Hyperlysinemia

Hyperlysinemia is an inherited condition that is characterized by elevated blood levels of lysine, which is one of the building blocks (amino acids) of proteins. Amino acids are not stored in the body and must be broken down when they are no longer needed. When the body's ability to break down lysine is impaired, lysine can build up and cause hyperlysinemia. Hyperlysinemia is classified as either type I or type II, depending on which steps of lysine breakdown are interrupted. 

The signs and symptoms of hyperlysinemia can vary widely, even among members of the same family. The features that have been reported in people with hyperlysinemia have included short stature, speech and language delays, intellectual disabilities, behavioral abnormalities, abnormal muscle stiffness (spasticity), and seizures. However, some researchers have suggested that as many as half of all people with hyperlysinemia are asymptomatic, which means that they do not have any signs or symptoms of the disorder. These people may not even be aware that they have the condition.

Because the signs and symptoms of hyperlysinemia can vary and because hyperlysinemia is very rare, it is difficult for researchers to determine whether these features are caused by the condition itself or by other factors. 

People with a condition called 2,4-dienoyl-CoA reductase (DECR) deficiency may also have hyperlysinemia. Additional features of DECR deficiency may include an inability to grow and gain weight as expected (failure to thrive), developmental delays, abnormal brain function (encephalopathy), and eye abnormalities such as degeneration of the nerves that carry information from the eyes to the brain (optic atrophy).