Mouse Genome Informatics
involves: 129/Sv * C57BL/6
phenotype observed in females
phenotype observed in males
N normal phenotype
• 36% of homozygotes die between 3 and 6 weeks of age

• homozygotes often display growth retardation after weaning
• homozygotes often display distended abdomens after weaning

digestive/alimentary system
• upon autopsy, symptomatic homozygotes display distended ceca packed with chyme
• on a hybrid 129/Sv x C57BL/6 background, 43% of homozygotes develop symptomatic megacolon after 3 weeks of age, with no significant differences in the time of onset and frequency between males and females; the remaining 57% are asymptomatic
• upon autopsy, the proximal colon is always massively distended and packed with chyme, whereas the distal colon appears constricted
• only occasional homozygotes develop symptoms of megacolon after 7 weeks of age
• progeny of asymptomatic homozygotes display a reduced incidence of megacolon (18%)
• Background Sensitivity: susceptibility to megacolon appears to be reduced following initial backrossing onto the 129/Sv background
• upon autopsy, many homozygotes display a distended distal ileum

nervous system
• at P14, homozygotes are viable and overtly normal with no detectable abnormalities in sympathoadrenal cells or in cranial, dorsal root, sympathetic or parasympathetic ganglia
• symptomatic homozygotes display a 47% increase in the number of myenteric ganglia per field in the proximal colon along with a 86% increase in the distal colon
• similar changes in the number of myenteric ganglia are observed in the proximal and distal colon of asymptomatic homozygotes, indicating that myenteric ganglia hyperplasia occurs before megacolon development
• myenteric ganglia from proximal and distal colon are significantly hypertrophic in both symptomatic and asymptomatic homozygotes relative to wild-type controls
• in contrast, the number and size of ganglia in the distal ileum is normal
• no changes in the average thickness of colonic circular and longitudinal muscle are observed, indicating normal smooth muscle growth
• symptomatic homozygotes exhibit a 60% increase in the number of myenetric neurons/ganglion in the proximal colon along with a 66% increase in the number of neurons/ganglion in the distal colon; similar changes are observed in asymptomatic homozygotes
• in addition, homozygotes show a 41% increase in NADPH diaphorase-stained inhibitory myenteric neurons/ganglion in proximal colon along with a 130% increase in distal colon
• in contrast, homozygotes display a 22% decrease in the number of neurons/ganglion in the distal ileum (with no apparent changes in proximal ileum), and a 58% decrease in NADPH-stained inhibitory neurons/ganglion in the distal ileum

Mouse Models of Human Disease
Neuronal Intestinal Dysplasia, Type B 601223 J:40722
Visceral Neuropathy, Familial, Autosomal Recessive 243180 J:40722