Is Rheumatoid Arthritis Hereditary? The Polygenic Answer for IVF Families

Rheumatoid arthritis is a parent's morning stiffness, the rotation of DMARDs on the kitchen counter, the two-month rhythm of rheumatology appointments, and the slow recalibration of what a good day looks like.

Yes, RA runs in families, but not the way a single-gene disease does. Women have a lifetime risk of developing RA of about 3.6 percent; men about 1.7 percent (Crowson 2011). Twin studies place the overall genetic contribution at roughly 53 to 65 percent (MacGregor 2000; Svendsen 2013); the rest is environment, immune biology, and chance. Because RA is polygenic rather than Mendelian, first-degree relatives of someone with RA carry materially elevated lifetime risk (Smolen 2018), and no family history predicts a specific child's outcome.

For IVF families with RA in the picture, that polygenic structure is the part that changes the decision. Each embryo from the same parents inherits a different mix of the variants that drive RA risk. That's the only place a transfer decision can actually do any work. It's a different question from the family-history conversation the adults have already had.

What rheumatoid arthritis actually takes

RA begins in the small joints of the hands and feet and moves symmetrically to larger joints over time, bringing morning stiffness that can last hours and a base layer of fatigue that recalibrates what a full day looks like. The first-line treatment is methotrexate plus short-course steroids, with biologic or targeted synthetic DMARDs added if that combination isn't enough (Fraenkel 2021). "Works" in this context means slowing joint damage and holding symptoms down, not curing.

At the population level, RA is associated with roughly a 5-year reduction in life expectancy compared to the general population (Chiu 2021). That's an average across cohorts, severities, and treatment eras, not a prediction for any one person, and not a prediction for any one child. It does explain why the hereditary question isn't rhetorical for someone planning a family around an RA diagnosis.

Biologically, RA is an immune dysregulation: the system produces autoantibodies that target proteins in the joint lining, and chronic inflammation erodes cartilage and bone over time.

Which raises the question. If RA costs this much, how much of that cost is actually handed down inside a family?

Hereditary isn't the same as determined

Twin studies are where the calibrated answer comes from. MacGregor's 2000 UK cohort put the heritability of RA at 53 percent, with a 95 percent confidence interval of 40 to 65. Svendsen's 2013 Danish twin study put it at 65 percent, with a 95 percent confidence interval of 50 to 70. Those are the standard pair; they bracket a range, not a single headline number. Most of why one person develops RA and another doesn't is written into their DNA before birth. The remainder is environmental exposure, immune biology, and chance.

The biggest single contributor to that genetic majority is a region called HLA-DRB1, which accounts for roughly 20 percent of the total genetic risk for RA (Gao 2024). That's a large effect for a single locus. It can make RA sound, for a minute, like it's almost a single-gene disease. It isn't. HLA-DRB1 is the first chapter. PTPN22 and PADI4 are established additional contributors, and the rest of the genetic signal is distributed across many smaller-effect variants scattered throughout the genome. Each one on its own does very little. Together, they add up to most of the genetic story.

That structure is what "polygenic" means in practice. And it matters in two ways a family-history conversation alone doesn't capture.

The first is heterogeneity within RA itself. The disease comes in a seropositive form (defined by anti-citrullinated protein antibodies and rheumatoid factor) and a seronegative form. They look clinically similar but differ genetically, and as Smolen's 2018 review documents, a single heritability number doesn't apply uniformly to both. Any honest hereditary answer for a given family is conditional on which version is running in it.

The second is where the embryo question lives. Because the genetic contribution is spread across many variants, the reshuffling that happens when two parents make an embryo isn't a coin flip on one gene. Two embryos from the same parents inherit different mixtures of those risk variants, and those different mixtures produce different baseline risks. The question stops being "is RA in this family" and becomes "which specific embryo in this cycle is carrying more or less of the inherited signal."

What this changes for IVF families

Here's what polygenic embryo screening involves, concretely. A few cells are biopsied from each embryo at the blastocyst stage of a standard IVF cycle. The DNA from that biopsy is sequenced, and a risk estimate is computed for each embryo across a panel of polygenic conditions. The full form of the procedure is preimplantation genetic testing for polygenic conditions, usually written PGT-P, and it runs off the same sample that chromosomal screening does, so it doesn't add a separate biopsy. Different polygenic conditions are predicted with different degrees of confidence; none of them are predicted with certainty.

For a family with RA in it, the first thing this changes is that family history stops being the entire input. Herasight incorporates family history directly into how a polygenic risk estimate gets interpreted, because if a parent has RA, the baseline risk for a child isn't the same as the general-population baseline that a raw polygenic score alone is built against. That integration is part of what makes the embryo-level risk number for this family useful.

The methodology question underneath all of this is whether a polygenic score built from population-scale genetic studies actually distinguishes between siblings from the same family. Herasight validates its polygenic scores on sibling pairs, which is the right comparison when the decision is among embryos from the same parents. That's a methodology claim about how the scoring is tested, not a promise that every trait performs identically within families.

The general PGT-P method is relevant to rheumatoid arthritis because RA is polygenic and because family history is already being factored in. Whether RA is part of the current screening panel, and how much it should weigh against other factors in a given transfer decision, is a conversation with Herasight's counselors. That conversation is how the generic relevance of the method becomes a specific answer for a specific family.

Scope matters. Polygenic screening can shift the risk distribution across the embryos in a given cycle. It doesn't prevent RA, doesn't read environmental exposure like smoking or dental hygiene, and doesn't replace clinical workup for anyone in the family who already has the disease.

The polygenic answer is the actionable part of the hereditary question. It isn't whether RA runs in families; you already have enough evidence for that. It's how much of that inherited risk is distributed differently across the embryos in a specific IVF cycle, and what careful handling of that looks like in a transfer decision. If you want to see what that looks like for your family, reach out to one of Herasight's counselors; that's the conversation where the general becomes your specific.