BRCA1 and heredity

[Silly Green Monkey]

In all my googlings, which was hampered by constantly forgetting the most efficient terms, it's strictly a 50/50 chance that a child of a carrier would inherit. However, when my mother and I attended the same college, we went to a hereditary-cancer talk+lunch and they wanted a volunteer for a family tree. I volunteered, but when I kept asking Mom for the answers to the questions, the lecturer switched to her. Just about everyone in her family tree, to the man, had cancer. Her father had brain cancer, but her mother's brothers had cancers indicating they also carried the mutation. My sister didn't inherit, but she seems to be extremely rare in that respect, going from Mom's side of the family. How can that be reconciled with only a half chance of inheriting? Is there something else that would make children with the mutation better survive? Or, is my family simply on the high side of randomness?

 

[Planigale]

In all my googlings, which was hampered by constantly forgetting the most efficient terms, it's strictly a 50/50 chance that a child of a carrier would inherit. However, when my mother and I attended the same college, we went to a hereditary-cancer talk+lunch and they wanted a volunteer for a family tree. I volunteered, but when I kept asking Mom for the answers to the questions, the lecturer switched to her. Just about everyone in her family tree, to the man, had cancer. Her father had brain cancer, but her mother's brothers had cancers indicating they also carried the mutation. My sister didn't inherit, but she seems to be extremely rare in that respect, going from Mom's side of the family. How can that be reconciled with only a half chance of inheriting? Is there something else that would make children with the mutation better survive? Or, is my family simply on the high side of randomness?

BRCA does increase the risks of breast, prostate and pancreatic cancer for those assigned male sex at birth, in addition to the risks for those AFAB. Obviously cancer is a common cause of death and occurs in those without BRCA genes, so the BRCA gene adds risk. There are other genes that may be in the family that increase risk for other cancers or there may be more than one BRCA gene lineage in the family, certain ethnic groups may have high prevalence of BRCA so marrying within your ethnic group amy mean there is more than one source for a familial BRCA gene. You cannot attribute all cancers to BRCA. If you are concerned you could ask for referral to a clinical genetics unit, after you have obtained a detailed family tree with history of cancers and age of onset.

 

[Silly Green Monkey]

I did suspect some bit of inbreeding possible, her family were farmers in Delaware in the early 1900s and a 'family friend' also had breast cancer fairly young. It's more that I noticed in the family tree, almost every single family member seemed to have been impacted by the gene, as though it was inherited closer to 100% of the time instead of 50%. I did learn that it's possible to inherit two broken copies and still survive, which was a surprise. I'm more glad that she joined the Army and met my father, breeding well outside her local gene pool.