Cord Blood Genetic Testing for Dwarfism: Our Family’s Experience
Family experience + current testing guidance
How our family used cord blood for postnatal genetic testing—and what LP families should arrange with a genetics team and laboratory before delivery.
The Short Answer
- Cord blood can provide DNA for genetic testing if the chosen laboratory accepts it and the collection is arranged before delivery.
- A purple- or lavender-top EDTA tube is accepted by some laboratories, but it is not a universal do-it-yourself protocol.
- The most informative plan usually starts by identifying the familial pathogenic variant or selecting a defined family-based assay.
- Cord blood testing is not the same as private or public cord blood banking.
- If cord blood is not collected, testing can ordinarily be performed later using peripheral blood or another specimen accepted by the laboratory.
Why This Question Mattered to Our Family
When my husband and I were planning a family, we had to think about the possibility that a child could inherit both of our skeletal dysplasias. I have achondroplasia. My husband was diagnosed with pseudoachondroplasia, although clinicians noted that some of his features resembled multiple epiphyseal dysplasia.
We encountered medical professionals who focused heavily on the genetic risks and questioned why we would try to have children. Those conversations rattled us. We listened, asked questions, sought clinicians with skeletal-dysplasia experience, and made our own decision: we wanted a family, and we wanted accurate information so we could prepare medically.
Understanding Our 25% Scenario
Achondroplasia is caused by a pathogenic variant in FGFR3. Current classification recognizes COMP-related pseudoachondroplasia as a separate autosomal dominant condition caused by a pathogenic variant in COMP. If one parent is heterozygous for an achondroplasia variant and the other is heterozygous for a COMP-related condition, the variants are in different genes and can assort independently.[1][2]
| Possible inheritance | Probability | Description |
|---|---|---|
| Neither familial variant | 25% | Does not inherit achondroplasia or the parent’s COMP-related condition. |
| FGFR3 variant only | 25% | Achondroplasia only. |
| COMP variant only | 25% | The parent’s COMP-related skeletal dysplasia only. |
| Both familial variants | 25% | Double heterozygosity. The clinical outcome cannot be predicted from the Punnett square alone. |
Why We Declined Prenatal Diagnostic Testing
Amniocentesis was available during both pregnancies. We decided against it because the result would not have changed whether we continued the pregnancy, and we did not want to accept an invasive procedure for information we could obtain after birth. That was our personal decision—not a recommendation for or against prenatal testing.
With our son, prenatal ultrasound findings strongly suggested achondroplasia. Ultrasound could not tell us with certainty whether he had also inherited his father’s condition. With our daughter, the ultrasounds did not show typical achondroplasia features. COMP-related pseudoachondroplasia is usually not apparent at birth: length and facial appearance are generally typical, with the growth rate often falling below standard curves around age two. A normal prenatal ultrasound therefore could not rule it out.[2]
How Cord Blood Genetic Testing Works
The cord blood is the specimen; it is not the test itself. The useful question is not simply “Can the OB draw a purple-top tube?” It is: Which laboratory test has been ordered, and what specimen does that laboratory require?
Meet with genetics before delivery
Confirm the clinical diagnoses, retrieve prior molecular reports if they exist, and decide exactly what the newborn will be tested for. A known familial variant often makes targeted testing faster and easier to interpret.
Choose the laboratory and assay
Ask the genetics team which laboratory will perform the test and whether it accepts fresh cord blood for that assay. If the familial variant has not been identified, the laboratory may need a broader panel, sequencing, deletion/duplication analysis, or a specifically designed family study.
