From MedlinePlus Genetics
CLN3 disease is an inherited disorder that primarily affects the nervous system. After 4 to 6 years of normal development, children with this condition develop vision impairment, intellectual disability, movement problems, speech difficulties, and seizures, which worsen over time.

In children with CLN3 disease, problems with vision often begin between the ages of 4 and 8 years. Vision impairment is caused by a breakdown of the light-sensitive tissue at the back of the eye (retinal degeneration), which worsens with age. People with CLN3 disease are often blind by late childhood or adolescence. Also around age 4 to 8, children with CLN3 disease start to fall behind in school. They have difficulty learning new information and lose previously acquired skills (developmental regression), usually beginning with loss of the ability to speak in complete sentences.

Seizures and movement abnormalities often develop in adolescence in people with CLN3 disease. These abnormalities include muscle rigidity or stiffness, clumsiness, slow or diminished movements (hypokinesia), and a stooped posture. Over time, affected individuals lose the ability to walk or sit independently and require wheelchair assistance. Rarely, people with CLN3 disease develop a distorted view of reality (psychosis) or false perceptions (hallucinations). Some affected individuals have an abnormal heart rhythm (arrhythmia) later in life. Most people with CLN3 disease live into early adulthood.

CLN3 disease is one of a group of disorders known as neuronal ceroid lipofuscinoses (NCLs), which may also be collectively referred to as Batten disease. All these disorders affect the nervous system and typically cause worsening problems with vision, movement, and thinking ability. The different NCLs are distinguished by their genetic cause. Each disease type is given the designation "CLN," meaning ceroid lipofuscinosis, neuronal, and then a number to indicate its subtype.  https://medlineplus.gov/genetics/condition/cln3-disease