Recently the information at the Washington University Neuromuscular Disease Centre for HNPP has been updated to include the KARS mutation HNPP phenotype. KARS mutations according to this info seem produce two distinct phenotypes, a recessive intermediate CMT type, and a dominant HNPP type.
There is more info available on this at the OMIM website, but not very much about the HNPP type.
The vast majority of those with HNPP have the common PMP22 deletion on chromosome 17. A small number of cases are diagnosed as having HNPP by clinical testing and family history, but do not have the common pmp22 deletion, or the few known small point mutations of pmp22 which generally cause a more severe HMSN.
I have been unable to find out whether a genetic test exists for the KARS mutation, it maybe that it isn’t publicly available yet.