Q. A 10-month-old male infant presents to the pediatric clinic. His parents report that he has been increasingly irritable over the past few months, often crying inconsolably. They also note difficulties with feeding, and despite numerous formula changes, the child frequently regurgitates his meals, leading to a diagnosis of gastroesophageal reflux disease. On examination, the infant displays significant leg spasticity and frequently clenches his hands into fists. Notably, there's marked axial hypotonia. His parents are distressed as they recall him being able to smile, coo, and maintain head control, but he seems to have lost these acquired milestones. Additionally, the infant seems to have staring episodes. Laboratory evaluations reveal substantially elevated psychosine levels. Based on the clinical presentation and lab findings, what is the most likely diagnosis?