TAP deficiency syndrome
Bare lymphocyte syndrome (BLS) is characterized by a severe down-regulation of HLA class I and/or class II molecules. In type 1 BLS the defect is confined to HLA class I molecules, while in type 2 BLS HLA class II molecules are down-regulated [1]. Characterization of 22 patients with type 1 BLS over the last 22 years has revealed the existence of several clinically and immunologically distinct disease subsets [1–20]. In this review we will focus on a recently characterized group of patients with a distinct disease phenotype due to a defective TAP complex, the peptide transporter complex associated with antigen presentation [2–15]. We will describe clinical manifestations and immunological findings of patients suffering from TAP deficiency syndrome, and discuss the differential diagnosis and therapeutic options.