I found out I have 1-APOE4 gene from 23 and Me a couple of years ago. My grandmother developed Alzheimers and it sounds like she had a brother who developed it at an early age. My mother died at 81 and her sister at 82. Both had good cognitive abilities and died from COPD and a Stroke from high blood pressure. My father died in his 50s from alcoholism. I don't know of anyone on his side of the family who had Alzheimers but I was estranged from his side of the family and don't know much about them.
I'm 71 and every time I forget a name, I wonder....
Take it from a 67 year old genetic "cousin" who has two copies of ApoE 4: You can forget lots of names from the last 70 or so years of your life without it being a warning bell going off. Here's why: Our memories are not etched permanently in our brain; even the ones we think are permanent are more like old home movies that we've re-watched--but edited each time we did! So names of famous people (Lincoln, JFK) and names of people (and pets) who have held important or emotionally significant roles in our lives are often remembered easily--we may even dream about them as they were decades ago! Other names, even those that we might have thought were solidly in long-term memory, can be hard to recall "on demand"--like if someone asked you "What was the name of your first grade teacher?" Free recall (sometimes called unaided recall) is far more difficult than "cued recall". That's why when we can't think of a name of that teacher, we say "Oh, she was a nun, and very petite, and sweet, and she had a name that wasn't a common name." In other words, we often remember a lot about the person, just not the name, which doesn't have any particular hook. Sometime we suddenly get it; or if you're like me, you remember the name 10 minutes after you saw the person at a store and couldn't remember her name even though you knew her job, her kids, etc. etc.
So, the kinds of memory issues that are seen in people who have subjective cognitive decline, or signs of mild cognitive impairment, are more likely to be problems with spatial memory (how do I get to the doctor's office that I have gone to for 20 years) or memory for recent events (my mother insisted she had not gone with her brother to visit an assisted living facility two days after it happened). It may also be worrying about things being "lost" or "moved " in the house because you can't remember where you put them a few days ago. Or forgetting how to do tasks you used to do easily, like keeping track of bills, or remembering what day of the week it is even after you've looked at a calendar.
It's an excellent sign that your mother (a first-degree relative) and her sister both avoided any cognitive decline--although I would talk with your doctor about any high blood pressure you have, and consider a carotid artery scan (for risk of a stroke). It's entirely possible that your maternal grandmother didn't have Alzheimer's but had either vascular dementia from coronary artery disease and/or high blood pressure or a mixed dementia with features of both vascular and Alzheimer's dementia. Your grandmother's brother may have developed multiple health issues in the 1960's or so which were tied to common practices of that time: diabetes, coronary artery disease, kidney disease from toxic exposure in farms and factories. I wouldn't assume that's relevant to you, any more than my maternal grandmother's death from a stroke at 45 has proved relevant for me.
Much better to realize that current meta-analyses of large population cohorts suggest you have about a 20-25% chance of developing either Mild Cognitive Impairment (MCI) or dementia by the age of 85. That means a 75-80% chance that you will be like your mother and aunt: live well into your 80's or beyond with a healthy brain! Having a purpose in our lives, regular social engagement (volunteering for anything from campaigns to food kitchens to reading with struggling your readers are all great options if you're looking for new outlets) and regular aerobic exercise are all great strategies. I like the view of the Stoics: We cannot control the outcome of our voyage, but we can control how we plan, and how we find joy in the journey.
I hope you continue to post, and tell us how you have stayed so healthy to age 71. We have lots of worried 30-somethings who find it hard to picture themselves our ages!