The condition rarely lets patients live for more than five years, doctors said.

The National Children's Hospital saved the two-year-old boy by transplanting stem cells from the bone marrow of his older sister.

The patient is the youngest child in a family of three siblings in the northern province of Quang Ninh. 

In 2018, the day after he was delivered at a hospital in Quang Ninh, doctors found spots of petechiae around his belly. The baby was transferred to the National Children's Hospital in Hanoi. After a week, doctors decided to discharge him as all of his health indexes were normal.

In September 2019, the boy was admitted to the Hanoi hospital again with skin haemorrhages, bloody bowel movements and low platelet counts.

Suspecting that he might have the rare genetic disorder, doctors ordered a genetic test, and found he had Wiskott-Aldrich syndrome (WAS), a condition seen only in 1-9 cases in a million children.

WAS is a disease with immunological deficiency and reduced ability to form blood clots. Signs and symptoms include easy bruising or bleeding due to a decrease in the number and size of platelets. It is caused by mutations in the WAS gene and is inherited in an X-linked manner. It primarily affects males.

Normally, a patient with WAS cannot live for more than five years, with death occurring as a result of infectious complications, brain haemorrhage or other malignancies.

The only method that can cure a WAS patient is a bone marrow transplant that transfuses hematopoietic stem cells (cells that can transform into all kinds of blood cells including white blood cells, red blood cells and platelets) from healthy people into the patient's body to replace damaged or abnormal stem cells.

Once doctors screened and found that the boy’s sister had a matching marrow source, they decided to go ahead with the hematopoietic stem cell transplantation (HSCT).

This involves the intravenous infusion of autologous or allogeneic stem cells collected from bone marrow, peripheral blood, or umbilical cord blood to re-establish hematopoietic function in patients whose bone marrow or immune system is damaged or defective.

On February 26, the HSCT was performed following the treatment regimen set by the European Society for Blood and Marrow Transplantation. Earlier, the boy had been put through one week of chemotherapy to destroy his own marrow.

Twenty-one days after the transplantation, the new marrow had grown by 87 percent in the patient’s body and all of his indexes of red blood cells, white blood cells, platelets were at normal levels.

On day 33, the new marrow had fully grown inside his body, meaning the boy had been completely cured of WAS. This is the first time ever that a WAS patient has been cured in Vietnam.

The National Children's Hospital is now treating 11 other kids with WAS. The youngest is five months old and the oldest is seven.

Le Quynh Chi, head of the immunology department at the hospital, said a successful bone marrow transplant will completely cure WAS patients, who are mostly children, allowing them to have a normal life like any other children.

However, the cost for such a transplant is high, and the health insurance covers only a small part of it.

Normally, it costs hundreds of millions of dong or up to VND1-2 billion ($42,200-84,400) in several cases, not to mention other expenditures and efforts a family must spend and make during the long period of treatment.