VHL - is it rare?

 My pal's brother has had to have emergency surgery - hemangioblastoma in his cerebellum. They have suggested he gets tested for VHL.

Small genetic world. 

His father is unknown - he is probably the carrier- too long a go to have been my brother. My pal's half brother. 

My brother was always told he couldn't be reckless. 

He never was, we think. 

Imagine if he was, a niece or nephew.