Is the RET proto-oncogene involved in the pathogenesis of intestinal neuronal dysplasia type B?

Hirschsprung disease (HSCR) is defined by the absence of intramural ganglia of Meissner and Auerbach along variable lengths of the gastrointestinal tract. Intestinal neuronal dysplasia (IND) type B is characterized by the malformation of the parasympathetic submucous plexus of the gut. A connection appears to exist between these two enteric nervous system abnormalities. Due to the major role played by the RET proto-oncogene in HSCR, we sought to determine whether this gene was also related to INDB. dHPLC techniques were employed to screen the RET coding region in 23 patients presenting with INDB and 30 patients with a combined HSCR+INDB phenotype. In addition, eight RET single nucleotide polymorphisms (SNPs) were strategically selected and genotyped by TaqMan technology. The distribution of SNPs and haplotypes was compared among the different groups of patients (INDB, HSCR+INDB, HSCR) and the controls. We found several RET mutations in our patients and some differences in the distribution of the RET SNPs among the groups of study. Our results suggest an involvement of RET in the pathogenesis of intestinal INDB, although by different molecular mechanisms than those leading to HSCR. Further investigation is warranted to elucidate these precise mechanisms and to clarify the genetic nature of INDB.

Neural crest cell survival is dependent on Rho kinase and is required for development of the mid face in mouse embryos.

Neural crest cells (NCC) give rise to much of the tissue that forms the vertebrate head and face, including cartilage and bone, cranial ganglia and teeth. In this study we show that conditional expression of a dominant-negative (DN) form of Rho kinase (Rock) in mouse NCC results in severe hypoplasia of the frontonasal processes and first pharyngeal arch, ultimately resulting in reduction of the maxilla and nasal bones and severe craniofacial clefting affecting the nose, palate and lip. These defects resemble frontonasal dysplasia in humans. Disruption of the actin cytoskeleton, which leads to abnormalities in cell-matrix attachment, is seen in the RockDN;Wnt1-cre mutant embryos. This leads to elevated cell death, resulting in NCC deficiency and hypoplastic NCC-derived craniofacial structures. Rock is thus essential for survival of NCC that form the craniofacial region. We propose that reduced NCC numbers in the frontonasal processes and first pharyngeal arch, resulting from exacerbated cell death, may be the common mechanism underlying frontonasal dysplasia.