Table 1 Summary of the terms related to normal pressure hydrocephalus (NPH) and the different groups described in the paper

Idiopathic normal pressure hydrocephalus (iNPH)

The idiopathic form of NPH in general (includes both familial and sporadic subgroups)

Familial idiopathic normal pressure hydrocephalus (fNPH)

The familial form of iNPH. An iNPH patient was referred to as a fNPH patient if there were multiple iNPH (fNPH) cases in the family (the precise criteria are described in “Methods” section)

Sporadic idiopathic normal pressure hydrocephalus

An iNPH patient does not have any relatives with iNPH

Secondary normal pressure hydrocephalus (sNPH)

NPH caused by a known (acquired) cause, e.g. subarachnoid hemorrhage, brain tumor, traumatic brain injury etc.

Non-iNPH relatives

In this paper, the probable fNPH patients’ ≥ 60-year-old relatives that had no iNPH (fNPH)