Ethan, a 12-year-old boy, presents to the clinic with progressive muscle weakness, clumsiness, and difficulty walking. His parents report frequent falls and poor coordination, along with complaints of tingling sensations in his hands and feet. He also has fatty, foul-smelling stools, poor growth, and struggles with night vision. A peripheral blood smear reveals thorny red blood cells. Laboratory tests show vitamin E deficiency, extremely low serum cholesterol and triglyceride levels. Which of the following is considered a hallmark feature of this disease?
