The molecular lesion responsible for the phenotype is a point mutation resulting in a T-to-A transversion at nucleotide 80 (ENSMUST00000025992.6, 265-amino-acid isoform), leading to an amino acid exchange from isoleucine to asparagine at position 27, thereby affecting the functional BTB domain of the protein. The mutation presumably causes a loss of function via a dominant-negative mechanism. (J:250423)