FG syndrome (FGS), also known as Opitz-Kaveggia syndrome, is a rare X-linked multiple congenital anomaly/mental retardation (MCA/MR) disorder characterized by high clinical variability and genetic heterogeneity. The cardinal features of the syndrome are congenital hypotonia, delayed development of speech, relative macrocephaly (as compared to height and weight), anal anomalies or severe constipation, and dysmorphic facial features. Five loci have so far been linked to this phenotype on the X chromosome. A recurrent missense mutation in the MED12 gene has been identified as the cause for the subset of FGS cases. Filamin A gene (FLNA) and CASK gene mutations could be another causes of FG syndrome.
