Genetic testing is a very useful tool for health and wellness. Yet all tools have limitations.
“23andMe does not offer diagnostic testing. For testing related to a personal or family history of a particular genetic disease, please consult a healthcare provider in order to ensure that you are pursuing the most appropriate test for your personal situation.”
Topics not included in 23andme reports:
- “Drug response (for example CYP2D6 and certain HLA alleles)
- Copy number variations (CNVs), balanced rearrangements, and mosaicism
- MTHFR analysis, such as a targeted mutation analysis, methylation analysis, or detox profile”
23andme uses genotyping, which is the simple method of identifying single (mostly) character changes in your genetic data. These single character changes are known as variants or Single Nucleotide Polymorphisms (SNPs). But, your genome has several other types of variations that are not detected by this technology.
“23andMe is not designed to analyze for repeated, inserted, inverted, translocated or deleted segments of DNA”
One important type of genomic variation is Copy Number Variations (CNVs). In copy number variations, certain genetic features are repeated again and again as in multiple copies are present. The 23andMe test is not designed to detect these and does not report data on most CNVs.
Hence, the 23andMe health report does not address the following.
- Trisomies (for example trisomy 21 also known as Down syndrome) and copy number variations
- Trinucleotide repeat disorders (for example Fragile X, Huntington’s disease)
- Repeats, insertions, rearrangements, or deletions
Trisomies and copy number variations
There are 23 pairs of chromosomes in most people. The 23rd pair is known as sex chromosome, written as X and Y chromosomes. X carries female features and Y carries male features. In some instances, instead of XX (for females) and XY (for males), an individual may inherit an extra chromosome leading to a condition called Trisomy. Examples of trisomies include Down syndrome (trisomy 21), and Klinefelter syndrome (XXY). These conditions are not detected and reported by 23andMe
Trinucleotide repeat disorders
Certain segments of the genome repeat over and over again. A group of three genomic characters such as CAG can repeat several terms. This type of repeating can lead to diseases such as Huntington's Disease and Fragile X syndrome.
The 23andMe genotyping platform is not capable of detecting trinucleotide repeats and therefore 23andMe reports do not include any condition on trinucleotide repeat disorders. Nor is there relevant data related to trinucleotide repeat disorders in the raw data.
Repeats, insertions, translocations, or deletions
In some cases, genomic features may be deleted or new features inserted (in comparison to reference genomes). Such disorders include DiGeorge syndrome (aka 22q11.2 deletion syndrome) and Cri du Chat syndrome (5p- where part of chromosome 5 is missing).
In addition, the majority of Spinal Muscular Atrophy (SMA) and Duchenne Muscular Dystrophy (DMD) cases are due to loss of genetic material (in each case just part of the gene is missing).
23andme’s technology is not designed to analyze repeated, inserted, inverted, translocated, or deleted segments of DNA, in most cases 23andme cannot provide information about copy number or other genetic features that are related to the number or order of base pairs present.
References
- https://www.23andme.com/dna-health-ancestry/?nav1=true
- https://www.xcode.life/23andme-raw-data/cyp2d6-status-using-dna-raw-data/
- https://www.xcode.life/23andme-raw-data/23andme-mthfr-ancestry-dna-raw-data/
- https://medlineplus.gov/genetics/understanding/genomicresearch/snp/
- https://www.genome.gov/genetics-glossary/Copy-Number-Variation
- https://en.wikipedia.org/wiki/Fragile_X_syndrome
- https://www.cdc.gov/ncbddd/birthdefects/downsyndrome.html
- https://www.mayoclinic.org/diseases-conditions/klinefelter-syndrome/symptoms-causes/syc-20353949
