Hemophagocytic lymphohistiocytosis as the initial manifestation of bone marrow failure in a child with a TERC variant telomere biology disorder.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening systemic hyperinflammatory syndrome, rarely associated with bone marrow failure (BMF). Telomere biology disorders (TBD) are caused by inherited defects in telomerase processes and can have heterogeneous presentations including idiopathic pulmonary fibrosis, cirrhosis, and BMF. We report a case of a 10-year-old male from Lima, Peru, who presented with HLH as the initial manifestation of a TBD. He experienced fever, gastrointestinal symptoms, and mucocutaneous involvement. Initial laboratory analyses revealed pancytopenia and elevated inflammatory markers. Despite symptomatic and antibiotic treatment, his clinical condition persisted leading to a suspicion of Kawasaki disease and, subsequently, HLH. Immunomodulatory treatment was initiated with a good clinical response. Bone marrow aspiration revealed severe hypocellular bone marrow and cytophagocytosis. Genetic studies identified a pathogenic variant in the TERC gene (n.110_113del), which was also found in the patient's mother and brother. HLH as the initial manifestation of BMF is rare. This case highlights the importance of considering TBD in children with BMF of unclear etiology and the value of genetic testing in such cases.