Congenital amegakaryocytic thrombocytopenia (MPL-related)

CAMT is usually noticed soon after birth. A baby may have bruising, tiny red or purple spots on the skin (petechiae) or other bleeding, and a blood count shows very few platelets. NIH's rare-disease center says the diagnosis is usually made by 1 month of age. But in about a quarter of children in one large study, low platelets were not found at birth.

A hematologist, a doctor who treats blood diseases, usually leads the testing. A bone marrow sample shows few or no megakaryocytes, the cells that make platelets. A blood test usually finds a very high level of thrombopoietin, the signal that tells the marrow to make platelets. Genetic testing then looks for changes in both copies of the MPL gene. Finding them confirms the diagnosis. Genetic results can take a few days to weeks.

The genetic answer matters. In a few children, platelets rose for a short time after immunoglobulin or steroid treatment, which at first pointed doctors toward the wrong diagnosis. Changes in a different gene, THPO, can cause a look-alike condition. In one family with THPO changes, a medicine called romiplostim raised blood counts in all three affected children. The researchers noted that a transplant is not expected to work for that form.

Platelet transfusions and other measures help control bleeding while diagnosis and longer-term care are arranged. Additional blood-product and infection support may be needed if other blood counts fall.

Allogeneic transplantation is the established definitive treatment for the blood-production defect in MPL-related CAMT. The transplant team weighs the disease course against graft failure, infection, conditioning toxicity and graft-versus-host disease.

A matching related or unrelated donor can be used. The choice of graft and conditioning depends on the child, the donor and center experience. Published outcomes from small or retrospective cohorts cannot guarantee an individual result.

When a transplant from a donor is planned, the team usually tests brothers and sisters first. Each full sibling has about a one in four chance of being a full match.

Most patients do not have a matched relative. In the words of NMDP, the U.S. registry, “75% of patients don’t have a fully matched donor in their own family.” The team then searches registries of volunteer donors around the world and banks of donated cord blood. In some transplants, a half-matched parent, child or sibling can also be the donor.

Matching depends on inherited tissue markers called HLA, so a patient is most likely to match someone who shares their ancestry. Every person who joins makes the search a little more likely to succeed, especially for patients from groups that are underrepresented on registries.

Without a transplant, MPL-related CAMT usually leads to failure of all blood-cell production. This often happens in early childhood. In a study of 56 people with gene-confirmed CAMT, about 3 in 4 of the children whose marrow failed were younger than 4. The pace depends partly on how much the gene changes weaken the receptor, so some children stay stable longer than others.

A donor transplant is the only treatment known to cure the blood problem. In registry studies, most children were alive years after transplant. Children did best with a well-matched donor, whether a brother or sister or an unrelated volunteer. Graft failure is a real risk. That is when the donor cells do not take hold or stop working, and some children need a second transplant.

Bleeding before transplant also shapes the long-term picture. In the same study, bleeding in the brain happened only before birth, at birth or in the first 4 weeks of life. Those bleeds can have lasting effects that a transplant does not reverse. These group numbers describe children who had transplants. They cannot predict one child's future.