Body Mass Index in Adults with Prader-Willi Syndrome

Contributed by Susanne Blichfeldt, Georgina Loughnan, Jackie Waters. IPWSO

Body Mass Index, or BMI, is an approximate measure, based on a person’s height and weight, to indicate if they are a health weight. It is calculated by dividing a person’s weight in kilograms by their height in metres squared. You don’t have to get our your calculator though – there are plenty of online calculators which will do it for you, such as the NHS Choices one at https://www.nhs.uk/Livewell/loseweight/Pages/BodyMassIndex.aspx

BMI is divided into a number of ranges

·       below 18.5 – underweight

·       18.5 – 24.9 – healthy weight

·       25 – 29.9 – overweight

·       30 – 39.9 – obese

·       40 or above – severely obese

You may also see BMI depicted as a chart like the one on the right.

How might BMI be different for people with PWS?

Remember, BMI is only an approximate measure. It does not take body composition (fat, muscle, bone) into account. People with PWS generally have a different body composition to most other people, with a greater proportion of fat to muscle mass. For instance, for an active, 150 cm tall person with PWS, weighing 80kg, who does not have difficulty moving around, lean body mass (ie muscle, bones and inner organs) will most often be around 35-40 kg. The rest is fat.

A DEXA scan (dual energy X-ray absorptiometry) is recommended to evaluate the amount of muscle and fat in the body. It can also evaluate the amount of calcium in the bones of adults, and check if the person has osteoporosis, which is quite common among adults with PWS. It is generally recommended that adults with PWS have a DEXA scan every 2-3 years.

It is also very valuable to know the amount of lean body mass, when medication is prescribed, because most medication is primarily distributed in the lean body mass. Too high doses of medication may easily create side effects if the doctor is unaware of the person’s low lean body mass.  A DEXA scan is easy to perform. A GP can refer you to the appropriate hospital service for this.

Those who have lost a lot of weight may also have excess body skin which can lie in skinfolds on their bodies.

Georgina Loughnan, who is an advisor to the International PWS Organisation, and works at the Prader-Willi Syndrome Clinic, a part of Metabolism & Obesity Services, Royal Prince Alfred Hospital, Camperdown, New South Wales, in Australia, says: 

“Regarding having all clients reach a healthy weight Range of BMI – 20-25kg/m2, I have several clients who are in this range now and yes, some, after losing much weight have excess skin on arms and legs. However, with regular effective exercise as a major part of their weight loss programme some have minimal excess skin. I have had several people lose over 50 kg (2 lost 75 kg) and had small abdominal aprons (excess abdominal skin) that just needed to be well washed and dried, but gave them no problems. The key is consistent exercise for the whole body, which is so essential for healthy weight loss.

However, reaching a BMI of 20-25kg/m2 should not be the aim for all people with PWS. A better aim is for a healthy weight that reduces comorbidities and improves physical ability and lifestyle. This is far more important and can be achieved in the overweight BMI category of 25-30kg/m2.”

Dr Susanne Blichfeldt, also an advisor to IPWSO, concurs that exercise is the key. She says, “Just sitting and losing weight means that you lose both muscle and fat tissue, so it is important if you are on a diet to move a lot. Walking is perfect, and swimming and gym are also good to build up muscles.  It is more important to have a weight that does not compromise motor activity, than to try to reach the 20-25 target”.

Does growth hormone treatment make a difference?

According to a Scandinavian study, growth hormone treatments in adults will add about 2 kg more of muscle mass  and 4 kg less of fat on average. However, worldwide there have been no large-scale longitudinal studies of the effects of growth hormone (GH) on muscle mass in adults, and only a very few adults with PWS in the UK receive it, as it is only licensed by NICE (National Institute for Clinical Excellence) up to the age of 18 years in PWS.

BMI and Children

The BMI values mentioned above are to be used for adults only.  BMI charts for children also exist for each age group and, in general, BMI values for normal weight children are lower than for adults, because of a different body composition in children. Normal BMI values are lowest in the youngest age groups.  As all children grow at different rates, you should take the advice of your consultant or dietitian as to whether your child is a healthy weight and developing along the right centile for PWS. 

Thank you

Many thanks to Dr Susanne Blichfeldt, MD, senior consultant and paediatrician, medical advisor to the International PWS Organisation and it Clinical and Scientific Advisory Board,  and to Georgina Loughnan for their contributions to this article and for checking its medical accuracy.

What happens when I get too old?

