What you carry at this position in your DNA and what research says about it.
Breast Cancer Risk: 10/10 evidence, 21 publications.
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Sample genotype (not yours): C/C
Typical Breast Cancer Risk
Baseline risk for breast cancer and typical blood pressure levels characterize this genetic profile. Lacking the risk-associated T allele helps maintain normal regulatory control of protective genes.
What this genotype means: Typical breast cancer risk; Typical blood pressure levels; Typical risk of Parkinson's disease.
Sample genotype (not yours): C/T
Moderately Increased Breast Cancer Risk
One copy of the T allele is associated with a moderately increased risk of breast cancer and slightly higher blood pressure. This genetic change slightly reduces the expression of a protective tumor suppressor gene.
What this genotype means: Moderately increased breast cancer risk; Slightly elevated systolic blood pressure; Slightly increased risk of Parkinson's disease.
Sample genotype (not yours): T/T
Increased Breast Cancer Risk
Two copies of the T allele are associated with the highest risk of breast cancer at this locus and slightly elevated blood pressure. This genetic profile significantly reduces the expression of a protective tumor suppressor gene.
What this genotype means: Increased breast cancer risk; Slightly elevated systolic blood pressure; Increased risk of Parkinson's disease.
Gene function and biological role
Gene Function: The CASC16 (cancer susceptibility candidate 16) gene, also known as LOC643714, encodes a long non-coding RNA that plays a significant role in regulating gene expression [1]. It is located on chromosome 16q12.1, a region heavily implicated in breast cancer susceptibility [2]. CASC16 is expressed at higher levels in breast cancer cells compared to normal breast tissue [1]. It functions primarily by modulating the binding affinity of the transcription factor FOXA1 to chromatin, which in turn regulates the expression of the nearby tumor suppressor gene TOX3 [3]. Alterations in this regulatory pathway can disrupt normal cell cycle control and apoptosis, contributing to tumor development [3].
Variant Impact: Located within an intron of the CASC16 gene, rs4784227 is a single nucleotide polymorphism that influences gene regulation. This genetic change alters the DNA sequence at a binding site recognized by the transcription factor FOXA1 [3]. Specifically, the T allele increases the binding affinity of FOXA1 to this region compared to the C allele [3]. This enhanced binding recruits transcriptional repressors, which subsequently reduces the expression of the neighboring TOX3 gene [3]. Because TOX3 acts as a critical regulator of chromatin structure and cell survival, its downregulation is linked to increased susceptibility to breast cancer [1].
Key Insight: This variant does not alter a protein directly; instead, it changes how tightly a regulatory protein binds to DNA, which downstream reduces the expression of a protective tumor suppressor gene.
Location: CASC16. Chromosome 16 · 16q12.1 · 52.6 Mb
Estimated prevalence by population
Global 64.7%; European 57.5%; African 87.4%; East Asian 56.8%; South Asian 62.6%; Americas 50.0%; Ashkenazi 48.3%; Finnish 56.2%; Middle Eastern 53.0%; Amish 51.9%.
Estimated CC genotype frequency.
Global 30.5%; European 36.7%; African 12.2%; East Asian 37.1%; South Asian 33.1%; Americas 41.4%; Ashkenazi 42.4%; Finnish 37.5%; Middle Eastern 39.6%; Amish 40.3%.
Estimated CT genotype frequency.
Global 4.7%; European 5.8%; African 0.4%; East Asian 6.1%; South Asian 4.4%; Americas 8.6%; Ashkenazi 9.3%; Finnish 6.3%; Middle Eastern 7.4%; Amish 7.8%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 10/10. Source: PMID 20585626. Typical Risk.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 27117709. Typical Risk.
Cardiovascular & Metabolic
Hypertension
Systolic Blood Pressure. Evidence: 8/10. Source: PMID 33230300. Typical Levels.
Pulse Pressure. Evidence: 7/10. Source: PMID 33230300. Typical Levels.
