Skip to 0 minutes and 7 secondsThere are standardised symbols for drawing pedigrees which have been adopted internationally. Squares for men, circles for women, with coloured in symbols for individuals affected with the condition-- in this case, diabetes. Start with the proband. This is the first individual you come across. And then, add partners. The proband is indicated by a small arrow. Collect information about relatives and their partners in one generation before moving up or down a generation. Then collect information about children, starting with the eldest first, then parents and grandparents until you have as much detail about other family members as possible. Include names, current ages, and ethnic group. Specific information from everyone with diabetes would be helpful, including age at diagnosis, treatment, HbA1c and BMI.
Skip to 1 minute and 3 secondsOther features, for example, glycosuria, oral glucose tolerance test results, C-peptide or antibody results, diabetes complications, renal cysts, uterine abnormalities, miscarriages, causes or ages of death, sulfonylurea sensitivity, deafness, birth weights, neo-natal hypoglycemia, or learning difficulties and epilepsy and neo-natal diabetes can all be extremely helpful in indicating the most likely genetic cause of the diabetes.
Taking a good family history is a key skill which can also aid the recognition of individuals likely to have MODY. Taking a thorough family history can help identify patterns of inheritance and involves asking for information about many family members. It allows pictorial representation of biological relationships between family members in a family tree or pedigree and indicates those family members affected by medical conditions. Ideally a pedigree would include at least 2-3 generations, the minimum would be first degree relatives (children, siblings and parents) of an individual.
Be aware that the information may be very sensitive and include personal issues such as family break ups, miscarriages / stillbirths and bereavements. An accurate family history may help indicate whether genetic testing is appropriate and may reveal family members previously thought to have Type 1 or Type 2 diabetes who may also benefit from genetic testing, confirming one unifying diagnosis. If a family history is not taken, a patient’s relatives are less likely to be considered. Taking a family history can also identify other family members who may be at risk of developing the condition.
In the video you can see an example of how to draw a pedigree or family tree. The example here from a MODY family clearly indicates the three key characteristics of MODY:
- autosomal dominant inheritance
- a young age of onset of diabetes
- non-insulin dependence
However even when a family tree clearly indicates the key features of MODY it is important that healthcare professionals are aware of its significance and are able to make the correct decisions based on this information. Dan has a family history of diabetes inherited in an autosomal dominant fashion across five generations and yet his Mum describes the frustration of highlighting this to health care professionals who did not recognise the importance of these details.
So the fact that Dan has a autosomal dominant family history of diabetes combined with his antibody negative status, the probability score and other family members diagnosed with diabetes below the age of 25 years who were non insulin treated clearly point to an alternative diagnosis to Type 1 diabetes. We offered genetic testing to Dan and this confirmed he had HNF1A MODY.
We will meet Dan again in Week 3 to see what difference having a genetic test made for him and his family.
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