DNA Traits · Reproductive biology
Fraternal twinning, SMAD3 marker
The chance of conceiving non-identical twins without fertility treatment.
What the research found
In the cited research, the C allele at rs17293443 was associated with a higher likelihood of a spontaneous fraternal-twin birth in women studied.
- TT
- Less likely
- CT
- Middle
- CC
- More likely
What the study found
In the study, each copy went with chance of a twin birth, in relative terms about 9% higher on average.
- Evidence
- Genome-wide association with independent replication
- Who was studied
- Mothers of spontaneous fraternal twins and controls of European ancestry (Netherlands, Australia, USA), replicated in Iceland
The research behind this card was done only in women, so it is part of a report requested as female.
How common each genotype is
| Region | TTLess likely | CTMiddle | CCMore likely |
|---|---|---|---|
| All regions2,504 people | 81% | 17% | 2% |
| Africa661 people | 95% | 5% | Not seen |
| The Americas347 people | 76% | 22% | 3% |
| East Asia504 people | 88% | 10% | 2% |
| Europe503 people | 59% | 37% | 5% |
| South Asia489 people | 80% | 19% | 1% |
Among the 2,504 people of the 1000 Genomes Project, in five world regions. These percentages describe groups of people, never anyone’s chance of having a trait.
Through time
How often the studied letter was read in ancient people, era by era, in the region chosen.
| Before farmingbefore 6500 BC | 11%5 of 46 copies read |
|---|---|
| First farmers6500 to 3000 BC | 25%191 of 760 copies read |
| Bronze Age3000 to 1200 BC | 22%145 of 646 copies read |
| Iron Age and Antiquity1200 BC to AD 600 | 24%207 of 855 copies read |
| Middle AgesAD 600 to 1500 | 24%130 of 543 copies read |
| Today1000 Genomes | 23%231 of 1,006 copies |
Neanderthal and Denisovan genomes
- Altai Neanderthal
- No copies
- Vindija Neanderthal
- No copies
- Chagyrskaya Neanderthal
- No copies
- Denisovan
- No copies
Neanderthals and Denisovans carried the other letter, so this letter is younger than our split with them.
The marker
- Gene or region
- SMAD3
- Marker
- rs17293443
- Location
- Chromosome 15 · GRCh37 67,437,863 · GRCh38 67,145,525
- Letters studied
- C and T, with C as the studied allele
A DNA Traits report reads this marker in your raw DNA file and shows which of the three genotypes is yours, with how common it is. It counts the copies of the studied allele; it does not measure the trait itself.
- Marker
- SMAD3 · rs17293443
- Location
- Chromosome 15 · GRCh37 67,437,863 · GRCh38 67,145,525
- Studied allele
- C
- Published statistic
- Discovery OR 1.27 per C allele (95% CI 1.19 to 1.35), P 1.57e-8, 1,980 mothers of spontaneous DZ twins and 12,953 controls, C frequency 0.24; Iceland replication OR 1.15 (95% CI 1.07 to 1.23), P 1.44e-4, 3,597 mothers of twins and 297,348 controls, C frequency 0.21; combined P 6.29e-11 (Table 3). Twin-birth risk +9% per maternal C allele over about 90,000 Icelandic births (Results). Mbarek 2024 meta-analysis (8,265 mothers of DZ twins, 264,567 controls): beta -0.098 (SE 0.013) per T allele, P 1.39e-13, T frequency 0.772 (Table 2) (Abstract; Results paragraph on the relative risk of twin birth)
- 1000 Genomes Project phase 3, people with 0, 1 and 2 copies
- All regions 2024 / 433 / 47 · Africa 631 / 30 / 0 · The Americas 262 / 75 / 10 · East Asia 446 / 50 / 8 · Europe 295 / 185 / 23 · South Asia 390 / 93 / 6
What it cannot tell you
This maternal association concerns spontaneous fraternal twins, not identical twins or twins conceived after fertility treatment. The 9% is a relative change on a small starting chance.
Identification of Common Genetic Variants Influencing Spontaneous Dizygotic Twinning and Female Fertility (Mbarek et al., 2016)More in Reproductive biology
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See your own two letters.
Upload the raw DNA file you already have. Your report reads this marker and every other card studied for you, each with its evidence and its limits.