X-Linked Genetic Intellectual Disability #AtoZChallenge

Posted on by Astrid

Hi everyone. I can’t remember whether, in my post on the genetics of intellectual disability, I mentioned the difference between autosomal and X-linked genetic causes of intellectual disability. Autosomally genetic conditions are those that are present on one of the autosomes, or non-sex chromosomes, the chromosomes 1 till 22. These present equally commonly in those with two X chromosomes (typically assigned female at birth) as in those with an X and a Y chromosome (typically assigned male). X-linked conditions, on the other hand, present more frequently in either of those groups depending on whether they are recessive or dominant.

An example of an X-linked recessive intellectual disability syndrome is Christianson Syndrome. This affects primarily people assigned male at birth because of their XY chromosomes. After all, recessive means that, if a person has an unaffected copy of the X chromosome, that will be dominant and the person (usually assigned female, XX chromosomes) will not have the condition.

At my former care home, there was a man with Christianson Syndrome. He was in his late fifties, which is really old for someone with the syndrome. He, like everyone with the condition, has an intellectual disability. He also has ataxia, although he at least when I still lived there could still walk, unlike most adults with this syndrome. According to the staff, a lot of things made sense now that they knew that he had this syndrome, even his obsession with electronics.

An example of an X-linked dominant intellectual disability syndrome is Rett Syndrome. This only affects people with two X chromosomes (usually assigned female at birth). Fetuses with XY chromosomes and a Rett Syndrome mutation on their X chromosome, will usually be miscarried.

At my old care home, there was another client with Rett Syndrome. I did not know her well though. Rett Syndrome children develop typically until at least six months of age and then regress. They will develop autistic-like behaviors, although social interaction may develop later on. Another typical feature of Rett Syndrome is the loss of hand function. People with Rett Syndrome will usually have involuntary, repetitive hand movements. I do know the client at my old care home loved to play with sensory toys, but I do not know whether she could purposefully manipulate them.

Another syndrome I need to mention is Fragile X Syndrome. This is an X-linked recessive condition, but it does affect some people with XX chromosomes, albeit more mildly. There is also a so-called “premutation”, which is associated with some Fragile X-linked problems later on but not the full syndrome. This “premutation” is differently inherited depending on the sex of the carrier and may lead to a full mutation (Fragile X Syndrome) in their children.

Genetics of Intellectual and Developmental Disabilities #AtoZChallenge

Posted on by Astrid

Hi everyone. I was at my and my husband’s house in Lobith yesterday and, though I fully intended on writing my letter G post while there, I didn’t get to it. Rather than give up on the challenge altogether, I’m going to make up for it today by writing my post now. For my letter G post, my topic is “genetics”. It’s not a topic I know all that much about. I mean, I know the basics of heridity through dominant and recessive, autosomal and X-linked genes. I also know a little about trisomies such as trisomy 21. However, I really don’t think I know much beyond high school biology. For this reason, I am going to provide a very basic introduction to the genetics of intellectual disability based on the info I could find online.

First, of course, not all intellectual disabilities are caused by genetic factors, or solely by genetic factors. Environmental factors such as birthweight and gestational age (ie. whether the child was born prematurely), exposure to substances such as medications or drugs during the fetal period, etc., can contribute to or even cause an intellectual disability too.

That being said, even if the cause of someone’s intellectual disability is (most likely) genetic, it is not always known. There are thought to be approximately 2,500 genes that contribute to intellectual disability, but about half of these haven’t yet been identified. Due to genome and exome sequencing, however, the diagnosis of intellectual disability-related genetic mutations is making advancements.

There are some genetic intellectual disability syndromes that run in families, such as Fragile X Syndrome. However, the majority of individuals with a genetic mutation causing their intellectual disability, did not inherit it from their parents. This means that a future child born to the same family, isn’t at increased risk of being intellectually disabled.

Why, then, would you want to know whether there’s a known genetic cause? Well, a recent article I found on the Dutch Center for Consultation and Expertise website, explains it very well: knowing what syndrome a person has, makes the person’s perspective clearer and may provide ideas for future medical or behavioral intervention. For instance, a doctor cited in the article talked about a girl with a particular genetic mutation causing her intellectual disability which he knew also causes leukemia. The doctor mentioned this to the patient’s primary care physician, who remembered this two years later when the girl complained of significant fatigue. This allowed her to be treated early for what turned out to be leukemia indeed. Another example is the fact that people with Phelan McDermid Syndrome usually experience bipolar-like mood dysregulation in adolescence, which, if not treated, leads to loss of skills. Since these people often have severe intellectual disability, their behaviors could easily be misinterpreted if their syndrome isn’t identified.

Of course, there remains a significant portion of the intellectually disabled population for which no genetic syndrome can be identified. For those with milder intellectual disability and no clear physical features, genetic testing may not even be routinely done. Same for those with other developmental disabilities. In my own case, the possibility of genetic testing was mentioned in my application for one-on-one support, but was immediately dismissed because it’d be “too much for me to handle”. Not that it was ever discussed with me. For all I knew, there was no need for it in my case as my conditions are all attributed to premature birth, with the exception maybe of autism, and people who are just autistic don’t get genetic testing done either.

Weird or Creepy Interests

Posted on by Astrid

Today I have a lot on my mind, but not much I can put down into writing. To occupy you readers anyway, and to distract myself a bit, I’m participating in My Inner MishMash’s Question of the Day. The question is whether you have any interests most people consider weird or even creepy or gross.

Creepy or gross, no. I mean, yes, I’m interested in medicine, but not specifically in anatomy or bodily functions. I have some interest in genetic conditions, particularly rare ones, and of course I’m into psychiatry. Lately, I’ve been connecting the two and learning more about psychiatric aspects of genetic syndromes. I was fascinated when I was told one of my fellow clients has Christianson Syndrome, a form of X-linked intellectual disability that is similar in presentation to Angelman Syndrome. I at first felt weird googling the condition, but since the staff specifically told me about this client’s syndrome rather than me having overheard it, I felt okay in the end.

Weird, yes, definitely. I already commented on the original post that I’m into calendars and timekeeping. I still keep and cherish a twenty-year-old newspaper article explaining why the year 4000 shouldn’t be a leap year, among other things.

I also tend to get upset when people make calendar calculation mistakes, particularly when they do it on purpose. My husband likes to talk about 30th February, for example. As a teen, I used to calculate what day a given date fell on. I was particularly fascinated by dates before 1582, so that I could show people that I knew about the Julian/Gregorian calendar transition.

I also, when I still lived in Apeldoorn, loved riding random buses to memorize their route. Apeldoorn’s buses at least all used to go in an eight-shaped route, each time getting back to the station. That way, I’d never get lost even if I rode a bus I’d never been on before. Before I moved to Nijmegen, I had the bus schedule nearly memorized too.

Currently, I don’t have any weird or unusual interests that I’m particularly actively engaged in. However, when it comes to my “normal” interests, they do tend to be abnormally intense and detail-focused.

Do you have any weird interests?