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Table 1. Summary of Molecular Genetic Testing Used in TAR Syndrome

Gene 1Test MethodProportion of Probands with a Pathogenic Variant Detectable by This Method
RBM8ADeletion/duplication analysis 2~95% 3
Sequence analysis 4~3% 5
Targeted mutation analysis 6, 7100% for the targeted mutation(s)

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

2. Testing that identifies exonic or whole-gene deletions/duplications 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) that includes this gene/chromosome segment.

3. Detects a 200-kb minimally deleted region at 1q21.1 that includes RBM8A. Because the deletion often extends beyond the 200-kb minimally deleted region [Klopocki et al 2007], a test that can approximate the extent of the deletion is optimal.

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. Heterozygous RBM8A hypomorphic mutations identified in 51/53 affected individuals with the 200-kb deletion and biallelic RBM8A pathogenic variants in 2/53 affected individuals who do not have the 200 kb deletion [Albers et al 2012]. Sequencing analysis requires inclusion of 5’ UTR and intronic gene regions.

6. The two known hypomorphic mutant alleles are c.-21G>A and c.67+32G>C (see Molecular Genetics and Table 2).

7. Pathogenic variants included in a panel may vary by laboratory.

From: Thrombocytopenia Absent Radius Syndrome

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