal population. In the case of gonioscopy, we can observe that the extension of the posterior embryotoxon can be greater and be present in the 360○, with a variable thickness of the annulus and unusually detached and hanging within the anterior chamber. Regarding the iris, we can observe peripheral extensions to Schwalbe's line, which can be thin or thick and extend over the trabecular meshwork, obscuring the scleral spur and even pulling the iris and producing corectopia in iris tissue that can range from atrophy mild stromal to the presence of uveal ectropion, pseudopolycoria or even absence of iris or pseudoacorea. These chamber sinus anomalies predispose half of the cases to open-angle glaucoma, which can manifest throughout life and therefore require regular ophthalmological check-ups. Other related anomalies are strabismus due to alteration in the insertions of the extraocular muscles or secondary to amblyopia, and with a predisposition to exotropia and retinal detachment.