Cord Blood for Dwarfism Genetic Testing
Cord Blood for Dwarfism Genetic Testing
How LP couples can use cord blood to test for double dominancy — the method, the limitations, and what to expect.
When my husband and I were planning to get pregnant, there was the question of double dominancy for heterozygous dwarfism. My husband has pseudoachondroplasia and I have achondroplasia. We were told why take the risk and even TRY for children if there is a chance of health issues or being incompatible with life.
And we felt — why not try? Don’t get me wrong. Talking to our geneticist and OB/GYN definitely got us rattled. But I was determined to find the answers. In my own research, I found a handful of people with both the pseudo and achon genes who are living productive, healthy lives. Most of them had only a couple of health problems — fewer than our son, who only has one dwarfism gene. I interviewed LP adults who were either carriers of both genes or whose child was a carrier of both genes. All of them said they had the same common surgeries as pseudos or achons individually.
By the time we got pregnant, I distinctly remember a young genetic counselor having a serious talk with us about our pregnancy. She had a solemn look on her face as she went over the Punnett square. We smiled and told her we already knew the probabilities. Coincidentally, our childhood geneticist walked in to consult with us. When she entered the room, she smiled and assured the counselor: “They know their stuff.”
Why We Chose Cord Blood Over Amnio
We could have had amniocentesis done with both children, but we felt the risk to the baby was too high. And the deeper question was: what would we do with that information? Ending the pregnancy was out of the question. We decided we would deal with whatever came once the babies were born.
With our son, the ultrasound results showed he was definitely achondroplastic — the characteristic head shape, trident hands, and limb proportions were clear. But we weren’t sure if he also had the pseudo gene. We didn’t investigate further in utero.
With our daughter, her ultrasounds didn’t show achon features. But we knew that pseudoachondroplasia typically does not present radiologically until age 2–3 — which was when my husband himself was diagnosed. So we couldn’t rule it out from the ultrasound alone.
When I gave birth to our daughter, we saved cord blood specifically to run the genetic test. We asked our OB to pull purple-top tubes from the cord blood immediately after delivery — before the cord was discarded.
Rather than testing for the COMP gene directly, our geneticist recommended matching the cord blood against my husband’s blood sample — since he doesn’t present with classic pseudoachondroplasia features (as noted by Dr. Jacqueline Hecht, he more closely resembles Multiple Epiphyseal Dysplasia in height and hand features). Direct matching against his blood was more accurate than searching for the generic COMP gene marker.
There was no match. Our daughter did not inherit the pseudo gene. We didn’t approach the test with any particular outcome in mind — we just wanted to know without subjecting our newborn to a blood draw. The cord blood was already being collected. One less poke for our baby.
Is Heterozygous Dwarfism High Risk?
Some geneticists experienced in dwarfism say that heterozygous dwarfism — inheriting two different dominant genes, like achondroplasia and pseudoachondroplasia — is considered high risk (more health complications, possibility of stillbirth). Others say it is not a definitive risk. The honest answer is that the medical literature is limited and geneticist opinions vary.
I know of children with two different dwarfism genes. One is living and healthy. Another had many health complications and passed before the age of five — though I never learned the cause of death from that parent, who was a close friend of mine and who herself passed unexpectedly within the year.
From talking to geneticists on the LPA Medical Advisory Board and those who have followed us throughout our lives, MED and pseudoachondroplasia have similar genetic traits. Whether that would be considered homozygous or heterozygous dwarf genes in our specific case is a nuanced question. My husband does not resemble the classic pseudo presentation — which is why we matched our children’s blood directly against his rather than searching for the COMP gene.
What Would You Do With That Information?
There are several means of determining whether a child has dwarfism — amniocentesis, prenatal ultrasound, postnatal blood draw, or cord blood testing as described here. But the deeper question that every LP family must answer for themselves is: what would you do with that information?
For us, the answer was simply that we wanted to know — not to change anything, but to be medically prepared. Using cord blood was the safest and most practical path to that answer without any additional risk to our newborn.
Have you used cord blood for genetic testing with your LP child? Or are you an LP couple navigating the family planning conversation right now? Share your experience in the comments — this is one of the most personal topics on this site and every perspective adds value.
The risks for a child with both achondroplasia and pseudochondroplasia depends on the type of pseudochondroplasia, from what I’ve read. Pseudochondroplasia can be caused by a mutation in the same gene as achondroplasia, or a completely different gene. A child who has achondroplasia and pseudochondroplasia coded by the same gene will have double dominant issues, while a child who has both conditions coded for by two different genes will just have features of both put together and will be about as healthy as someone with only one of those conditions.