Clinical Description
PAX2-related disorder is associated with abnormalities involving the kidneys and/or the eyes. The original PAX2-related disorder known as renal coloboma syndrome is characterized by hypodysplastic kidneys and optic nerve abnormalities (most commonly optic nerve dysplasia) with or without optic nerve or retinal coloboma [Sanyanusin et al 1995a, Schimmenti et al 1995, Schimmenti et al 2003].
Variability. The clinical findings vary even within families, with some family members having either renal manifestations or optic nerve abnormalities and others having both. The severity of renal malformations can range within a family from absence of clinical symptoms to severe fetal renal failure.
In some instances a detailed eye examination is necessary to reveal the ocular findings of PAX2-related disorder in individuals presenting with characteristic renal findings [Chung et al 2001, Nishimoto et al 2001, Salomon et al 2001] or renal evaluation is needed in individuals with characteristic eye findings [Parsa et al 2001].
A wide range of kidney and eye findings can be found in individuals with PAX2-related disorder (see Suggestive Findings).
Renal disease. Renal insufficiency/failure can occur at any age. The age at diagnosis of Stage 5 chronic kidney disease ranges from birth to 79 years.
The natural history of vesicoureteral reflux varies: in some individuals ureteral reimplantation has been required [Schimmenti et al 1995]; in others the reflux has spontaneously resolved [Ford et al 2001].
Eye abnormalities. Impaired visual acuity of one or both eyes is present in 75% of affected individuals; acuity ranges from light perception only to normal. Other findings can include nystagmus, myopia, and strabismus.
The natural history of visual acuity in individuals with PAX2-related disorder has not been prospectively studied. In some instances, significant changes in visual acuity have been reported. Visual acuity deteriorated in one person as a result of retinal detachment [Ford et al 2001]. One person reported acute vision loss resulting in a change of visual acuity from 20/80 to light perception only [Schimmenti et al 1995]; however, the cause of vision loss was unexplained as there was no evidence of detachment or macular changes [Schimmenti, unpublished observation].
Other. Less commonly reported findings in affected individuals include high-frequency hearing loss, soft skin, and ligamentous laxity. The age of onset and progression of hearing loss remain unknown and have not been evaluated prospectively. The hearing loss, when present, has been discovered in childhood and is bilateral high-frequency sensorineural hearing loss [Schimmenti et al 1995, Bower et al 2012].
Prenatal phenotype. Abnormalities including oligohydramnios/anhydramnios, cystic renal dysplasia, multicystic dysplastic kidneys, and renal hypoplasia were reported on prenatal ultrasound in 18 individuals with PAX2 pathogenic variants [Bower et al 2012]. Seven fetuses with a confirmed PAX2 pathogenic variant and severe prenatal renal failure (Potter sequence) have been reported [Martinovic-Bouriel et al 2010, Bower et al 2012]. In several instances, parents with mild renal disease had pregnancies where the fetus presented with severe renal disease in utero.
Genotype-Phenotype Correlations
Review of all reported cases to date does not reveal a consistent genotype/phenotype correlation. This is most dramatically illustrated by the tremendous intrafamilial variability in the severity of ocular and renal findings. To date, no clear evidence suggests that the location of a pathogenic variant (paired domain, octapeptide domain, partial homeodomain, or transactivation domain) or the type of pathogenic variant (missense variant, nonsense variant, or gene deletion) consistently predicts the clinical phenotype.
Penetrance
Only one individual with a pathogenic variant in PAX2 in whom renal and ophthalmologic examinations were performed and documented as normal has been reported [Bower et al 2012]. Thus, penetrance appears to be greater than 99%. In individuals with pathogenic variants in PAX2, the penetrance of eye malformations is at least 77% [Bower et al 2012]. This should be viewed as a minimum figure, as fully 21% of individuals with PAX2 pathogenic variants have not had a dilated eye examination to evaluate for subclinical abnormalities of the optic nerve. The penetrance for renal malformations or renal disease is at least 92%. Again, this figure should be viewed as a minimum, as some individuals with pathogenic variants have not had full renal evaluations.
Nomenclature
Terms previously used for renal coloboma (papillorenal syndrome) syndrome:
Coloboma-ureteral-renal syndrome
Optic nerve coloboma with renal disease
Coloboma of the optic nerve with renal disease
Optic coloboma-vesicoureteral reflux-renal anomalies
Controversy regarding the naming of this syndrome has caused confusion in the field. The condition was named renal coloboma syndrome based on the presence of kidney abnormalities and the optic nerve abnormalities described by the ophthalmologists who identified the original families found to have PAX2 pathogenic variants [Sanyanusin et al 1995a, Sanyanusin et al 1995b]. In 2001, Parsa et al identified a family with similar optic nerve and renal abnormalities where no variants in PAX2 were identified and suggested that the name of the condition be changed to papillorenal syndrome; it is unclear if the two entities are related.