Atypical Liver Ultrasound Image in a Boy with Autosomal Recessive Polycystic Kidney Disease (ARPKD) and New PKD1 Variant—A Case Report

<b>Background</b>: Autosomal recessive polycystic kidney disease (ARPKD) is a rare form of PKD that leads to the development of multiple renal cysts and hepatic fibrosis. <b>Aim</b>: The first documented case of large hepatic cyst associated with dual <i>PKHD1-PKD1</i> variants. <b>Case report</b>: We present the case of a 5-year-old boy with a kidney US image typical of ARPKD and numerous large cysts in the liver not typical for this disease. Genetic analysis revealed heterozygous missense mutations in the <i>PKHD1</i> gene (maternally, c.107C>T/p.Thr36Met in exon 3; paternally, c.4870C>T/p.Arg1624Rrp in exon 32) and an additional new variant in <i>PKD1</i> (maternally, c.5323G>A/p.Gly1775Ser in exon 32). Genetic tests excluded mutations in genes responsible for polycystic liver disease (PCLD). However, the presence of the <i>PKD1</i> mutation is clinically not clear due to the normal abdominal US image in the mother; it seems to be the most likely explanation for unusual phenotype in our patient. <b>Conclusions</b>: This case may contribute to the understanding of the phenotypic variability in ARPKD and the potential modifying role of mutations in other PKD-related genes. Comprehensive genetic panels are crucial for explaining atypical phenotypes and prognosis in patients with PKD.