What are the genetic changes related to spondyloenchondrodysplasia with immune dysregulation ?
Mutations in the ACP5 gene cause SPENCDI. This gene provides instructions for making an enzyme called tartrate-resistant acid phosphatase type 5 (TRAP). The TRAP enzyme primarily regulates the activity of a protein called osteopontin, which is produced in bone cells called osteoclasts and in immune cells. Osteopontin performs a variety of functions in these cells.  Osteoclasts are specialized cells that break down and remove (resorb) bone tissue that is no longer needed. These cells are involved in bone remodeling, which is a normal process that replaces old bone tissue with new bone. During bone remodeling, osteopontin is turned on (activated), allowing osteoclasts to attach (bind) to bones. When the breakdown of bone is complete, TRAP turns off (inactivates) osteopontin, causing the osteoclasts to release themselves from bone.  In immune system cells, osteopontin helps fight infection by promoting inflammation, regulating immune cell activity, and turning on various immune system cells that are necessary to fight off foreign invaders. As in bone cells, the TRAP enzyme inactivates osteopontin in immune cells when it is no longer needed.  The ACP5 gene mutations that cause SPENCDI impair or eliminate TRAP's ability to inactivate osteopontin. As a result, osteopontin is abnormally active, prolonging bone breakdown by osteoclasts and triggering abnormal inflammation and immune responses by immune cells. In people with SPENCDI, increased bone remodeling contributes to the skeletal abnormalities, including irregularly shaped bones and short stature. An overactive immune system leads to increased susceptibility to autoimmune disorders and impairs the body's normal immune response to harmful invaders, resulting in frequent infections. The mechanism that leads to the other features of SPENCDI, including movement disorders and intellectual disability, is currently unknown.