Abstract
RATIONALE: This study presents a case of hemoglobin M disease (HMD), a rare inherited disorder characterized by persistent cyanosis and hypoxemia, observed across 3 generations within a single family. The diagnosis of HMD poses significant challenges, particularly in asymptomatic individuals, due to its rarity and the subtlety of its symptoms. Notably, there is a scarcity of reports on methemoglobinemia in pediatric populations, which further complicates early detection and intervention. The primary objectives of this study are to enhance awareness of HMD, to advocate for accurate diagnosis and timely treatment, and to underscore the necessity of considering this condition in patients with a familial history of cyanosis. PATIENT CONCERNS: A 6-year-old boy presented to our hospital with fatigue and cyanosis in his lips and mouth. Both the child's mother and grandfather had a history of similar symptoms since their childhood. DIAGNOSES: Diagnosis of hemoglobin M disease. INTERVENTIONS: The patient was treated with vitamin C. OUTCOMES: Genetic testing revealed that the patient and her mother carried the c.190C > T mutation, leading to the p.H63Y amino acid change linked to the methemoglobin (MetHb) mutation. Despite undergoing vitamin C therapy, the patient's symptoms of cyanosis and fatigue persisted. LESSONS: Hemoglobin M disease can be readily diagnosed with a delay. Methemoglobinemia should be considered in patients with a family history of cyanosis but no cardiopulmonary disease. Hospital blood gas analysis should include a protocol for detecting methemoglobin, and genetic testing can help confirm the diagnosis.