A Novel Cause of CIDP: Homozygous Hotspot Mutation, c.793 C > T in CASP8 Gene

Caspase-8 enzyme deficiency (CED) is a rare autosomal recessive inborn error of immunity with autoimmune lymphoproliferative syndromes (ALPS), deficient extrinsic apoptosis and hyperactivation of the mammalian target of rapamycin (mTOR) pathway.

Features of our patient with early onset chronic inflammatory demyelinating polyneuropathy (CIDP) are presented in detail. We report features of ALPS due to CED (ALPS-CED) in 6 patients in previous literature and our patient with the homozygous hotspot mutation, c.793 C > T in the CASP8 gene, and demonstrate that such mutation is a novel cause of CIDP.

Our patient fits the spectrum of genetic disorders causing ALPS with dysregulation of the mTOR pathway. Autoimmune lymphoproliferative syndrome with FAS mutations (ALPS-FAS) is also associated with hyperactivation of the mTOR pathway but hematologic symptoms are more severe than ALPS-CED. Both ALPS-FAS and ALPS-CED lead to autoimmunity and improve with use of mTOR inhibitors. ALPS-FAS is characterized by the elevation of alpha beta-double negative T-cells (DNT) and hypergammaglobulinemia, while such features are not prominent in ALPS-CED. Patients with ALPS-CED not only suffer from ALPS but also present with an immune deficiency and a chronic inflammatory state both related to non-apoptotic functions of caspase-8.

Both ALPS-FAS and ALPS-CED are characterized by deficient extrinsic apoptosis and dysregulation of the mTOR pathway. Compared to ALPS-FAS, the phenotype of ALPS-CED is more complex due to a more diffuse dysfunction of the non-apoptotic pathways. To our knowledge, early onset CIDP in a patient with homozygous hotspot mutation, c.793 C > T in CASP8, has not been reported previously.