Electronegative electroretinogram in mucolipidosis IV.
OBJECTIVE
To demonstrate the progression of electroretinographic (ERG) findings in mucolipidosis IV.


METHODS
Two patients with mucolipidosis IV were examined clinically and their condition was followed up for ophthalmic manifestations of the disease. Electroretinograms were performed on both patients, and conjunctival biopsy specimens were analyzed for characteristic ultrastructural inclusion bodies using light and electron microscopy. Genomic DNA isolated from peripheral blood was screened for 2 major founder mutations in the ML4 gene using polymerase chain reaction and restriction fragment length polymorphism analyses. Haplotypes were confirmed by automated sequencing of polymerase chain reaction products.


RESULTS
In patient 1, an ERG obtained at 12 months of age showed mildly subnormal amplitude of rod-mediated and cone-mediated responses and significantly prolonged rod and cone b-wave implicit times. An ERG obtained when the patient was 6.6 years old disclosed marked progression with greater loss of b-wave than a-wave responses to rod-and-cone-mediated activity. Scotopic ERG at the highest intensity was electronegative in configuration. In patient 2, ERG showed minimal rod-mediated responses, severely subnormal cone-mediated responses, and prolonged cone b-wave implicit times. Again, electronegative configuration of the scotopic bright flash response indicated greater disturbance of b-wave generators.


CONCLUSIONS
Novel ERG findings in 2 cases of mucolipidosis IV are reported with associated clinical courses, histopathologic abnormality, and genetic studies. In both cases ERGs demonstrate an electronegative configuration, suggesting that the primary retinal disturbance in mucolipidosis IV may occur at or proximal to the photoreceptor terminals.
Pradhan
Shan M
SM
Keck School of Medicine, University of Southern California, Los Angeles, USA.
Atchaneeyasakul
La-Ongsri
LO
Appukuttan
Binoy
B
Mixon
Robert N
RN
McFarland
Trevor J
TJ
Billingslea
Andrea M
AM
Wilson
David J
DJ
Stout
J Timothy
JT
Weleber
Richard G
RG
D002648:Child; D003228:Conjunctiva / Q000648:ultrastructure; D004252:DNA Mutational Analysis; D018450:Disease Progression; D004596:Electroretinography; D005260:Female; D005500:Follow-Up Studies; D006239:Haplotypes; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics; D009081:Mucolipidoses / Q000175:diagnosis* / Q000235:genetics; D010375:Pedigree; D010775:Photic Stimulation; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology*; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012162:Retinal Degeneration / Q000175:diagnosis* / Q000235:genetics; D050053:TRPM Cation Channels; D050051:Transient Receptor Potential Channels
C416674:MCOLN1 protein, human; D008565:Membrane Proteins; D050053:TRPM Cation Channels; D050051:Transient Receptor Potential Channels