Stuff that occurs to me

All of my 'how to' posts are tagged here. The most popular posts are about blocking and private accounts on Twitter, also the science communication jobs list. None of the science or medical information I might post to this blog should be taken as medical advice (I'm not medically trained).

Think of this blog as a sort of nursery for my half-baked ideas hence 'stuff that occurs to me'.

Contact: @JoBrodie Email: jo DOT brodie AT gmail DOT com

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Sunday, 6 April 2014

Small post for Sophia about genetic testing for diabetes

For Sophia - I realised this was going to take up more tweets than those following both of us might have patience for.

For everyone else - I was a diabetes science information officer for eight years until June 2012 and as such there may be newer information that I'm not aware of, if you spot any errors in my reasoning below do let me know, ta :)

General 'stuff' about genetic testing for diabetes, saving money for health service

1. What is the benefit to the individual or to the state for sequencing genome with respect to diabetes risk?
I'm not aware of researchers into diabetes genetics having called for widespread genetic testing post-birth (or at any other time), even in people at risk.

I might be wrong but I don't think genetic testing (we're really talking about Type 2 diabetes here) tells you much that you don't already know. Age, family history, weight and activity levels are possibly a better predictor of T2D. Family history obviously implies genetics, but it seems to be a pretty multifactorial sort of thing.

As the information below (which comes from Diabetes in the UK 2012) suggests, most cases of Type 1 diabetes don't seem to have an obvious family link, though there are genes that increase risk of developing the condition.
Type 1 diabetes
Although more than 85% of Type 1 diabetes occurs in individuals with no previous first degree family history, the risk among first degree relatives is about 15 times higher than in the general population.

On average: if a mother has the condition, the risk of developing it is about 2–4 per cent
if a father has the condition, the risk of developing it is about 6–9per cent
if both parents have the condition, the risk of developing it is up to 30 per cent
if a brother or sister develops the condition, the risk of developing it is 10 per cent
(rising to 10–19per cent for a non-identical twin and 30–70 per cent for an identical twin).

Type 2 diabetes
There is a complex interplay of genetic and environmental factors in Type 2 diabetes. It tends to cluster in families. People with diabetes in the family are two to six times more likely to have diabetes than people without diabetes in the family.
There doesn't seem to be very much that someone can do to prevent getting Type 1 diabetes, whereas health interventions can help reduce the risk of Type 2 (and prevent progression from "prediabetes"to full-blown Type 2 diabetes). However the lifestyle advice given to someone at risk of developing T2 is pretty much the same as would be given to anyone: eat a variety of foods, not too much, maintain a healthy weight, do a bit of exercise but doesn't need to be marathon-running to help.

Perhaps giving someone information in black and white from a genetic test might make them more likely to follow this healthy advice (but is this coercion or compliance!) however the tests themselves, even in high-risk individuals, don't appear to be all that sensitive or of use in clinical practice.

Genetic Screening for the Risk of Type 2 Diabetes: Worthless or valuable? Diabetes Care 2013
"Genetic testing for the prediction of type 2 diabetes in high risk individuals is currently of little value in clinical practice.
The limitations of genetic risk models are small effect size of genetic loci, low discriminative ability of the genetic test, small added value of genetic information compared with the clinical risk factors, questionable clinical relevance of some genetic variants in disease prediction, and the lack of appropriate models for studies of gene-gene and gene-environment interactions in the risk prediction. 

For improvement of the genetic risk models in the future, the definition of type 2 diabetes and classification of subtypes of diabetes should be more precise, new sequencing techniques should be applied to identify low-frequency and rare variants having a large effect size, non–European ancestry populations should be investigated to identify new variants relevant to type 2 diabetes prediction, studies of structural variation and epigenetics should be performed to identify new variants relevant to type 2 diabetes prediction, and modern statistical methods should be developed and applied in studies of gene-gene and gene-environment interaction in large populations." - emphasis added.
I don't think there's much benefit in genetic testing either to a person at risk of diabetes, or the state at this stage.

2. What is the benefit to the individual or to the state in diagnosing diabetes early?
With undiagnosed Type 1 diabetes things can go wrong very quickly as with no insulin available and rising glucose levels the person can go into diabetic ketoacidosis (DKA), a metabolic emergency that can and does result in death. So clearly a benefit to the individual there! Once T1D is diagnosed if the person doesn't take sufficient insulin this problem can re-occur.

Diabetes UK had a campaign to get parents more aware of the symptoms of Type 1 diabetes - the 4Ts: toilet, tired, thirsty, thinner (going to the loo more, drinking more water to compensate and losing weight along with being tired as the body's not getting the glucose fuel it needs).

With undiagnosed Type 2 diabetes the person may creak on fairly happily, and fairly unaware that there's a problem. Here insulin is still produced by the pancreas and the main problem is that the body (organs, muscles) become less sensitive to it). Any symptoms are generally put down to 'getting older' and that's why symptoms are pretty useless for Type 2 (good for Type 1), and 'risk factors' are much more important - as in T1 a blood test is diagnostic.

About half of people who are diagnosed with Type 2 diabetes will already have some signs of diabetic complications, so early diagnosis can help to prevent these from worsening (it's controversial but not unfeasible that some complications may be reversible if caught early). Plus people tend to feel a lot better once their glucose levels are brought back to healthier levels (also it's not just glucose, diabetes is a cardiovascular condition and blood pressure and blood fats / lipids are also problematic and need to be monitored).

There are other rarer forms of diabetes and some of these can be linked strongly to a particular gene - monogenic forms of diabetes can be probed with genetic testing however the person is already likely to have been diagnosed with 'diabetes' (probably Type 2*) and this testing really just refines the diagnosis rather than spots the existence of the diabetes. The advantage of a correct diagnosis is that the person gets the right treatment (in some cases this can be changing from insulin to tablets).

From the state / money point of view - diabetes complications cost a lot of money and diabetes medicine costs a lot too. Hospital admissions and cardiovascular treatments are probably the big costs and likely to increase with an aging population. Delaying or preventing complications saves money, though offset by more people taking medication. Insulin's main side-effect arises because it's incredibly difficult to get the dose right - if too much is taken then blood glucose levels can plummet and the person may need medical treatment. If too little is taken then the person may experience the metabolic emergency DKA mentioned above, which requires hospital treatment.

See also 
Article: Health Economics
Estimating the current and future costs of Type 1 and Type 2 diabetes in the UK, including direct health costs and indirect societal and productivity costs Diabetic Medicine 2012

I think a more feasible thing is perhaps to forgo predictive testing at this stage (maybe it'll be more useful in the future) but improve prompt rather than early (pre) diagnosis of any kind of diabetes so that the person can maintain good health for longer. 

*After I tweeted this post and asked for corrections @sparklyredshoes pointed out that people ultimately diagnosed with a monogenic form of diabetes are possibly more likely to have been initially misdiagnosed with Type 1 (not Type 2 as I've said above) as they're often 'young and skinny'. However there aren't really enough stats on this so she suggested that it was probably safer for me not to commit to which type of diabetes people are commonly misdiagnosed with :)

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