Chronic granulomatous disease (CGD) is an inherited (genetic) immune system disorder that occurs when a type of white blood cell (phagocyte) that usually helps your body fight infections doesn't work properly. As a result, the phagocytes can't protect your body from bacterial and fungal infections.
The house was built circa 1939. When used in date ranges, a circa is applied before each approximate date, while dates without a circa immediately preceding them are generally assumed to be known with certainty.
Presumably this is when the Greek Revival house was built. But that's not to say that there wasn't a house on the property, perhaps in the same strategic hilltop location, before 1848. It just means that this particular house most likely dates to that time.