In this study, the authors investigated abnormalities in myelin (1) tissue (an electrically-insulating layer which forms a sheath around nerve fibers) in MRI (2) brain scans of 9 AS patients.

In MRI scans of seven AS patients before the age of 25 months, showed in all but one of them delayed myelination. Myelination begins in the fetus early in the 3rd trimester with the most rapid period of myelination occurring in the first two years of life. The myelination process follows a specific time course and pattern. This allows one to analyze whether the observed myelination pattern corresponds with the age of the patient.

The scans of three patients taken after the age of 29 months (2.5 years, 3 years, 5 years) all showed complete myelination. However, still subtle myelination deficits were observed in the corpus callosum, the major fiber bundle connecting the two hemispheres.

Taken together these finding suggest delayed myelination in young AS patients, and subtle myelination effects in older AS

Implications:
This is the largest study focusing on myelination in AS. What do these findings implicate in terms of mechanism of disease or possibilities for treatment? This is hard to tell, since we do not know what the effect of such a developmental delay of myelination is on brain function. Similarly we do not know the effect of the subtle myelination deficits which were observed in the corpus callosum.

Nevertheless these findings are valuable for two reasons:
First, there have been many studies published reporting abnormalities in the functioning of neurons in AS. Since an intact myelin sheath is essential for the propagation of electrical signals in neurons, the described changes may well contribute to the delayed development.
Second, it will be of diagnostic importance. Infants with AS sometimes present with a rather unspecific phenotype of developmental delay before the age of one to two years. Brain imaging is often performed in these kids to search for underlying brain abnormalities. Before, delayed myelination patterns were often seen as evidence against the diagnosis of AS, but now we have learned that infants with AS can present with these abnormalities. As a consequence these findings in an infant should guide doctors to consider AS. The diagnosis of AS should still be made based upon clinical and EEG findings and supported by genetic testing.

Glossary:
(1) Myelin: an electrically-insulating layer which forms a sheath around nerve fibers

(2) MRI: magnetic resonance imaging. MRI technology has a high sensitivity for changes in myelination.

Topic: Clinical research/brain imaging in AS
Title: Abnormal myelination in Angelman syndrome
Authors: Inga Harting, Angelika Seitz, Dietz Rating, Klaus Sartor, Johannes Zschocke, Bart Janssen, Friedrich Ebinger and Nicole I. Wolf
Journal: Eur J Paediatr Neurol. 2008 Jun 21
(Contributed by Susan Goorden & Ype Elgersma, Erasmus MC, Rotterdam, The Netherlands).