A 6-month-old boy presents to the emergency department with fever and tachypnea, and is found to be in diabetic ketoacidosis. He has a history of intractable watery diarrhea and a gradually worsening eczematous dermatitis. His older brother had many of the same conditions, along with hypothyroidism, and died in early childhood. This likely represents a defect in _____, a key signaling molecule in __

The patient likely has IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome, characterized by early onset of Type 1 diabetes, chronic diarrhea, and an eczematous dermatitis that often proves refractory to common treatments and can continue to erythroderma. The disease is often rapidly progressive, with diverse described manifestations, including sepsis, hypogammaglobulinemia, and arthritis, and often results in death within the first years of life. These patients have defects in FoxP3 and have dysfunctional Treg cells which may switch to an inflammatory TH17 phenotype.