Researcher calls for more genetic testing in diabetes

A leading diabetes researcher is calling for more genetic testing for a rare form of diabetes, monogenic diabetes, after leading research on use of precision medicine in diabetes.

Monogenic diabetes is a group of rare diabetes subtypes caused by changes in a single gene. It is important to diagnose monogenic diabetes because some people may be able to switch from insulin injections to tablets.

Professor Rinki Murphy, of Waipapa Taumata Rau, University of Auckland, led the paper looking at how to apply precision medicine to diagnose people with monogenic diabetes, just published in Nature Communications.

“Currently, the best use for diabetes precision medicine is in monogenic diabetes where a genetic test can directly inform which specific treatment will work best for a patient and point to members of their whānau who may need testing,” Dr Murphy says.

“In Aotearoa, there is a gap in evidence for how best to identify people of Māori and Pacific ancestries who might have monogenic diabetes, in whom diabetes genetic research is lacking so interpreting the genetic tests is more challenging and both the number of referrals and pick up rate is lower than in people of European ancestries.”

One of the several New Zealand patients who have benefited from genetic testing is Penny Rich.

“Many GPs don't know about monogenic diabetes - I feel lucky mine did," Ms Rich says.

"I was gene tested in 2012, aged 56, which showed the exact diabetic gene mutation I had. That simple test has been life-changing for me,” she says.

"For over a decade, I have been given the best medications for my genetic subtype, and have managed excellent diabetic control and (so far!) have none of the usual diabetes-induced health complications,” Ms Rich says.

"As there's a 50 percent chance of inheriting the gene, my wider family have also benefited hugely from diabetic testing. I truly believe that correctly diagnosing diabetes saves lives and improves the health and wellbeing of those who have the illness."

Not every patient is so lucky, Dr Murphy says. For those with neonatal diabetes, an incorrect diagnosis can contribute to lifelong consequences, including neurodevelopmental delay and seizures.

“A genetic test is required for every person who is diagnosed with diabetes within the first year of life because 50 percent will have a genetic form,” Professor Murphy says.

In New Zealand, around 280,000 people have diagnosed diabetes, of whom one percent, or 2,800, would be expected to have monogenic diabetes. Instead, only 300 people have the diagnosis, and annually only around 100 people are tested. The cost of genetic testing is approximately $600-$1200, but a lot less costly to test family members of those known to have a specific type of monogenic diabetes.

For many people, a correct diagnosis of monogenic diabetes means they can come off insulin pumps and take tablets, which will also be more effective and reduce the risk of diabetes complications.

Another patient who was diagnosed with monogenic diabetes when a diabetologist was curious at her being young and slim when diagnosed with type two diabetes, which usually relates to being overweight and older.

Nonetheless, Jodi Rangitaawa was continued on insulin for 25 years, until her mother visited a locum GP. That doctor expressed interest in her mother's diabetes and looked for the 2004 gene testing results. Now her mother is on oral medication and takes only six units of Lantus.

Having the correct diagnosis led to changes in Jodi Rangitaawa’s treatment as well.

She transitioned from insulin to oral medication about a year ago.

“I have lost about 12 kilograms in weight and not because I have changed my diet or started exercising. My last HbA1c was 47. The lowest it’s been for as far as I can remember,” Mrs Rangitaawa says.  

Mrs Rangitaawa’s whānau have benefited from genetic testing, with half of relatives expected to have the same genetic form of diabetes.

There is clear evidence that the most productive place to increase genetic testing would be whānau of those who have already been diagnosed with monogenic diabetes, and to test everyone who was diagnosed with diabetes in the first year of life.

In addition, genetic testing would be appropriate for people with atypical clinical features for common type 1 or type 2 diabetes, such as those who still have residual insulin production despite being diagnosed with type 1 diabetes or active slim people who have been diagnosed with type two diabetes or gestational diabetes.

Dr Murphy was one of 200 contributors to an international consensus paper on precision medicine in diabetes, published on 5 October in Nature Medicine.

Together with her paper on monogenic diabetes, is expected to inform diabetes clinical practice guidelines in New Zealand and overseas.

One important area for further international research is gathering genomic and other data on non-European populations with diabetes. In New Zealand, diabetes research involving Māori and Pacific genetics and improving diabetes classification and treatment according to individual biomarkers would improve care for these populations.

Read the papers in:

• Nature Medicine
• Nature Communications