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Neurology 2000;55:99-104
© 2000 American Academy of Neurology

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Articles

Central and peripheral nervous system dysfunction in the clinical variation of Salla disease

T. Varho, MD, S. Jääskeläinen, MD, PhD, U. Tolonen, MD, PhD, P. Sonninen, MD, L. Vainionpää, MD, PhD, P. Aula, MD, PhD and M. Sillanpää, MD, PhD

From the Departments of Medical Genetics (Drs. Varho and Aula), Pediatric Neurology (Drs. Varho and Sillanpää), Clinical Neurophysiology (Dr. Jääskeläinen), and Diagnostic Radiology (Dr. Sonninen), University of Turku; and Departments of Clinical Neurophysiology (Dr. Tolonen) and Pediatrics (Dr. Vainionpää), Oulu University Hospital and Department of Medical Genetics, University of Helsinki (Dr. Aula).

Address correspondence and reprint requests to Dr. Tarja Varho, Department of Medical Genetics, University of Turku, Kiinamyllynkatu 10, FIN-20520 Turku, Finland.

OBJECTIVE: To evaluate the degree of possible peripheral nervous system (PNS) involvement in addition to CNS manifestations in Salla disease, a free sialic acid storage disorder leading to severe mental retardation with a wide clinical variation.

BACKGROUND: Salla disease is a lysosomal storage disorder that affects the white matter of the CNS. MRI findings and recent ¹H MRS study results provide evidence for delayed central myelination, but there is no previous evidence for PNS involvement in this disease. The gene coding for a presumptive sialic acid transport protein has recently been identified, and the first disease-causing mutations have been characterized.

METHODS: Nerve conduction studies; evoked potentials to visual (VEP), brainstem auditory (BAEP), and somatosensory stimuli (SEP); and EEG were carried out on 22 patients (age range 2 months to 57 years) with biochemically and genetically confirmed Salla disease. Brain MRI were available on 14 patients.

RESULTS: Nerve conduction studies revealed abnormalities in nearly half of the patients (10/21). The four severely disabled patients and the oldest patient had greatly reduced nerve conduction velocities and prolonged distal latencies compatible with demyelinating polyneuropathy. In addition, SEP was abnormal in the majority of the patients, but VEP and BAEP in only a few cases. PNS involvement was clearly associated with both the phenotypic severity and MRI findings.

CONCLUSIONS: The results indicate that dysmyelination in Salla disease occurs not only in the CNS but also in the peripheral nervous system, contributing to the phenotypic variation, which can now be correlated with the molecular basis of the disease.

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