Rare missense variants in the ALPK1 gene may predispose to periodic fever, aphthous stomatitis, pharyngitis and adenitis (PFAPA) syndrome

PFAPA is an autoinflammatory syndrome characterized by periodic fever, aphthous stomatitis, sterile pharingitis, and adenitis, with an onset usually before the age of five. While the condition is most commonly sporadic, a few cases are familial and are usually compatible with an autosomal dominant (AD) transmission pattern, with reduced penetrance in some pedigrees. We performed exome analysis in a family where PFAPA was present in three relatives in two generations showing apparent AD segregation, identifying several rare and/or novel heterozygous variants in genes involved in the autoinflammatory pathway. Following segregation analysis of candidate variants, only one, c. 2770T>C p.(S924P) in the ALPK1 gene, was found to be consistently present in affected family members. ALPK1 is broadly expressed in different tissues and its protein is the intracellular kinase activated by the bacterial ADP-heptose bisphosphate that phosphorylates and activates TRAF-Interacting protein with Forkhead-Associated domain (TIFA) and triggers the immediate response to Gram-negative bacterial invasion. Sequencing analysis of 13 additional sporadic cases and 10 familial PFAPA cases identified two additional heterozygous missense variants c.1024G>C p.(D342H) and c.710C>T p.(T237M) in two sporadic patients, suggesting that rare variants in ALPK1 may represent a predisposing factor for recurrent periodic fever in a pediatric population.