People are often surprised when they see a picture of Oscar or meet him for the first time. He's very thin, not what one expects when they hear he has Prader-Willi syndrome and insatiable appetite. In part, he comes by it naturally -- Paul is very tall and thin, and family genetics are a big factor. We also have food security in place to ensure that is healthy and safe, and getting the right amount of calories. But there's more to it than that.
Many years ago, at a National PWS conference we heard that the
ideal weight for a person with PWS is a quartile below their height
percentile. So, if Oscar's height is in the 50th percentile, his weight
should be at about the 25th percentile.
My understanding is that the main reason for this rests in how PWS affects body composition. We've not done the fancy tests, but Oscar has less lean muscle mass and relatively more fat mass than a typical person - and therefore his healthy weight is actually less than that of a typical person of the same height who has more muscle. If he were to gain excessive weight, my impression is that he would gain fat mass at a more rapid pace than lean muscle mass which would put extra strain on his organs. He'd also have extra weight to support but not the increased muscle strength to carry it like typical people do when they gain weight.
Growth hormone therapy helps increase lean muscle mass and reduce fat mass (along with many other positive effects). Oscar has been getting nightly growth hormone shots since he was four months old, and there's no doubt he has benefited greatly. My guess would be that his lean muscle mass is still below average though. And, with less muscle, he looks thinner than expected for his height. I notice this especially in his arms but also his legs.
We work closely
with Oscar's primary care physician and his endocrinologist to make sure
that he is growing and gaining weight at the right pace. And sometimes we need to make adjustments. Just last fall we all agreed that we needed to up his calories to ensure he had enough fuel for puberty. (In case you are wondering, we made these decisions with Oscar out of the room, since discussing increasing calories in front of him would have created major anxiety!)
My two thin (and good-looking) guys.