Will heredomacular dystrophy cause other severe illnesses apart from the difficulty in reading?

Hi doctor,

My fiancee has a problem with heredomacular dystrophy, and he is 30 years old. At this age, he does not have many problems. Actually, this disease has been present from the time of birth but was diagnosed ten years ago when he felt he finds difficulty reading very small words. Otherwise, he easily drives a car and does many other daily routine works. His mother is also having a problem. She is now around 53 years of age, and she is also having this problem since birth. She also, at this age, does not have so many problems. They both have faced one common thing, which is reading small words and very small words. I searched on the internet and found many things which scared me. My concern is that if this increase, what is the possible impact of this on him? And if this possibility his dystrophy progress or remains like his mother with no more impact. Or does this disease turns to other terrible diseases like RPE and other diseases? This scares me a lot. Kindly guide me about his problem so that I can make a firm decision about my life.