What is the probability of a sibling and daughter being a viable match for a stem cell transplant?

Probability of Siblings and Daughters Being Viable Stem Cell Transplant Donors

For siblings, there is only a 25% chance of finding a full HLA match, while for children (including daughters), the probability is significantly lower due to the inheritance pattern of HLA genes. 1

HLA Matching Requirements for Stem Cell Transplantation

• Close HLA matching is essential for successful engraftment and minimizing the risk of potentially fatal graft-versus-host disease (GVHD) 1
• The gold standard for transplantation is a high-resolution match at HLA-A, -B, -C, -DRB1, and -DQB1 loci (10/10 match) 2
• Sibling donors who are HLA-matched represent the best option for hematopoietic stem cell transplantation (HSCT) 1

Probability of Finding a Matched Sibling Donor

• There is only a 25% chance of identifying a full HLA match in a sibling donor 1
• This probability is based on Mendelian inheritance patterns of HLA haplotypes 1
• The chance of finding a matching sibling varies with family size and is higher in populations with larger families (up to 60% in some populations with larger family sizes) 3
• Age is also a factor - younger patients (0-5 years) have a lower chance (43%) of finding a matched sibling compared to adults (68%) 3

Probability of Finding a Matched Child Donor

• The probability of a child (including a daughter) being an HLA match for a parent is significantly lower than the 25% chance with siblings 2
• This is because a child inherits only one haplotype from each parent, making it impossible for a child to be a full HLA match unless the parent is homozygous for HLA or the other parent coincidentally shares HLA haplotypes 2
• In practical terms, children are more likely to be haploidentical (half-matched) donors for their parents rather than full matches 4

Alternative Donor Options When Siblings or Children Are Not Matches

• Only approximately 30% of patients have an HLA-genotypically identical sibling donor available 2
• For the remaining 70%, alternative sources include:
  • Matched unrelated donors (MUD) from registries 1, 2
  • Haploidentical donors (half-matched family members) 4
  • Umbilical cord blood units 1, 5
• In most European populations, a 10/10 matched unrelated donor can be found for at least 50% of patients, and an additional 20-30% may have a 9/10 matched donor 2
• Haploidentical transplantation with post-transplant cyclophosphamide has shown comparable outcomes to matched unrelated donor transplantation 4

Special Considerations

• Ethnic background significantly affects the probability of finding matched unrelated donors, with non-white patients having a lower chance due to genetic heterogeneity and underrepresentation in donor registries 1
• Pre-implantation HLA matching (selecting embryos that are HLA-compatible with an existing sick child) is an emerging option for families planning to have another child who could serve as a donor 5
• Umbilical cord blood allows for successful transplantation even with partial HLA mismatches, providing an alternative when no fully matched donor is available 1

Transplant Outcomes Based on Donor Type

• One-year survival rates after sibling HLA-matched cord blood stem cell transplantation can be as high as 75-90% 1
• Disease-free survival for matched sibling donor recipients can reach 72.3% versus 62.4% for alternative donors 6
• The main difference in outcomes between matched sibling and alternative donors is often related to treatment-related mortality rather than relapse rates 6