Prenatal diagnosis in Coffin‐Lowry syndrome demonstrates germinal mosaicism confirmed by mutation analysis

Coffin‐Lowry syndrome is a rare X‐linked, semi‐dominant mental retardation syndrome resulting from mutations of the ribosomal S6 kinase 2 (RSK2) gene. In the present report, a male patient affected with Coffin‐Lowry syndrome is shown to have a nonsense mutation of the RSK2 gene. His unaffected mother does not have this mutation in her lymphocytes. In her third pregnancy prenatal diagnosis by mutation analysis has detected gonadal mosaicism. As this is the second report of germinal mosaicism in Coffin‐Lowry syndrome, the finding has important implication for genetic counselling. Copyright © 2001 John Wiley & Sons, Ltd.