Chromosome 15q11 related. Results from deletion of paternal copy of imprinted gene (the rare genes where the copy from one parent is turned off by DNA methylation). See also Angelman syndrome (also chromosome 15).

Beware pregnancies with Trisomy 15 where subsequent testing looks like normal diploid…

Classically severe hypotonia at birth, often with mild growth restriction, causing significant feeding difficulties.

Facial appearance characteristic even at birth: high forehead, narrow bifrontal diameter, downturned corners of the mouth, micrognathia, and dysplastic ears. As they age, almond eyes become apparent, face is rather unexpressive of course. Hands are small.

After age 1, ironically, appetite then seems to surge, leading to obesity.

Scottish genomic test directory says test if:

• Severe hypotonia and/or feeding difficulties in early infancy;
• Global developmental delay;
• Hypogonadism;
• Excessive eating with central obesity if uncontrolled in childhood