This clinical trial is focused on studying the long-term safety of a treatment for Generalized Myasthenia Gravis, a chronic autoimmune disease that causes muscle weakness. The treatment being tested is called efgartigimod, which is administered in two forms: intravenously (through a vein) and subcutaneously (under the skin). The study aims to evaluate how safe and well-tolerated these forms of efgartigimod are when given to children with this condition.

Participants in the study will receive either the intravenous or subcutaneous form of efgartigimod over a period of time. The study will monitor the occurrence and severity of any side effects, as well as changes in laboratory test results, vital signs, and other health indicators. The study will also look at the presence of any antibodies that might develop against efgartigimod or the enzyme used in the subcutaneous form, known as recombinant human hyaluronidase PH20.

The purpose of this study is to ensure that the treatment is safe for long-term use in children with Generalized Myasthenia Gravis. By carefully observing the effects of the treatment, researchers hope to gather important information that could lead to better management of this condition in the future.