Cell Differentiation/physiology; Hedgehog Proteins/metabolism; Hirschsprung Disease/genetics; Hirschsprung Disease/physiopathology; Neuroglia/physiology; Receptors, Notch/metabolism; Animals; Cells, Cultured; Enteric Nervous System/cytology; Enteric Nervous System/physiology; Epistasis, Genetic; Gastrointestinal Tract/cytology; Gastrointestinal Tract/physiology; Gene Expression Regulation, Developmental; Genetic Predisposition to Disease; Genome-Wide Association Study; Hedgehog Proteins/genetics; Humans; Intracellular Signaling Peptides and Proteins/genetics; Intracellular Signaling Peptides and Proteins/metabolism; Membrane Proteins/genetics; Membrane Proteins/metabolism; Mice; Neural Crest/cytology; Neural Crest/physiology; Neurogenesis/physiology; Neuroglia/cytology; Patched Receptors; Patched-1 Receptor; Polymorphism, Single Nucleotide; Receptors, Cell Surface/genetics; Receptors, Cell Surface/metabolism; Receptors, Notch/genetics; Signal Transduction/physiology