MECP2 and microcephaly: Mecp2-knockout (Mecp2-KO) mice, lacking either exon 3 or both exons 3 and 4 (Chen et al., 2001; Guy et al., 2001) or carrying a truncated allele of Mecp2 at amino acid 308 (Shahbazian et al., 2002) undergo a period of normal development, followed by severe progressive neurological phenotypes such as motor impairments, seizures, stereotypic forepaw movements, hypoactivity, and microcephaly.