FG; syndrome is an X-linked incomplete recessive condition comprising menta
l retardation, congenital hypotonia, macrocephaly, a distinctive facial app
earance, and constipation or anal malformations. Here, we report on a chrom
osome X inversion [inv(X)(q12q28)] in a boy with FG syndrome and in his men
tally retarded maternal uncle, and we discuss the possible involvement of t
his paracentric inversion in the FG syndrome. (C) 1999 Wiley-Liss, Inc.