The Meanings of Grenz
Back in the early 1700's Grentz and Grenz were both used as well as other variations. As of now I do not know which pre-dates which. Surnames were first used in Germany during the 12th century however there were often many variations in spellings. Surnames did not become more standardized until the 16th century. A direct translation of Grenz is border, borderline or boundary, perhaps indicating that the first users of Grenz lived on or near a border, boundary, or frontier of some kind. Watching an early TV show of Mission Impossible I noticed on a fence "Grenz Verboten" - Border - Forbidden.
During the Napoleonic Wars in the mid 1800's the name Grenz pops in use in the context of armies. Such as: Brooder Grenz infantry and the 1st Banal-Grenz Regiment denoting type of unit as being frontier.
Grenz is also used in the medical field.
Grenz Rays are defined as: Very soft x-rays, closely allied to ultraviolet rays in their wavelength and in their biological action upon tissues. (The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company.)Grenz Zones: in histopathology, a narrow layer beneath the epidermis that is not infiltrated or involved in the same way as are the lower layers of the dermis.