Neurology & Mental Health
Neurodegenerative Diseases
Parkinson's Disease. Evidence: 6/10. Source: PMID 28892059. Typical Risk.
Showing effects for C/T genotype
Breast Cancer. Evidence: 10/10. Source: PMID 20585626. ~1.24x Increased Risk.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 27117709. ~1.14x Increased Risk.
Systolic Blood Pressure. Evidence: 8/10. Source: PMID 33230300. Slightly Increased.
Pulse Pressure. Evidence: 7/10. Source: PMID 33230300. Slightly Increased.
Parkinson's Disease. Evidence: 6/10. Source: PMID 28892059. ~1.09x Increased Risk.
Showing effects for T/T genotype
Breast Cancer. Evidence: 10/10. Source: PMID 20585626. ~1.54x Increased Risk.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 27117709. ~1.30x Increased Risk.
Parkinson's Disease. Evidence: 6/10. Source: PMID 28892059. ~1.20x Increased Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Presence of two copies of the C allele represents the typical genetic baseline for this locus. Large-scale genome-wide association studies show that this genetic profile does not experience the elevated risk of breast cancer associated with the T allele [1]. This protective baseline is due to the typical binding affinity of the FOXA1 transcription factor, which allows for normal expression of the neighboring TOX3 tumor suppressor gene [2]. In addition to breast cancer, this genetic profile is associated with typical systolic blood pressure and pulse pressure levels [3]. There is also no elevated risk for Parkinson's disease linked to this profile [4]. Overall, this genetic baseline represents a favorable profile across multiple health outcomes.
Typical breast cancer risk; Typical blood pressure levels; Typical risk of Parkinson's disease.
Sample genotype: CT (Heterozygous)
One copy of the T allele is linked to a moderately increased susceptibility to breast cancer [1]. This genetic variant alters a binding site for the FOXA1 transcription factor, which leads to a downstream reduction in the expression of the protective TOX3 gene [2]. Research indicates that even a single copy of this risk allele can elevate the odds of developing both estrogen receptor-positive and estrogen receptor-negative breast cancers [3]. Beyond cancer risk, this profile is associated with minor increases in systolic blood pressure and pulse pressure [4]. A slight increase in the risk of developing Parkinson's disease has also been observed in large genetic cohorts [5]. Understanding this risk can help inform personalized wellness and screening discussions with healthcare providers.
Moderately increased breast cancer risk; Slightly elevated systolic blood pressure; Slightly increased risk of Parkinson's disease.
Sample genotype: TT (Homozygous)
Two copies of the T allele are associated with the highest genetic risk of breast cancer at this locus [1]. This homozygous profile significantly enhances the binding of the FOXA1 transcription factor, which recruits repressors and markedly decreases the expression of the protective TOX3 tumor suppressor gene [2]. Clinical studies have consistently demonstrated that this genetic profile is linked to a higher risk of both estrogen receptor-positive and estrogen receptor-negative breast cancers compared to other profiles [3]. In addition to oncological risks, this profile is linked to small but measurable increases in systolic blood pressure and pulse pressure [4]. There is also a small increase in susceptibility to Parkinson's disease associated with this genetic profile [5]. These findings highlight the importance of discussing personalized risk factors and screening options with a physician.
Increased breast cancer risk; Slightly elevated systolic blood pressure; Increased risk of Parkinson's disease.
Variants with shared genetic architecture
rs3803662 · CASC16 Gene · Chr 16 · Breast Cancer Risk
rs1432679 · EBF1 Gene · Chr 5 · Breast Cancer Risk
rs4973768 · SLC4A7 Gene · Chr 3 · Breast Cancer Risk
A meta-analysis of genome-wide association studies identifies 17 new Parkinson's disease risk loci.
Identification of four novel susceptibility loci for oestrogen receptor negative breast cancer.
Content updated August 2026.
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