AUTHOR=Gu Hao , Chen Zhenping , Ma Jie , Ma Jingyao , Fu Lingling , Zhang Rui , Wang Tianyou , Wu Runhui TITLE=Case report: Effectiveness of sirolimus in a de novo FAS mutation leading to autoimmune lymphoproliferative syndrome-FAS and elevated DNT/Treg ratio JOURNAL=Frontiers in Pediatrics VOLUME=10 YEAR=2022 URL=https://www.frontiersin.org/journals/pediatrics/articles/10.3389/fped.2022.868193 DOI=10.3389/fped.2022.868193 ISSN=2296-2360 ABSTRACT=Background

The autoimmune lymphoproliferative syndrome (ALPS) is a rare disease characterized by defective function of the FAS death receptor, which results in chronic, non-malignant lymphoproliferation and autoimmunity accompanied by elevated numbers of double-negative (DN) T cells (T-cell receptor α/β + CD4–CD8–) and an increased risk of developing malignancies later in life.

Case description

Here, we report a patient with a de novo FAS mutation with a severe phenotype of ALPS-FAS. The FAS gene identified as a novel spontaneous germline heterozygous missense mutation (c.857G > A, p.G286E) in exon 9, causing an amino acid exchange and difference in hydrogen bond formation. Consequently, the treatment with sirolimus was initiated. Subsequently, the patient’s clinical condition improved rapidly. Moreover, DNT ratio continuously decreased during sirolimus application.

Conclusion

We described a novel germline FAS mutation (c.857G > A, p.G286E) associated with a severe clinical phenotype of ALPS-FAS. Sirolimus effectively improved the patient clinical manifestations with obvious reduction of the DNT ratio.