The Lens, the Limb, and the Clot: An Atypical Paediatric Presentation of Homocystinuria

Aim: To highlight a rare presentation of homocystinuria in a pediatric patient, initially manifesting as venous thrombosis, and later diagnosed through multidisciplinary evaluation of systemic features. Case Presentation: A 10-year-old boy, born to third-degree consanguineous parents, presented with progressive right lower limb swelling, later involving the left limb. Doppler ultrasonography revealed thrombosis of the infrarenal inferior vena cava extending into the bilateral common and right external iliac veins, for which anticoagulation was initiated. There was no history of fever, trauma, or systemic illness. Two years later, he developed seizures. On examination, he was disoriented, with a tall stature (165 cm) and increased arm span (170 cm). Ophthalmologic evaluation revealed ectopia lentis of the left eye. In view of multisystem involvement—thrombosis, seizures, marfanoid habitus, and lens dislocation—homocystinuria was suspected. Serum homocysteine levels were markedly elevated, and genetic testing confirmed a pathogenic variant consistent with the diagnosis. Multidisciplinary management involving neurology and hematology teams was initiated. The patient has remained clinically stable and is under regular follow-up for the past three years. Conclusion: This case emphasizes the need to consider metabolic disorders such as homocystinuria in children with unexplained thrombotic and neurological symptoms. A high index of suspicion, combined with coordinated multidisciplinary care, is crucial for early diagnosis and improved long-term outcomes.