eli5 – what determines disability?


i mean no harm in this question, i’m simply curious as my sister suffers from muscular dystrophy and have always been curious why, genetically, she was dealt such a bad card? at what point in pregnancy do genetics determine our fate?

In: 1

Your genome is decided the moment an egg is fertilized. What the exact nature of the defect is depends on the particular disease (or more accurately, the other way around).

Genetics determine our fate at the moment of conception, when a particular sperm cell fertilizes a particular egg cell. If the process results in some faulty genes, then that’s how it’s going to be.

That said, genetics isn’t always a sentence. More often than not genetics simply means that the person with these genes is more likely to get some particular condition than the average person. Like, say, on average 5% of people get diabetes at some point in their lives, but the genetics of this particular person make the probability of getting diabetes 20% for them specifically (I’m making numbers up here).

It varies from disability to disability.
Your sister’s disability is one that we understand the causes of the best.
Your sister’s muscular dystrophy is definitely genetic in origin.

It is possible (though unlikely) that your sister’s muscular dystrophy came from a mutation.
Your mother’s egg or your father’s sperm could have contained a mutated gene, or your sister’s zygote could have introduced a mutation very early on when your sister was just a couple cells.

But the majority of muscular dystrophy cases aren’t due to mutations.
They’re due to (maybe recessive) genes that your mother’s side and your father’s side just coincidentally happened to be carrying, and just coincidentally happened to be in the egg and sperm that made your sister.
In that sense you could argue your sister’s fate was decided before she was even conceived.

I understand that this is tagged with ‘biology’ but wanted to add a little input as someone who works with people with disabilities and thought this could help with awareness.

In the UK someone is considered to have a Learning disability if they’re IQ is less than 70. That is the criteria. There is also a written/mathematical/cognitive assessment to support this.

While a ‘learning difficulty’ is something that can affect your ability to learn. Specific examples are dyslexia, ADHD.

America call what British people call a learning difficulty, a ‘learning disability’.

British people then use the term learning disability to diagnoses cognitive impairment, I.e. IQ < 70, while America call it an ‘intellectual disability’ or a global intellectual deficiency. Confusing right?

Autism, Down syndrome, are learning disability- associated conditions but are in fact not a learning disability.

Similarly, muscular dystrophy is in itself, not a physical disability, it is a disease, that causes impairments that can effect the physical functioning of a person, for long-term, which makes it a physical disability. Some people can have a brain injury that constitutes a physical disability, others with the same type of injury can have no physical disability!

I hope people find this insightful as I do.. it’s a super common misconception!