[A case of Gerstmann-Sträussler-Scheinker syndrome (GSS) with late onset--a haplotype analysis of Glu219Lys polymorphism in PrP gene].

We report a 74-year-old man with late onset Gerstmann-Sträussler-Scheinker syndrome (GSS). In this family, 3 out of 6 siblings and his father developed cerebellar ataxia and mental deterioration in their fifth decades. He complained of unsteady walking and tingling pain in the legs at the age of 70. Neurological examination revealed moderate truncal ataxia, mild limb ataxia, ataxic speech, sensory impairment, paresthesia and areflexia in the lower extremities. CSF examination showed elevated CSF and 14-3-3 proteins with a normal cell count. EEG and brain MRI demonstrated no abnormality. Somatosensory evoked potential (SEP) study showed delayed N13-N20 interpeak latencies in the upper extremities and delayed N20 at 12th thoracic spinous process, indicating dysfunction of the posterior roots or columns of the spinal cord including the dorsal horns and proximal peripheral nerve. Analysis of the prion protein gene demonstrated a Pro102Leu amino acid substitution, which is compatible with classical GSS. Haplotype analysis of the PrP gene identified a Glu219Lys polymorphism on another allele. Recently, it was confirmed that protein X, which accelerates the conversion of the normal type of PrP (PrPC) into a pathological type of PrP (PrPSc), binds to the 219th amino acid residue of PrP. Therefore, the 219Lys polymorphism theoretically inhibited formation of PrPSc and may thus have delayed the onset of the disease in this patient.