Nails and black stripe

I met a person who spoke and showed that he has had a black stripe on his toenail since birth.

I saw that indeed the toenail had an almost black stripe, longitudinally, towards the tip of the toe.

One of his relatives had not had such a black stripe since birth, but had developed at a young age and permanently.

The story became even more interesting, as family members also had a black stripe on their toenails.

I know that nails are basically body feces, but also a good source of information about his condition and gait.

It is not a common disease or the like. What could this mean from an astrological point of view?