ZFHX1B encodes Smad-interacting protein 1, a transcriptional corepressor 
involved in the transforming growth factors beta (TGFbeta) signaling pathway. 
ZFHX1B mutations cause a complex developmental phenotype characterized by severe 
mental retardation (MR) and multiple congenital defects. We compared the 
distribution of ZFHX1B transcripts during mouse and human embryogenesis as well 
as in adult mice and humans. This showed that this gene is strongly transcribed 
at an early stage in the developing peripheral and central nervous systems of 
both mice and humans, in all neuronal regions of the brains of 25-week human 
fetuses and adult mice, and at varying levels in numerous nonneural tissues. 
Northern blot analysis suggested that ZFHX1B undergoes tissue-specific 
alternative splicing in both species. These results strongly suggest that ZFHX1B 
determines the transcriptional levels of target genes in various tissues through 
the combinatorial interactions of its isoforms with different Smad proteins. 
Thus, as well as causing neural defects, ZFHX1B mutations may also cause other 
malformations.