Identifying Biomarkers in the Autoimmune Lymphoproliferative Syndrome (ALPS): IL-18, TNF-á, Serum Vitamin B12, Soluble FasL, and Plasma IL-10 Levels Are Useful Adjuvant Diagnostic Tools.

The autoimmune lymphoproliferative syndrome (ALPS) is a genetic disorder of lymphocyte apoptosis. Clinical findings include lymphadenopathy, splenomegaly, multi-lineage cytopenias, hypergammaglobulinemia and an increased risk for lymphoid malignancies. Nearly 65 % of ALPS patients have a heterozygous mutation in the TNFRSF6 gene coding for the FAS protein. Recently, analysis of selected biomarkers in a smaller group of ALPS patients has been reported (Blood.2009Mar26;113(13):3027-30). However, there is currently no algorithm to predict the presence or absence of TNFRSF6 (FAS) mutations in patients with clinical symptoms of ALPS.

We studied 562 individuals among ALPS patients and their relatives evaluated at the NIH under an IRB approved ALPS natural history protocol. We included 166 ALPS patients with defined germline or somatic FAS mutations, 5 patients with other genetic defects affecting FAS mediated apoptosis, 92 ALPS patients with unknown genetic defects (ALPS Type III), 120 FAS mutation-bearing healthy relatives and 179 mutation-negative healthy relatives as controls. Plasma levels of 15 different cytokines and soluble FAS ligand (sFASL) were measured for all groups. In addition, peripheral blood immunophenotyping data and serum vitamin B12 (B12) results from patients and controls were reviewed. For statistical calculations we used Wilcoxon-Mann-Whitney test. We also measured likelihood ratios (LR+ = sensitivity/100-specificity; LR- = 100-sensitivity/specificity) and probabilities ((odd / 1+odd) X 100) for the relevant biomarkers.

As compared to controls, ALPS Ia patients with either germline or somatic FAS mutations demonstrated significantly higher serum vitamin B12 (p<0.0001), sFASL (p<0.0001), IL-10 (p<0.0001), IL-18 (p<0.0001) and TNF-alpha (p<0.001) levels. Those markers were also elevated in ALPS III patients but on a much less remarkable fashion. As previously described, there were a significantly decreased percentage of memory (CD20+CD27+) B cells (p<0.0001) in all ALPS groups. Moreover, a ratio of CD20+CD27+ to CD20+ cells > 0.16 (16%) made the diagnosis of ALPS unlikely (LR=0.17). We also found that patients with a combination of DNT>4% and with IL10 >40pg/ml or B12 >1500ng/L or sFASL >300pg/ml have a 97% chance of harboring a FAS mutation. Conversely, ALPS patients with DNTs <2% combined with sFASL <200pg/ml carry only 1.7% chance of having a FAS mutation.

The combination of elevated DNT counts with increased sFASL, vitamin B12 or IL10 levels in blood is strongly linked to the presence or absence of a FAS mutation. Also, TNF-alpha and IL-18 are novel markers associated with ALPS. This enables the targeting of patients with clinical features of ALPS to have a more directed evaluation particularly in regard to DNA sequencing for FAS mutations.

No relevant conflicts of interest to declare.