title: Phenotypic heterogeneity
text: # Phenotypic heterogeneity
  
  Phenotypic heterogeneity describes different mutations in the same gene that can sometimes give rise to strikingly different phenotypes.
  
  E.g., certain loss-of-function mutations in the RET gene, which encodes a receptor tyrosine kinase, can cause dominantly inherited failure of development of colonic ganglia, leading to defective colonic motility and severe chronic constipation (Hirschsprung disease).
  
  