INTRODUCTION
Renal coloboma syndrome (RCS) is an autosomal dominant disorder with high penetrance and variable expressivity.1 RCS is primarily characterized by renal dysplasia and abnormalities of the optic nerve.1,2
Although there is no formal diagnostic criteria for RCS, it is thought to be associated with a heterozygous pathogenic variant inPAX2 .1 50% of patients with clinical findings suggestive of RCS (e.g. renal and ocular malformations) have a mutation in the PAX2 gene.2 As a result of improved access to molecular genetic testing, more individuals with PAX2mutations have been identified with a wide phenotypic variability.2
Renal and ocular findings are reported in 92% and 72% of affected individuals respectively.1 Abnormalities in kidney structure and function are among the most frequent findings in individuals with PAX2 mutations, which include: renal dysplasia, multicystic dysplastic kidney and end-stage renal disease. Primary ocular findings involve optic nerve dysplasia that ranges from severe to mild.1,2
Reports of prenatal RCS findings have been limited, highlighting the importance of intrafamilial monitoring among affected individuals. Once a PAX2 pathogenic variant has been identified in a family, prenatal genetic testing for the familial variant becomes possible, in addition to screening through ultrasound (US), to detect any renal malformations and assess amniotic fluid levels.1 To date, only six case reports and one large series have been published on prenatal RCS findings.3-8 Of the six case reports, four involved terminated pregnancies as a result of prenatal US findings of fetal renal dysplasia, and/or oligohydramnios.3-5Common findings among all case reports include bilateral fetal renal hypoplasia and observed bilateral optic disc colobomas postnatally. Upon genetic testing, there is considerable variability in the PAX2gene variants, with most case reports having a de novo mutation.4,5,7,8 Notably, one case report presents a male with moderate-severe oligohydramnios for which an amnio-infusion of 250 ml of normal saline was performed. The remainder of the pregnancy was monitored with serial US examinations, leading to a live birth following that intervention.3
Bower et al reported one of the biggest RCS prenatal case series that added 13 prenatal cases to the literature.9 Six of the 13 fetuses were terminated given prenatal findings of renal hypoplasia, in addition to severe oligohydramnios. All six cases had parents confirmed with a pathogenic PAX2 variant. The other seven surviving cases had de novo mutations. Five out of the seven had normal amniotic fluid levels, while the other two had mild oligohydramnios, in addition to a renal hypoplasia or dysplasia. None of the 13 cases reviewed had self-resolving oligohydramnios.
We further add to the literature a report of mother and her newborn with RCS, both presenting prenatally with self-resolving severe oligohydramnios as an early prenatal finding.