Hi everyone,
My niece has recently been diagnosed with underactive thyroid. I have Hashimoto's and my mum has underactive thyroid too (not sure if she's had antibody tests or confirmed Hashimoto's). Could it be that my sister has Hashimoto's too (my niece's mum). Or can Hashimoto's skip generations?
Thanks xx
"Can Hashimoto's skip generations"
My limited understanding is that it doesn't work like that. This is how the Genetic and Rare Diseases Information Centre describes it:
Hashimoto's syndrome is an autoimmune disorder thought to result from a combination of genetic and environmental factors. Some of these factors have been identified, but many remain unknown. People with Hashimoto’s syndrome have antibodies to various thyroid antigens.
Several genes appear to be possible risk factors for Hashimoto syndrome, such as the gene family called the human leukocyte antigen (HLA) complex, which helps the immune system distinguish the body's own proteins from proteins made by viruses and bacteria or other agents. It is also more common in people who have other family members with the disease. However, the genetic factors have only a small effect on a person's overall risk of developing this syndrome. Non-genetic factors that may trigger the syndrome in people at risk may include changes in sex hormones (particularly in women), viral infections, high cholesterol, vitamin D deficiency, certain medications, exposure to ionizing radiation, and excess consumption of iodine. Hashimoto’s syndrome is associated with other autoimmune diseases, including connective tissue diseases, joint diseases (such as autoimmune types of arthritis), pernicious anemia, adrenal insufficiency, celiac disease, and type 1 diabetes mellitus. Also, people with autoimmune diseases seem to have a higher risk of developing Hashimoto's syndrome.
Thank you for replying so quickly MaisieGray. My head is a bit foggy at the moment. So do you think this means that my sister may be carrying the gene for Hashimoto's but that it may not have been triggered in her, but passed down to my niece where it has been triggered?
Well no, because the disease itself is not inherited, or perhaps more accurately, the inheritance pattern of Hashimoto thyroiditis is unclear because as stated above, many genetic and environmental factors appear to be involved. Instead, what's known for sure is that it can tend to "run" or "cluster" in families, but when that clustering happens, it can arise from different factors in different disorders - some disorders that affect multiple family members are caused by gene mutations, which can be passed down from parent to child, whilst other conditions that appear to run in families are not caused by mutations in single genes. Instead, environmental factors such as dietary habits or a combination of genetic and environmental factors are responsible for them. What is obviously known about Hashimoto's is that having a close relative with autoimmune thyroiditis or another autoimmune disorder likely increases a person's risk of developing the condition.
Autoimmune disease can skip generations, so a grandfather and grandson can both develop one, while the parent probably has the capacity to develop it, they just don't. Your sister is probably capable of developing hashimotos, it's just it hasn't triggered in her (yet?). We really need to understand what triggers autoimmune disease in some and not others!
My understanding of Hashi’s is that it’s not hereditary. There’s not a faulty gene as such to be passed down. Although it is known that for many there does seem to be a higher risk of close members of ones family do have it. Certainly seems to ‘run’ in my family, grandmother, mum, and my sister (although she’s the only one with Graves) Maybe it’s just a predisposition to, a weakness if you like which may or may not be triggered.
Thank you everyone this is very helpful 
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