Trigenic COL4A3/COL4A4/COL4A5 pathogenic variants in Alport syndrome: a case report

Alport syndrome (AS) is a hereditary kidney disorder of type IV collagen caused by pathogenic variants in the COL4A3, COL4A4 and COL4A5 genes. Previously several cases of digenic AS, caused by two pathogenic variants in two of the three COL4A genes, have been reported. Patients with digenic AS may present with a more severe phenotype compared to patients with single variants, depending on the percentage affected type IV trimeric collagen chain. We report a newly discovered case of trigenic AS. A 52-year-old female presented with hematuria at the age of 24 years and developed hypertension by the age of 30. Over the years she developed chronic kidney disease; the most recent eGFR was 44ml/min/1.73m2. She has symmetric high-tone sensorineural hearing loss. Full genetic analysis revealed a heterozygous pathogenic variant c.2691del in COL4A3, a heterozygous pathogenic variant c.1663dup in COL4A4, and a complete heterozygous deletion of COL4A5. We describe the first patient with AS caused by pathogenic variants in all three COL4A genes, designated trigenic AS. This case report emphasizes the importance of examining all three COL4A genes, even in patients with a mild Alport phenotype, for optimal follow-up of the patient and adequate genetic counseling of family members.