Unveiling the Uncommon: A Unique Case of ALPS-like Syndrome Complicated by Plasma Cell Disorder.

Multiple myeloma is a rare disease in pediatrics, where about 30 cases are described under 15 years old. It is even rarer when atypical multiple myeloma occurs in the context of autoimmunity. This case describes a 9-year-old female with autoimmune lymphoproliferative-like disease and combined immune deficiency that developed acute kidney failure with monoclonal peak associated with RAC2 and TNFRSF9 variants. An adapted protocol from the backbone adult multiple myeloma standard of care with the addition of an allogeneic hematopoietic stem cell transplant was used. The patient, now nearly a year posttransplant, shows 100% chimerism with no sign of relapse.