A Novel Synonymous Variant of PAX2 in Monochorionic Diamniotic Twins With Bilateral Renal Agenesis: A Case Report and Literature Review

Abstract

Background: Paired Box 2 (PAX2, NM_000278.5) encodes paired box gene 2, one of many human homologs of the Drosophila melanogaster gene prd. PAX2-related disorder is an autosomal dominant disorder associated with renal and eye abnormalities.

Methods: In this study, both monochorionic diamniotic twins presenting bilateral renal agenesis were subjected to investigation. The pregnancy was terminated and muscular tissue of the fetus was analyzed by trio whole exome sequencing (WES). The target sequence was verified by Sanger sequencing at the genome level. In vitro Minigene model was constructed and the transcribed cDNA was subjected to Sanger sequencing to explore the splicing effect of the suspected mutation.

Results: The synonymous mutation PAX2 c.792G>A was detected in both twins, but not in the parents or the family's firstborn. Although this mutation did not alter the amin acid sequence, minigene splice analysis confirmed that c.792G>A resulted in exon 6 skipping, leading to aberrant mRNA splicing.

Conclusion: PAX2 c.792G>A is the first pathogenic synonymous mutation ever documented. It has a significant impact on mRNA splicing and leads to developmental abnormalities. This case highlights the importance of clinical phenotyping as well as comprehensive genetic analysis during genetic testing, including evaluation of synonymous mutations.

Keywords: PAX2; bilateral renal agenesis; minigene analysis; prenatal diagnosis; synonymous mutation.

FIGURE 1

Pedigree chart.

FIGURE 2

pcMINI vector detection results (A) Schematic diagram of pcMINI minigene vector construction; (B) Agarose gel electrophoresis of RT‐PCR transcription analysis, with bands in 293T and HeLa cells labeled as a and b; (C) Schematic representation of pcMINI minigene splicing; (D) Sequencing results corresponding to the spliced bands.

FIGURE 3

pcMINI‐C vector detection results (A) Schematic diagram of pcMINI‐C minigene vector construction; (B) Agarose gel electrophoresis of RT‐PCR transcription analysis, with bands in 293T and HeLa cells labeled as a and b; (C) Schematic representation of pcMINI‐C minigene splicing; (D) Sequencing results corresponding to the spliced bands.

FIGURE 4

Ultrasound findings Serial prenatal ultrasounds demonstrated bilateral renal absence with characteristic adrenal “lying‐down” signs in both fetuses. The red arrow points to the “lying‐down” adrenal gland (A) 15 + 2 gestational weeks; (B) 18 + 2 gestational weeks. (C) Absence of bilateral renal arteries of both fetuses at 15 + 2 weeks (F1: Fetus 1; F2: Fetus 2).

FIGURE 5

Sanger sequencing results.

FIGURE 6

Schematic diagram corresponding to the structure of PAX2 gene (NM_000278.5) and PAX2 protein (NP_000269.3). This figure is not to scale.