Abstract: Primary hypertrophic osteoarthropathy (PHO) is a rare autosomal recessive hereditary disease classified into two subtypes, PHOAR1 and PHOAR2. PHOAR2 is caused by mutations in the SLCO2A1 gene, and patients often present with atypical gastrointestinal manifestations such as chronic diarrhoea, which easily leads to misdiagnosis. This paper presents a 22-year-old male patient who suffered from recurrent abdominal pain, loose stools and tarry stools for six years; symptomatic treatments administered repeatedly by the gastroenterology department only achieved transient relief. Symmetric digital clubbing gradually developed five years after disease onset, and the patient presented to hospital with aggravated diarrhoea in the latest half year. Nail histopathology revealed dermal mucinous degeneration. Gastrointestinal endoscopy showed chronic non-atrophic gastritis and proctitis combined with positive Helicobacter pylori infection. Whole-exome sequencing identified a pathogenic splice-site variant (c.941-1G＞A) in the SLCO2A1 gene, confirming the diagnosis of PHOAR2-type primary hypertrophic osteoarthropathy.

Key words: primary hypertrophic osteoarthropathy, chronic diarrhea, SLCO2A1, digital clubbing, genetic diagnosis