Table 1. Summary of Molecular Genetic Testing Used in Mitochondrial Nonsyndromic Hearing Loss and Deafness

Gene 1 Proportion of Nonsyndromic Hearing Loss and Deafness Attributed to Mutation of this Mitochondrial GeneTest Method
MT-RNR1~71%Targeted mutation analysis 2, 3
Sequence analysis 4, 5
MT-TS1 ~29%Targeted mutation analysis 6, 7
Sequence analysis 4, 5

1. See Table A. Genes and Databases for chromosome locus and protein name. See Molecular Genetics for information on allelic variants.

2. Pathogenic variants included in a panel vary by laboratory. All laboratories include m.1555A>G, some include m.961_962delTinsC(n), and some include additional pathogenic variants [Casano et al 1999]. For m.961_962delTinsC(n), the (n) indicates that a variable number of C nucleotides can be inserted.

3. The percentage of individuals with mitochondrial nonsyndromic hearing loss and deafness caused by the m.1555A>G allele varies by ethnicity: approximately 17% in a cohort of European origin and in a Spanish cohort; 5% to 13% in persons of Chinese and east Asian background

4. 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.

5. Sequence analysis can detect the specific pathogenic variants included in targeted mutation panels in addition to other sequence variants.

6. Pathogenic variants included in a panel vary by laboratory. All laboratories include m.7445A>G, some also include m.7443A>G, m.7444G>A, m.7445A>C, m.7510T>C, m.7511T>C [Sevior et al 1998, Pandya et al 1999, Hutchin et al 2000, del Castillo et al 2002], and some include other pathogenic variants.

7. Fewer than 2.5% of individuals with mitochondrial nonsyndromic hearing loss and deafness caused by mutation of MT-TS1 have one of the following alleles: m.7443A>G, m.7444G>A, m.7445A>C.

From: Nonsyndromic Hearing Loss and Deafness, Mitochondrial

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