Low level of mosaicism in atypical Prader Willi syndrome: detection using fluorescent in situ hybridization

Prader Willi syndrome (PWS) most commonly is due to paternal micro-deletion of 15q11-q13. Although PWS is not a rare condition, mosaic micro-deletion cases are reported rarely. FISH using PWS micro-deletion probe is the most useful method to detect deletion including mosaicism. In this report we describe a female child with clinical features of atypical PWS and FISH analysis showing mosaicism for deletion in the PWS critical region. This is first mosaic deletion case of PWS from Indian subcontinent.