Case Report: Late-onset primary hemophagocytic lymphohistiocytosis leading to the diagnosis of Griscelli syndrome type 2 in a young woman with phenotypically inapparent partial albinism.

Griscelli syndrome type 2 (GS-2) is a rare congenital immune dysfunction characterized by partial albinism and recurrent episodes of hemophagocytic lymphohistiocytosis (HLH). It is caused by a variant in the gene encoding Rab27a leading to a degranulation defect in melanocytes, natural killer (NK)- and T cells. Prognosis of patients with GS-2 is limited by repetitive episodes of life-threatening HLH with onset in early childhood. The only curative treatment is an allogeneic hematopoietic stem cell transplantation (HSCT). Here, we report on an 18 year old female patient with a homozygous missense p.Arg50Glnfs*35 variant in exon 2 of who presented with an exceptionally late onset of severe HLH. Her phenotypically inapparent albinism complicated to correctly diagnose GS-2. Immune function assays confirmed a T- and NK cell degranulation deficiency characteristic for patients with primary HLH, while microscopic hair analysis revealed melanin clumps secondary to melanocyte functional impairment. To understand why disease onset occurred unusually late in this patient, we investigated the patient's T cell and polymorphonuclear neutrophil (PMN) function in more detail. We could show that intracellular granzyme B storage in cytotoxic T cells was increased compared to healthy donors and that the patient's T cells maintained some degranulation activity. Both, antigen-specific cytotoxic response and proliferation capacity of the patient's T cells were preserved. We demonstrate for the first time that also PMN degranulation, assessed as stimulation-induced CD66b and CD11b cell membrane expression, is dysfunctional in patients with Rab27a deficiency-associated primary HLH. The patient was treated with steroids and cyclosporine A for immunosuppression to control the HLH. After two severe episodes within only a few months, she eventually received an allogeneic HSCT and has not experienced further HLH episodes for now more than 3 years after the HSCT procedure. This case should raise awareness for the possibility of initial manifestation of primary, genetically-determined HLH even in adult patients.