Point Mutation Analysis: Genetic Disorders

A point mutation is defined as a change affecting a single nucleotide base in the DNA sequence. Common types include substitutions, insertions, or deletions of one base.

Mutation Types in Listed Disorders

• Haemochromatosis: Typically results from missense mutations like C282Y in the HFE gene, which are single nucleotide substitutions, hence classified as point mutations.
• Hereditary motor and sensory neuropathy type 1 (HMSN1): This condition, often associated with Charcot-Marie-Tooth disease type 1A, is frequently caused by large-scale genomic rearrangements such as duplications or deletions in the PMP22 gene. These larger changes distinguish it from point mutations.
• Achondroplasia: It is predominantly caused by a specific G-to-A substitution mutation in the FGFR3 gene, which is a classic example of a point mutation.
• $\alpha$-1 antitrypsin deficiency: The common Z variant arises from a GAG-to-AAG substitution (Glu342Lys) in the SERPINA1 gene, a type of point mutation.

Identifying the Non-Point Mutation Example

Comparing the genetic basis of these disorders, Hereditary motor and sensory neuropathy type 1 stands out as it is commonly caused by duplications or deletions, not single base alterations. Therefore, it is not an example of a point mutation.