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 contributing factor for the development of HLH in the presence of other triggers. In patients in whom one is contemplating a stem cell transplant, genetic testing is useful to look for those hypomorphic alle...

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