Mendelian disorders are characterized by single-gene mutations.
Mendelian disorders are characterized by single-gene mutations. Common types of mutations include point mutations and frameshift mutations.
- Point mutations occur with a single nucleotide base substitution, which may produce a variety of effects. The form of point mutation called synonymous mutation (silent mutation) occurs when a base substitution results in a codon that codes for the same amino acid. The form of point mutation called missense mutation occurs when a base substitution results in a new codon and a change in amino acids. The form of point mutation called a nonsense mutation occurs when a base substitution produces a stop codon and therefore produces a truncated protein.
- Frameshift mutations occur when the insertion or deletion of bases leads to a shift in the reading frame of the gene.
The location of a mutation will alter its potential effects. Mutations involving coding regions of DNA may result in abnormal amino acid sequences; decreased production of the protein; truncated or abnormally folded protein, or altered or lost function of the protein. Mutations of promoter or enhancer regions may interfere with transcription factors, resulting in decreased transcription of the gene.
Patterns of inheritance for genetic diseases show wide variation, and the genetic pattern of a disease may be classified as autosomal dominant; autosomal recessive; X-linked recessive; X-linked dominant; triplet repeat mutations; genomic imprint-ing; mitochondrial; or multifactorial.