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Identification of Alu elements mediating a partial PMP22 deletion.
Verena Matejas1, Kathrin Huehne, Christian Thiel
1Institute of Human Genetics, Friedrich Alexander University, Erlangen, Germany.
Neurogenetics
|March 30, 2006
Summary
Hereditary neuropathy with liability to pressure palsies (HNPP) can be caused by smaller, partial deletions of the PMP22 gene. These deletions, mediated by Alu elements, may be missed by standard genetic testing methods.
Area of Science:
- Genetics
- Molecular Biology
- Neurology
Background:
- Hereditary neuropathy with liability to pressure palsies (HNPP) is typically linked to a large deletion in chromosome 17p11.2-12, encompassing the peripheral myelin protein 22 (PMP22) gene.
- Smaller, partial deletions of the PMP22 gene are less common but can also cause HNPP.
Purpose of the Study:
- To identify and characterize a novel, partial deletion of the PMP22 gene in a patient diagnosed with HNPP.
- To investigate the molecular mechanisms underlying this partial deletion and its potential to be missed by conventional diagnostic techniques.
Main Methods:
- Quantitative PCR (qPCR) and Single Nucleotide Polymorphism (SNP) analysis were employed to assess PMP22 gene dosage and allelic status.
- Multiplex Ligation-dependent Probe Amplification (MLPA) was used to define the extent of the deletion.
- Bioinformatic analysis identified Alu elements as potential mediators of recombination.
- PCR and DNA sequencing were utilized to pinpoint the deletion breakpoints and confirm the role of Alu elements in non-allelic homologous recombination (NAHR).
Main Results:
- A partial deletion affecting the 5' region of the PMP22 gene (exons 1-3) was identified in the HNPP patient.
- qPCR and SNP analysis confirmed the deletion of one PMP22 exon 3 allele while retaining two exon 4 alleles.
- MLPA confirmed the deletion spanned the entire 5' region of PMP22.
- PCR and sequencing identified specific Alu elements (AluJo-AluSq and AluYb9-AluSq) involved in the deletion, revealing a shared 29-bp motif with a chi-like sequence.
- These findings suggest that low-copy repeats (LCRs), specifically Alu elements, mediate NAHR in the PMP22 region.
Conclusions:
- Partial PMP22 deletions represent a distinct genetic cause of HNPP that may evade detection by standard STR marker analysis.
- The identified deletion mechanism highlights the role of NAHR mediated by LCRs, such as Alu elements, in generating complex genomic rearrangements.
- Advanced molecular techniques are crucial for accurate diagnosis of HNPP cases involving atypical PMP22 deletions.