Can two siblings both have NKH?

Because nonketotic hyperglycinemia is inherited in an autosomal recessive pattern, it can affect more than one child in the same family. When both parents are carriers, each pregnancy has a 25 percent chance of a child with NKH, a 50 percent chance of a child who is a carrier, and a 25 percent chance of a child who neither has the condition nor carries it. Those odds are the same with every pregnancy.

That's exactly what happened in the O'Sullivan family. Drake was diagnosed in 2016. In 2019, Vivian was born and diagnosed with NKH within hours. Their three older siblings, Birkley, Harper-Kate, and Rayph, do not have NKH.

Having two children with NKH doubled the family's daily care, but it also shaped the trial. The family has described it as the first sibling study for an NKH gene therapy, which means Drake and Vivian would receive treatment as part of the same trial.

Families with questions about recurrence risk should speak with a genetic counselor. If you'd like to help two siblings reach treatment together, give to the trial or share their story.

Sources: MedlinePlus Genetics: Inheritance patterns · MedlinePlus Genetics: Nonketotic hyperglycinemia