[An adult case of probable Bassen-Kornzweig syndrome, presenting resting tremor].

We report a 53-year-old woman with probable Bassen-Kornzweig syndrome. Her parents were a consanguineous marriage. At two years of age, she developed night blindness. During her childhood she had severe diarrhea that disappeared in adulthood. At 26 years of age, she was diagnosed as having retinitis pigmentosa and her visual acuity became worse thereafter. She noted tremor in the right hand at 37 years of age, gait ataxia at 42, and developed tremor in the bilateral lower extremities at 48. On admission, bilateral visual disturbance, resting and postural tremor, moderately poor coordination, mild distal dominant sensory impairment, an absence of tendon reflex in all four extremities, moderate to severe gait ataxia, and positive Romberg sign were found. Muscle rigidity and akinesia were not observed. Intelligence and muscle power were normal and pathological reflexes were absent. Acanthocytes were found in blood. Serum chemistry showed remarkable decreases in total cholesterol (54 mg/dl, normal 180-220), triglyceride (0 mg/dl, normal 30-150), beta-lipoprotein (3 mg/dl, normal 190-500), apoA-1 protein (66 mg/dl, normal 105-184), apoA-2 protein (11 mg/dl, normal 26-46), apoB protein (0 mg/dl, normal 38-104), apoC-2 protein (1.1 mg/dl, normal 1.2-6.4), vitamin A (297 ng/ml, normal 431-1,041), and vitamin E (0.19 ng/dl, normal 0.75-1.41). While, a marked increase in PIVKA II (703 mAU/ml, normal<40) due to a decrease in vitamin K was found. She was thus diagnosed as having Bassen-Kornzweig syndrome or hypo-betalipoproteinemia. Although brain MRI was normal, single-photon emission CT (SPECT) showed mildly decreased perfusion in the left parietal cortex and right striatum. Motor nerve conduction velocities were normal, but sensory nerve action potentials were not evoked in all four extremities. Surface EMG recorded on the right radial extensor and flexor carpi muscles at rest showed a 4.5 Hz tremor. Vitamin replacement therapy with vitamin A (10,000 IU/day), E (200 mg/day), and K (10 mg/day) was initiated. Several days after treatment, amplitude of resting tremor ameliorated mildly. Clonazepam was administered (0.5 mg/day) for further treatment. After one-month of treatment, vitamin A (656 ng/ml) and E (0.39 mg/dl) levels were elevated and PIVKA II level (29 mAU/ml) decreased. Only a mild right hand tremor remained, but sensory impairment and gait ataxia were not changed. The cause of Bassen-Kornzweig syndrome is a deletion of the microsomal triglyceride transfer protein (MTP) gene. While, familial hypo-betalipoproteinemia, due to a mutation of apolipoprotein B gene, is known to show the same phenotype. Because of the patient's refusal of genetic examination, which disease she has cannot be conclusively determined. Intention tremor was reported in Bassen-Kornzweig syndrome. However, her 4.5 Hz tremor was also present at rest, which resembled resting tremor in Parkinson's disease. Pathophysiology of Bassen-Kornzweig syndrome is known to be due to hypo-vitaminosis. Decreased [18F]-dopa uptake in striatum of patients with long-term hypo-vitamin E has been reported in PET study. Mild hypoperfusion was found in the striatum of the present cases: indicating that her tremor was associated with striatonigral damage. Thus, careful observation of extrapyramidal signs is necessary in abeta- or hypo-betalipoproteinemia.