Table 7.

Methods to Characterize CSTB CCC-CGC-CCC-GCG Repeats

Interpretation of CCC-CGC-CCC-GCG Repeat NumberExpected Results by Method
Conventional PCRExpanded repeat analysis 1
Normal: 2-3Detected 2Expansions can be detected, & repeat size can be approximated 3, 4
Pathogenic (full penetrance): ≥30Not detected
1.

Methods to detect and approximate the size of expanded repeats include long-range PCR sized by gel or capillary electrophoresis and Southern blotting. The upper limit of repeat size detected will vary by assay design, laboratory, sample, and/ or patient due to competition by the normal allele during amplification.

2.

Detection of an apparently homozygous repeat does not rule out the presence of an expanded repeat; thus, testing by expanded repeat analysis is required to detect a repeat expansion.

3.

Southern blotting [Lalioti et al 1997] and a specific PCR protocol [Joensuu et al 2007] for the CCC-CGC-CCC-GCG repeat expansion have been described

4.

Precise sizing of repeats is not necessary as clinical utility for determining the exact repeat number has not been demonstrated.

From: Progressive Myoclonic Epilepsy Type 1

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