Should testing for genetic causes of HLH be performed in all patients with MAS or secondary HLH regardless of the patient's age?  

Familial HLH (fHLH) is a pediatric disease. Therefore, there is no place for genetic testing to establish a diagnosis of fHLH in adults, and treatment for HLH should not be delayed while waiting for genetic testing. However, there are hypomorphic polymorphisms in the fHLH genes that may be a contrib...

I agree genetic HLH is a pediatric disease but one cannot await a genetic answer.