Acute intermittent porphyria (AIP) is a rare autosomal dominant porphyrin metabolic disease caused by a mutation in the hydroxymethylbilane synthase (HMBS) gene. This study aimed to explore the clinical manifestations of a patient with AIP, to identify a novel HMBS gene mutation in the proband and some of her family members, and to confirm the pathogenicity of the variant.A 22-year-old Chinese woman developed severe abdominal pain, lumbago, sinus tachycardia, epileptic seizure, hypertension, and weakness in lower limbs in March, 2018. Biochemical examinations indicated hypohepatia and hyponatremia. Her last menstrual period was 45 d prior to admission, and she was unaware of the pregnancy, which was confirmed by a pregnancy test after admission. Sunlight exposure of her urine sample for 1 h turned it from yellow to wine red. Urinary porphyrin test result was positive. Based on these clinical manifestations, AIP was diagnosed. After increasing her daily glucose intake (250-300 g/d), abdominal pain was partially relieved. Three days after hospitalization, spontaneous vaginal bleeding occurred, which was confirmed as spontaneous abortion; thereafter, her clinical symptoms completely resolved. Genetic testing revealed a novel heterozygous splicing variant of the HMBS gene in exon 10 (c.648_651+1delCCAGG) in the proband and four other family members. The pathogenicity of the variant was verified through bioinformatic methods and a minigene assay.We identified a novel HMBS gene mutation in a Chinese patient with AIP and confirmed its pathogenicity.©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.