Key diagnostic markers for autoimmune lymphoproliferative syndrome with molecular genetic diagnosis.

Autoimmune lymphoproliferative syndrome (ALPS) is a rare immunodeficiency caused by mutations in genes affecting the extrinsic apoptotic pathway (FAS, FASL, CASP10). This study evaluated the clinical manifestations, laboratory findings, and molecular genetic results of 215 patients referred as possibly having ALPS. Double-negative T-cell (DNT) percentage and in vitro apoptosis functional tests were evaluated by fluorescence-activated cell sorting; interleukin 10 (IL-10) and IL-18 and soluble FAS ligand (sFASL) were measured by enzyme-linked immunosorbent assay. Genetic analysis was performed by next-generation sequencing. Clinical background data were collected from patients' records. Patients were categorized into definite, suspected, or unlikely ALPS groups, and laboratory parameters were compared among these groups. Of 215 patients, 38 met the criteria for definite ALPS and 17 for suspected ALPS. The definite and suspected ALPS patient populations showed higher DNT percentages than unlikely ALPS and had higher rates of lymphoproliferation. Definite ALPS patients had a significantly more abnormal in vitro apoptosis function, with lower annexin, than patients with suspected ALPS (P = .002) and patients not meeting ALPS criteria (P < .001). The combination of elevated DNTs and an abnormal in vitro apoptosis functional test was the most useful in identifying all types of ALPS patients; the combination of an abnormal in vitro apoptosis functional test and elevated sFASLs was a predictive marker for ALPS-FAS group identification. Lymphoproliferation, apoptosis functional test, and DNTs are the most sensitive markers; elevated IL-10 and IL-18 are additional indicators for ALPS. The combination of elevated sFASLs and abnormal apoptosis function was the most valuable prognosticator for patients with FAS mutations.