R133C and R168X mutations in Japanese Rett syndrome patients: a caution for misdiagnosis

Area of Science:

• Genetics
• Neurodevelopmental Disorders
• Molecular Biology

Background:

• Rett syndrome is a severe neurodevelopmental disorder affecting females, characterized by developmental regression.
• The MECP2 gene is the primary genetic cause identified for Rett syndrome.
• Accurate genetic diagnosis is crucial for understanding disease mechanisms and inheritance patterns.

Purpose of the Study:

• To investigate MECP2 gene mutations in three sporadic Japanese patients diagnosed with Rett syndrome.
• To re-evaluate initial findings of homozygous MECP2 mutations, which contradicted known inheritance patterns.
• To identify potential sources of error in genetic analysis of the MECP2 gene.

Main Methods:

• Analysis of the MECP2 gene in three Rett syndrome patients using direct sequencing.
• Utilized a primer set from a previous MECP2 mutation report, initially suggesting homozygous mutations (R133C, R168X).
• Employed newly designed PCR primers and sequence analysis to confirm heterozygous mutation status and investigate PCR bias.

Main Results:

• Initial sequencing suggested homozygous mutations (R133C and R168X) in the MECP2 gene.
• Further analysis using different PCR primers revealed these mutations were actually heterozygous.
• A nearby C/T polymorphism was identified as the cause of preferential amplification of mutated alleles during PCR.

Conclusions:

• Biased PCR amplification can lead to misinterpretation of MECP2 mutation status, potentially causing misdiagnosis of homozygous mutations.
• This study underscores the importance of careful validation in genetic testing, especially for genes like MECP2.
• Awareness of PCR amplification bias is recommended for accurate mutational analysis in Rett syndrome diagnostics.