hemihyperplasia

We have been told by a doctor that my son has hemihypertrophy/hemihyperplasia. do the genetic tests give unambiguous answer if it is really hemihypertrophy? my son is 6 months old and his right leg is slimest then the left one - it's girth is about 2cm smaller, and it is about 0,5 cm shorter. right feet is a bit smaller too. is there any possibility that it is not a hemihypertrophy? could the intrauterine fetal anoxia be the reason of that situation? Maybe you know about any other reason that can bring about such asymmetry?
and one more question: if it is hemihyperplasia - are all tissues bigger/fatter? is it possible that only fatty tissue is bigger? bone and muscular tissues are the same in both legs.

If you could help us with any information we would be extremely grateful.

[Yao Sun, MD, PhD]

As you know, hemihypertrophy or hemihyperplasia is a syndrome in which growth on one side of the body is larger than the other.  Any part of the body can be affected, and different parts of the body can be larger on opposite sides.

It can either be "idiopathic", meaning there is no known cause of the growth difference, or it can be associated with other syndromes such as Beckwith Wiedeman Syndrome.  In both cases, one of the important medical consequences is an increased risk for cancer.  Your son should be followed closely for this risk, and many physicians recommend periodic screening ultrasounds to evaluate for the possibility of various tumors including Wilm's tumor of the kidneys.  There are some genetic tests for Beckwith Wiedeman Syndrome, but no standardized test yet for idiopathic hyperplasia.

Although it is possible that abnormal circulation to a limb from abnormal blood vessels can cause growth discrepancy, this is also a rare cause of hemihyperplasia.  Generalized "fetal anoxia" would not cause hemihyperplasia of isolated body parts.