Mendelian Disorders

MENDELIAN DISORDERS

Mendelian disorders are characterized by single gene mutations. Common types ofmutations include point mutations and frameshift mutations.

·            Point mutations occur with a single nucleotide base substitution, which mayproduce 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 mis-sense 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 insertion or deletion of bases leads to ashift 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 tran-scription 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.