Mutational Landscape of Primary Hyperoxaluria in Morocco: Update and Implications for Diagnosis

Introduction: Primary hyperoxaluria (PH) is a rare autosomal recessive disease characterized by an excess of oxalate, which results in nephrolithiasis, nephrocalcinosis, and ultimately, renal failure and systemic oxalosis. There are 3 forms of PH, named types 1, 2, and 3, caused by variants in the AGXT, GRHPR, and HOGA1 genes, respectively. In Morocco, where consanguinity is common, recurrent variants, mainly affecting the AGXT gene, have been documented; however, the overall molecular profile of PH remains poorly characterized. We aim here to describe the mutational landscape of PH in Morocco and to provide an accurate diagnostic approach. Methods: We analyzed 132 patients referred over 10 years for PH using a stepwise strategy. A step 1 test involved Sanger sequencing of exon 7 of the AGXT gene, followed by sequencing of exons 1, 2, and 10 of the AGXT gene. The step 2 analysis consists of a customized gene panel targeting the three PH-associated genes. Unresolved cases underwent whole-exome sequencing as a third step. Results: First-line Sanger sequencing identified biallelic pathogenic or likely pathogenic AGXT variants in 95 of 132 patients suspected of PH, corresponding to a diagnostic yield of 72%. Additional molecular diagnoses obtained through targeted PH panel sequencing and WES increased the final cumulative diagnostic yield to 78%. Twelve distinct variants were characterized by Sanger sequencing, with the c.731T>C in exon 7 of the AGXT gene, emerging as the most prevalent variant, supporting its founder effect in this population. Other variants were predominantly located in exons 7, 10, 2, and 1, highlighting mutation hotspots in this population. In unresolved cases, next-generation sequencing (NGS), including targeted gene panels and exome sequencing, uncovered additional pathogenic variants in the AGXT gene and variants in other genes associated with PH-like phenotypes. Conclusions: These results highlight the need for a simplified, exon-focused diagnostic strategy, particularly in resource-limited settings like Morocco.