A progressive neurological condition with acquired sea-blue histiocytosis further the diagnosis of Niemann-Pick type C1 in a 10-year-old boy.

Sea-blue histiocytes in bone marrow can be associated with a number of conditions and have indeed often been reported in Niemann-Pick diseases, mostly in Niemann-Pick type B, but also Niemann-Pick type C. Rarely, it was reported to be related to a progressive neurological condition. In this work, early bone marrow aspirations in a boy following the discovery of hepatosplenomegaly at 1 month of age and later isolated splenomegaly did not reveal abnormal cells (which is not uncommon). Numerous sea-blue histiocytes were found in a repeated exam when the child was 10-year old, at a time he had developed a progressive neurological condition with frequent falls, clumsiness, slow and slurred speech, intellectual disability, dystonic movements, and dysphagia. Acquired sea-blue histiocytes should be considered initially on the basis of clinical symptoms. Whole-exome sequencing identified two variants in the NPC1 gene, leading to the diagnosis of Niemann-Pick type C1. This case points out the presence of sea-blue histiocytes in the bone marrow and has helped to reach a diagnosis of NPC1 which was very difficult to establish even after years of study. Given the rarity of this pathology and the variety of clinical presentations, it is important to communicate the possible forms of presentation of this syndrome.