The characteristic symptom of Costeff syndrome is the onset of progressively worsening eyesight caused by degeneration of the optic nerve (optic atrophy) within the first few years of childhood, with the majority of affected individuals also developing motor disabilities later in childhood.
The hallmark sign of Costeff syndrome is the deterioration of vision, resulting from degeneration of the optic nerve (optic atrophy), which begins in early childhood and worsens over time, with many affected individuals also developing motor impairments later on.