Differential recognition and degradation of mutated transcripts can occur due to the location of the PTC either 5’ to the NMD boundary (NMD-competent) or 3’ to the NMD boundary (NMD-incompetent). (A) If the mutation is located within an NMD-competent region of the transcript, NMD will degrade the transcript, depleting the truncated peptide product from the cell, and preventing its toxic effects. This means that a heterozygous carrier of the mutated gene can still rely on the wild type allele for proper function, leading to an autosomal recessive pattern of inheritance. (B) If the mutation is located within an NMD-incompetent region of the transcript, it is not recognized by NMD, allowing the truncated peptide product to accumulate, causing catastrophic damage to the cell, which leads to an autosomal dominant pattern of inheritance.