The proceedings of the 2^nd International Opsoclonus Myoclonus Ataxia Syndrome (OMAS) Symposium (Feb 6-8, 2003; Abingdon, Oxfordshire, UK) are summarized from the Neurosciences Unit, Institute of Child Health, University College, London, UK. OMAS is a rare disorder, only 10 new cases reported each year in the UK. Patients present between 6 and 36 months of age. Opsoclonus and myoclonus, are prerequisite symptoms for diagnosis. Irritability and sleep disturbance are equally disturbing accompanying symptoms, and delayed motor development, and cognitive, language and behavioral disorders are frequent sequelae. The neuroanatomical localization of OMAS is undetermined because of lack of post-mortem studies, but involvement of the brainstem and cerebellum is likely. MRI is normal in the acute stage but later may show cerebellar atrophy. A neural-crest tumor (commonly neuroblastoma) is identified in 50% of cases, but is not a presenting feature. Survival at 1 year for OMAS with neuroblastoma is better than that for patients with neuroblastoma alone. The underlying disease mechanism is probably immune mediated, but no common antibody-antigen complexes have been identified. Treatment with steroids and other immunomodulatory therapies is of some benefit, and relapse is usually precipitated by infections and reduction in steroid dose. Genetic factors in etiology need further study, in addition to environmental exposure to viral infection and the relation to neoplastic disorders. [1]

COMMENT. An autoantigen diversity in the OMA syndrome is identified in a study of the sera of 21 patients at the University of Arkansas for Medical Sciences, Little Rock, AR [2]. Ten adult patients had idiopathic OMAS, 5 adults had small cell lung cancer, and 6 pediatric patients had neuroblastoma. A brainstem cDNA library was probed to isolate target neuronal antigens, and 37 clones coding for 25 proteins were isolated. Two groups of antigens emerged: 1) proteins localized in or associated to the postsynaptic density (PSD), notably the adenomatous polyposis coli, a colorectal tumor suppressor protein highly expressed in the brainstem and cerebellum, and 2) proteins with expression or function restricted to neurons, including RNA or DNA-binding proteins and zinc-finger proteins. Frequent and heterogeneous immunity to neuronal antigens occur without a specific antibody marker of OMAS. PSD is a frequent source of novel autoantigens, and several proteins of this complex are targeted by antibodies of OMAS patients.

A cross-sectional study of known paraneoplastic antibodies in 59 children referred from various centers with moderate-to-severe OMAS and relapses, including 18 with neuroblastoma, showed that all were seronegative for anti_Hu, anti-Ri, and anti-Yo, the three antibodies most often associated with OPAS in adults. The study emphasizes the distinction between childhood OMAS and that in adults [3]. For further articles on OMAS (dancing-eye syndrome), see Progress in Pediatric Neurology III, PNB Publishers, 1997;pp332-336.