Molecular Genetic Diagnostic Techniques in Choroideremia

Purpose: To optimize and streamline molecular genetics techniques in diagnosing choroideremia (CHM).

Methods: PCR primers were designed for exons 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 15 of the CHM gene. Each PCR protocol was optimized so that all exons could be amplified with the same component ratio and PCR conditions. Sense and antisense primers were tested for their ability to be used as sequencing primers. Fibroblast cells were cultured, and an immunoblot analysis was performed to detect the presence or absence of Rab escort protein 1 (REP-1) in a suspected CHM patient sample when no mutation was detected with sequencing. Multiplex ligation-dependent probe amplification (MLPA) of the CHM gene was performed and used to detect deletions and duplications in affected males and female carriers. RNA analysis using cDNA was used to detect the presence or absence of the CHM transcript and to search for splice defects.

Results: The newly designed PCR primers allow for more efficient PCR preparation and sequencing to detect point mutations in affected males and female carriers. Immunoblot successfully detects the absence of REP-1 in a CHM patient. MLPA identifies deletions and duplications spanning multiple exons in the CHM gene. RNA analysis aids in detecting splice variants.

Conclusions: The development of new molecular biology techniques and ongoing optimization of existing methods allows for an improved integrated approach to confirm CHM diagnosis and carrier status in consideration of patient family history and available patient sample materials. CHM can be confirmed with an immunoblot assay. To detect the molecular cause of CHM, an examination of the genomic DNA or the mRNA must be performed. Presymptomatic carriers with no identifiable fundus signs can be identified only through molecular analysis of genomic DNA or through quantitative assays.