Table 1.

Summary of Molecular Genetic Testing Used in Giant Axonal Neuropathy

Gene 1Test MethodProportion of Probands with a Pathogenic Variant Detectable by this Method
GANSequence analysis 270%-90% 3
Deletion/duplication analysis 4Unknown 5
1.

See Table A. Genes and Databases for chromosome locus and protein name. See Molecular Genetics for information on allelic variants detected in this gene.

2.

Sequence analysis detects variants that are benign, likely benign, of unknown significance, likely pathogenic, or pathogenic. Pathogenic variants may include small intragenic deletions/insertions and missense, nonsense, and splice site variants; typically, exonic or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.

3.

Using sequence analysis, Bomont et al [2000] identified pathogenic variants in all 22 families analyzed. Except for two heterozygous pathogenic variants in two families, all pathogenic variants (95% of total pathogenic variants) were identified within the 11 exons of GAN. This indicates that the failure to find a pathogenic variant most likely resulted from limitations of the testing methodology rather than genetic locus heterogeneity. Pathogenic variants in these families may be located in regions of the gene that were not sequenced (e.g., introns) or may be of a mutation type not detectable by sequence analysis (e.g., larger deletions, duplications).

4.

Testing that identifies exonic or whole-gene deletions/duplications are not detectable by sequence analysis of the coding and flanking intronic regions of genomic DNA. Included in the variety of methods that may be used are: quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and chromosomal microarray (CMA) (also known as CGH array) that includes this gene/chromosome segment.

5.

Among the 60 total distinct pathogenic variants identified to date, four large deletions have been reported. Deletions can encompass almost the entire gene [Buysse et al 2010] or only a few exons [Boizot et al 2014].

From: Giant Axonal Neuropathy

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