A 1-year-old girl became the youngest lung transplant recipient in Japan on Thursday after being given the organs from a brain-dead boy, according to a hospital in Okayama Prefecture that performed the surgery.

The girl suffers from pulmonary hypertension, or high blood pressure in the lungs, that particularly affects the blood vessels that supply them. If the lung arteries and capillaries are too narrow or become blocked, it could eventually cause the heart muscle to weaken and fail.

Okayama University Hospital said the girl had been on a respirator in an intensive care unit since developing breathing difficulties shortly after birth. Because her condition did not improve despite treatment, she was registered with a transplant coordination group in February to receive organs.

The Japan Organ Transplant Network said the donor boy was under 6 years old and was declared brain dead Wednesday at a hospital in neighboring Hiroshima Prefecture. He had developed cerebellar hemorrhage and his family agreed to donate his organs.

In Japan, organs can be donated from brain-dead people regardless of age as long as the family consents, unless the individuals have expressed a desire not to donate them, based on the revised organ transplant law that took effect in 2010.

However, stricter brain death criteria are applied to children younger than 6 because their brains are believed to have a strong ability to recover.