Follow that laboratory’s specimen instructions
For example, GeneDx currently accepts 0.5–2 mL of cord blood in an EDTA lavender-top tube, requires it to be labeled as cord blood, and gives specific shipping instructions. Another laboratory may have different requirements. Do not substitute a generic internet checklist for the selected laboratory’s current instructions.[3]
Arrange parental samples when required
Targeted familial-variant testing, trio testing, or contamination analysis may require blood or buccal samples from one or both parents. Cord blood can contain maternal cells, so some workflows include a maternal-cell-contamination study.[4]
Put the plan in the delivery record
The OB, hospital, genetics team, and laboratory should know the plan before delivery. The correct tubes, labels, requisition, kit, handling instructions, and shipping arrangements need to be available. Collection should follow hospital procedure and should not interfere with obstetric or newborn care.
What Our Family Did
Before our daughter’s delivery, our genetics team arranged for cord blood to be collected in EDTA tubes. The goal was to learn whether she had inherited her father’s familial skeletal-dysplasia finding without putting her through a separate newborn blood draw.
Our genetics team used samples from our daughter and my husband as part of the laboratory workup. Comparing family samples can be useful within a defined method—such as targeted familial-variant testing, linkage analysis, or another validated family-based assay—but the exact method should be taken from the laboratory report rather than inferred from the blood collection itself.
The clinical result communicated to us was that our daughter had not inherited her father’s familial condition. We were not hoping for a particular result; we wanted information that could help guide her care. Using cord blood also meant one fewer needle stick for our newborn.
What Do We Know About Inheriting Both Conditions?
GeneReviews notes that children of parents with two different dominantly inherited skeletal dysplasias can inherit neither condition, either condition alone, or both, and that a double diagnosis may carry a risk of a poorer outcome. It does not provide one universal prognosis for every pairing.[1]
COMP variants can produce COMP-related pseudoachondroplasia or, in some families, autosomal dominant multiple epiphyseal dysplasia. That helps explain why a person’s clinical appearance may not perfectly match a traditional diagnostic label. It does not make pseudoachondroplasia an FGFR3 condition or make a child with achondroplasia plus a COMP-related disorder homozygous for one gene.[2]
We personally know families whose children were reported to have two dwarfism diagnoses and whose medical courses differed greatly. Those stories deserve respect, but they cannot establish whether a particular gene combination is safe or dangerous. Families need counseling based on the exact molecular findings and the limited published evidence available for that pairing.
Cord Blood Testing Is Not Cord Blood Banking
For genetic testing, a fresh or properly stored specimen is sent to a clinical laboratory so DNA can be analyzed. Cord blood banking generally refers to storing cord-blood stem cells for potential future transplantation. The decisions, costs, consent forms, handling, and evidence are different.
Our separate article discusses the broader banking decision: Cord Blood Banking: A Difficult Decision
Questions to Ask Before Delivery
- What is each parent’s exact clinical and molecular diagnosis?
- Has the familial pathogenic variant been identified?
- What exact test will be ordered for the newborn?
- Which laboratory will perform it?
- Does that laboratory accept cord blood for this test?
- What tube, volume, label, requisition, temperature, and shipping schedule are required?
- Are maternal and paternal comparison samples needed?
- Will the laboratory perform or require maternal-cell-contamination testing?
- Who is responsible for collecting, storing, and shipping the specimen?
- How will results be explained, and what follow-up is planned?
For a clearer explanation of the inheritance math, see What Are the Chances of Having a Child With Dwarfism?
Sources
- GeneReviews: Achondroplasia—FGFR3 inheritance, reproductive probabilities, and double-heterozygosity considerations.
- GeneReviews: COMP-Related Pseudoachondroplasia—COMP inheritance, current classification, testing, and overlap with autosomal dominant multiple epiphyseal dysplasia.
- GeneDx Specimen Requirements—an example of current cord-blood tube, volume, labeling, parental-sample, and shipping requirements. Requirements vary by laboratory and test.
- UPMC Clinical Genomics Laboratory: Maternal Cell Contamination—cord blood contamination considerations and comparison-sample requirements.
Have you used cord blood for postnatal genetic testing, or are you an LP couple navigating family planning? You are welcome to share your experience below. For an individual testing plan, work with a genetics professional and the laboratory before delivery.