H Syndrome, a Non-Langerhans Cell Histiocytosis to Know: A Case Report

Abstract

Background: H syndrome is a rare autosomal recessive, multisystem non-Langerhans cell histiocytosis associated with biallelic pathogenic variants in SLC29A3. Published data from North Africa remain limited, and phenotypic variability may complicate clinical recognition. Case Presentation: A 24-year-old Moroccan man, born to non-consanguineous parents, presented with an eight-year history of progressive hyperpigmented sclerotic skin thickening and bilateral lower-limb oedema. He had type 1 diabetes mellitus from the age of 7 years. Examination demonstrated extensive, bilaterally symmetrical hyperpigmented sclerotic plaques with hypertrichosis involving the limbs, trunk, abdomen, and lower back, with characteristic sparing of the knees and popliteal fossae. Additional findings included exophthalmos, corneal arcus, diabetic retinopathy, bilateral knee and ankle swelling, hallux valgus, flat feet, and hepatomegaly. Hormonal investigations were normal, while serum protein electrophoresis showed a chronic inflammatory profile. Skin biopsy demonstrated dermal fibrosis with histiocytic infiltration, and genetic testing confirmed a biallelic pathogenic SLC29A3 variant. Discussion: The combination of characteristic cutaneous distribution and childhood-onset insulin-dependent diabetes supported the clinical suspicion of H syndrome despite overlap with other sclerosing and histiocytic disorders. Conclusion: Recognition of this distinctive clinical pattern may facilitate appropriate molecular confirmation, genetic counselling, and multidisciplinary management, particularly in populations for which published H syndrome data remain scarce.