Acute Intermittent Porphyria: Complete Phenotype in a Patient with p.Arg173Trp Variant in Thailand

Objective: Rare diseaseBackground: Acute intermittent porphyria (AIP) is a rare genetic disease caused by the deficiency of porphobilinogen deam-inase enzyme in the heme synthesis pathway. AIP is passed by autosomal dominant inheritance. Heterozygous pathogenic variants in hydroxymethylbilane synthase (HMBS) are associated with AIP. Multisystemic manifes-tations of acute neurovisceral features exist, which are quite challenging for diagnosis. Currently, few patients worldwide have been reported with AIP. A small number of reports have been published in Thailand, but none have been confirmed by molecular genetics diagnosis.Case Report: A 14-year-old female adolescent presented with severe intermittent abdominal pain, vomiting, seizure, poste-rior reversible encephalopathy syndrome, syndrome of inappropriate antidiuretic hormone, and muscle weak-ness, which are all classic phenotypes of an acute AIP attack. The patient received several investigations be-fore AIP was suspected. High levels of urine porphobilinogen, high levels of urine aminolevulinic acid, and a heterozygous known pathogenic variant in HMBS: c.517C>T (p.Arg173Trp) were identified. Therefore, AIP was the definitive diagnosis. Then, Sanger sequencing testing was performed for the patient's family; this variant was found in her father, paternal grandmother, and sister, who were all asymptomatic (latent AIP). After the AIP was confirmed, high carbohydrate loading was given as a standard treatment. She had a full recovery; her clinical course of the attack episode lasted for 8 weeks.Conclusions: An early diagnosis of AIP leads to prompt and specific treatment, which can shorten the duration of attacks, prevent complications, reduce the cost of treatment, and reduce the mortality rate.