Rapid, progressive deterioration of vision and a
slower but progressive deterioration of the intellect. Lack of motor
control, psychotic behavior, and seizures develop later, with onset at about
10 years of age.
Gene map locus is 16p12.1-11.2.
Compared to the other forms, onset is later, at
around 10 years of age. It is characterized by rapid and progressive
deterioration of vision (because of tapetoretinal degeneration with retinal
atrophy) and slower and progressive intellectual deterioration (progressive
dementia, cerebellar disturbances, seizures, psychomotor regression,
psychosis, and brain atrophy). Prenatal diagnosis on chorionic villus
samples is possible. Accumulation of an autofluorescent lipopigment has been
found not only in the perikaryon of different neuronal cell types but also
in extraneuronal cells. Vacuolization of lymphocytes is another finding in
these patients, affecting up to two thirds of lymphocytes. Myoclonic fitting
is less prominent in the later-onset group, but dystonic posturing and
antisocial activity are more pronounced features.