Inheritance: autosomal recessive. A sibling may be affected.
Gene affected: CLN3 on 16p11.2 (usually a 1.02 kb deletion)
Most patients are homozygous for the affected gene but some patients are heterozygous, suggesting that another gene may be involved. A patient who is heterozygous for the mutation tends to show a slower progression.
Age at onset: <= 10 years of age
Clinical findings may include:
(1) visual loss with a fundoscopic exam that may:
(2a) be normal
(2b) show bull's eye maculopathy
(2c) show pigmentary and/or atrophic change
(2) cognitive decline
(3) behavioral changes
(4) progressive motor disturbances
(5) seizure disorder
A patient experiencing visual loss will have a number of changes in the electroretinogram (ERG), as described in Chapter 19.
Laboratory findings
(1) presence of vacuolated lymphocytes in the peripheral blood smear
(2) electron microscopy shows the vacuoles to be "fingerprint" inclusions
