Rethinking genotype-phenotype correlations in papillorenal syndrome: a case report on an unusual congenital camptodactyly and skeletal deformity with a heterogeneous PAX2 mutation of hexanucleotide duplication

Papillorenal syndrome (PRS), an autosomal dominant inherited condition, is clinically featured by renal hypoplasia and optic nerve dysplasia. Based on current knowledge of genotype-phenotype correlations in PRS, mutations in the Paired box 2 (PAX2) gene have been recognized as a critical pathogenesis of typical renal and optic disease manifestations. However, little information is currently available on the skeletal abnormalities of PRS and the potential contribution of PAX2 mutations. Here, we present a case of a 10-year-old female PRS patient with the typical features of chronic renal failure and severe myopia, but was unexpectedly discovered camptodactyly of her left middle finger which affects the proximal interphalangeal joint. Pathologically, the camptodactyly was further indicated by radiology as a skeletal deformity, demonstrating a decline of bone mineral density and disappearance of joint space. Molecular diagnostics revealed a heterozygous mutation, 220_225dup, in the exon 3 of her PAX2 gene, which is de novo considering the lack of this mutation in her non-consanguineous parents. This mutation leads to duplication of glutamic acid at position 74 and tyrosine at position 75 in PAX2 protein, which may influence the DNA-binding function. Besides, the absence of Spalt like transcription factor 4 (SALL4) mutation excluded the diagnosis of acro-renal-ocular syndrome (AROS), of which clinical characteristics are similar to our patient's. This case unravels a previously unrecognized phenotype of camptodactyly due to a significant skeletal deformity of PRS with a heterogeneous PAX2 mutation of hexanucleotide duplication. This report challenges against the current belief of genotype-phenotype correlations in PRS.