MED12: is a member of the large Mediator complex, which has a critical and 
central role in RNA polymerase II transcription. As a multiprotien complex, 
Mediator regulates signals involved in cell growth, development, and 
differentiation, and it is involved in a protein network required for 
extraneuronal gene silencing and also functions as a direct suppressor of 
Gli3-dependent Sonic hedgehog signaling. This may explain its role in several 
different X-linked intellectual disability syndromes that share some overlapping 
clinical features. This review will compare and contrast four different clinical 
conditions that have been associated with different mutations in MED12, which is 
located at Xq13. To date, these conditions include Opitz-Kaveggia (FG) syndrome, 
Lujan syndrome, Ohdo syndrome (Maat-Kievit-Brunner type, or OSMKB), and one 
large family with profound X-linked intellectual disability due to a novel 
c.5898insC frameshift mutation that unlike the other three syndromes, resulted 
in affected female carriers and truncation of the MED12 protein. It is likely 
that more MED12 mutations will be detected in sporadic patients and X-linked 
families with intellectual disability and dysmorphic features as exome 
sequencing becomes more commonly utilized, and this overview of MED12-related 
disorders may help to correlate MED12 genotypes with clinical findings.