Nakajo-Nishimura syndrome: A Patient Guide

Nakajo-Nishimura syndrome (NNS) is a very rare, genetic condition characterized by a persistent and dysregulated immune response that affects the entire body ^[1]. It belongs to a group of diseases known as autoinflammatory syndromes, where there is an inappropriate activation of the innate immune system, often without an infection or autoantibodies ^[2]. Historically identified in Japan but now recognized in patients worldwide, NNS typically begins in early childhood with recurring fevers and distinct skin rashes that can look like red, tender nodules or cold-induced patches ^[1][3].

The condition is progressive, meaning its physical effects often change as a person grows. A hallmark of NNS is the gradual loss of body fat and muscle, particularly in the face and upper body, which can lead to a very thin appearance ^[1]. Over time, chronic inflammation can also cause the joints—especially in the fingers and hands—to become stiff or fixed in bent positions, a process known as joint contractures ^[3]. Because the disease affects the whole body, it may also involve internal organs and, in some cases, the brain and kidneys ^[1][4].

At the biological level, classic NNS is caused by mutations in the PSMB8 gene, which helps build the immunoproteasome, the cell’s internal mechanism responsible for processing proteins ^[5]. When this function is impaired, it causes cellular stress and triggers a strong inflammatory signaling response driven by a chemical called type I interferon ^[6]. This state of chronic immune activation is why NNS is classified under the broader “umbrella” of PRAAS (Proteasome-Associated Autoinflammatory Syndromes), a spectrum that includes related conditions like CANDLE and JMP syndromes ^[1][7].

While living with NNS requires lifelong management and careful monitoring, the medical landscape is evolving ^[8]. Emerging therapies, such as JAK inhibitors, are sometimes used off-label by specialists to quiet the interferon pathway ^[9][10]. These medications aim to reduce active symptoms like fevers and rashes, though they carry significant immunosuppressive risks and may not reverse established changes like fat loss or joint contractures. By working with a specialized medical team and staying consistent with symptom management, families and patients can take proactive steps to protect long-term health and mobility ^[8].