It's a question I wake up at 3am and wonder about.  And I think this is a question that many of us older parents have started to ask in earnest.  Let’s face it, most of us have been around the PW world for 30, 40 years, maybe even longer depending on our now-adult son or daughter's  age.  When you stop to think,  PWS wasn’t really acknowledged until 1957 when it was described as a condition with a short life-span with major obesity problems, and very little good management procedures.  Knowledge  didn’t really take off until the internet took charge some 30 years later.  Many of us were the generation that forged the PW-pathway, stumbling over rocks and boulders, tripping over roots and blindly turning corners as we went.  So many of our kids didn’t have the benefit of growth hormone treatment and with exercise being that much harder for them with their low muscle-tone, we faced a life of eternal vigilance of food and exercise.  Exercise and food.  And all the challenges that go with that.  It seemed like a lifetime imprisonment with little or no time out for good behaviour!  Schools weren’t really aware of the unique needs of PWS, families had a hard time coming to terms with their ‘different’ sibling, grandparents really didn’t understand, and as for any work placement – well, there was just so much that employers needed to put in place and provide that most of the time it was more often than not just put into the "too hard" basket.  

Our kids are living longer and that ‘short life-span’ that was always talked about 30 years ago has now disappeared.  With the right kind of information, support and management, there’s nothing to stop anyone with PWS from living a long and fulfilled life.  Except that we  parents are growing older, and we are growing tireder.  Although their life-span may be longer, their IQ and competency levels are not any more mature than they were when they were young teenagers.  Sons or daughters still living at home require just as much attention, chivvying, encouraging, as when they were little as that ability to do things for themselves is severely limited.  As parents become tireder and tireder, we ask what are we supposed to do?  We feel guilty if we are not doing the ‘right thing’,  providing enough exercise, enough vigilance.  Many of us can pinpoint illnesses that we experience to the care and worry of providing ongoing support for our sons and daughters: high blood pressure, fatigue, anxiety, heart problems, and more.  It is of real concern that we have a plan in place in the event of our not being able to physically provide care any longer.

Some countries have residential care, but little specialised (ie PW) choice.  Some have good residential providers, and in some countries this simply isn't an option.  Good caregivers can be few and far between.  Not every agency can provide what our 'kids' need and even if we find a good residential care placement, parents still worry and live with anxiety that things will go wrong.  As parents we don’t want to burden other children/adults in the family with the ongoing care responsibilities, nor do we want our adult children (PWS) to go into State care.  

Some of us want to be able to enjoy our last few good years!  We want to knock a few things off that “bucket list”, to travel, or to spend time with other members of the family; we want to go out for a meal, go to the theatre, visit friends, without having to make arrangements for ‘time out’.  

We are asking, what next?  Who will look after my adult child?  How will I provide for them?  How can I provide the management that they need, the exercise and daily walks, outings if I'm not physically able to do this?  And, when I die, how will they manage without me? 

As for me, well after a few 3am consultations with myself I spent some time with a lawyer who explained what I could do to prepare for the eventuality and hopefully in my country it will be enough.  

I really do need to start sleeping again!

I'll tell you what I want, what I really really want!

The other day I listened to my daughter as she picked up the phone, dialled her bank and started to explain what she wanted done for an automatic payment to go to into my account.  She was polite, completely engaged and knew exactly what she wanted.  I have to say that I was impressed. 

She explained that she had special needs and that her benefit covered so much but that she wanted to make sure an extra $5.00 went into her Mum's account so as she could pay back the money she borrowed. She knew exactly what to do and how to do it.

It started me thinking about all the things our kids know how to do and how so many manage, to get by in the world.  There is so much they can do and understand, but the potential for failure and the potential for being misunderstood, not to mention the potential for fallout from unthought-out consequences is high.  Which means that someone in their lives must be one step ahead the whole time. 

My daughter likes to go shopping, wants to have lay-bys, wants to buy presents for everyone,  The consequences don't matter to her because she lives in the here and now.  Warnings about  running into a lot of debt simply pass her by because there's always another payday, The idea of saving money is an anathema to her - what good is putting money aside to spend later when you can spend it today?  Her idea of saving money is to buy from op-shops (and who can argue with that)!

The concept of something unforeseen such as a vet fee for the cat, an unplanned visit to the doctor, a need to go to the dentist, or to make sure there is catfood in the cupboard at the end of the week, is as absurd to her as water-divining.  Much better to rush out and buy the boyfriend a Valentine's Day present in the hope of getting something in return!

She's quite happy that her bank balance comes in as zero each month as it's better to owe money in lay-buys, or 'next month' for the doctor, than to see money resting fretfully in her bank account.

It's difficult to argue with mainly because she will agree with everything I say... then go out and do exactly as she pleases.  And, I have to say that I am fully expecting the $5.00 per week to be uninstated any time now!

There's always another day...