Background: Neurocognitive disorders affect how the brain uses oxygen. They may affect mental development in children. These disorders can be studied with imaging scans that use radiation; however, these methods are not ideal for research on children. Two technologies-functional near-infrared spectroscopy (fNIRS) and diffuse correlation spectroscopy (DCS)-use light to detect changes in brain activity. These methods are safer, and they can be used in a more relaxed setting. In this natural history study, researchers want to find out whether fNIRS and DCS can be a good way to study people with neurocognitive disorders.

Objective: To find out whether fNIRS and DCS can be useful in measuring brain activity in people with neurocognitive disorders.

Eligibility: People aged 6 months or older with neurocognitive disorders. These can include Niemann-Pick disease type C1 (NPC1); creatine transporter deficiency (CTD); Smith Lemli Opitz syndrome (SLOS); juvenile neuronal ceroid lipofuscinosis (CLN3 disease); and Pheland-McDermid (PMS) syndrome. Healthy volunteers are also needed.

Design: Participants will have a physical exam. They will have tests of their memory and thinking. Participants will sit in a quiet room for the fNIRS and DCS tests. A snug cap (like a cloth swim cap) will be placed on their head. The cap has lights and sensors. Another sensor will be placed on their forehead. Participants will perform tasks on a computer. This testing will take 45 to 60 minutes. The tests will be repeated within 1 to 4 weeks. Participants will be asked to return for repeat tests 1 year later....