Felty's syndrome is a rare, potentially serious disorder that is defined by the presence of three conditions: rheumatoid arthritis (RA), an enlarged spleen (splenomegaly) and a decreased white blood cell count (neutropenia), which causes repeated infections. Although some individuals with Felty's syndrome are asymptomatic, others can develop serious and life-threatening infections. Symptoms of Felty's syndrome, in addition to those associated with the three conditions stated above, may include fatigue, fever, weight loss, discoloration of patches of skin, mild hepatomegaly (enlarged liver), lymphadenopathy (swelling of lymph nodes), Sjögren syndrome, vasculitis, lower-extremity ulcers, and other findings. The exact cause is unknown, but several risk factors have been proposed, including autoimmunity. A few familial cases of the condition have been reported. Treatment typically focuses on controlling the underlying RA; immunosuppressive therapy for RA may improve neutropenia and splenomegaly.

In another report, the authors described a family in which 3 siblings had Felty's syndrome. All of the siblings shared a specific haplotype (a group of immune system genes that may be inherited together). The authors stated that they believe this supports the theory that multiple genetic factors are involved in family members being predisposed to Felty's syndrome.

An earlier article described a family in which the mother and 2 of her 5 children had Felty's syndrome, which suggested autosomal dominant inheritance (which has not otherwise been reported).