We reported a family in which two brothers and one sister out of five siblings were affected by a neurological disease showing the following clinical manifestations: 1) intellectual disturbance with relative preservation of memory and orientation probably developed on child food, 2) spastic paraparesis beginning at the age of about 20 years, 3) mild peripheral neuropathy and cerebellar sign. Their clinical courses were stereotyped, and so much the worse in elder patients. Two of them were investigated in detail. Laboratory findings including chromosomal analysis, amino acid analysis and thyroid function were normal. HTLV-1 antibody was negative. Several lymphocytes lysosomal enzymes including beta-hexosaminidase and arylsulfatase A and serum very long fatty acids were also within normal range. CT and MRI showed characteristic thinning of corpus callosum, dominant in anterior portion. However, changes in intensity of white matter in T2 weighted image were not so prominent. In the older patient, more mentally deteriorated, were demonstrated hypoperfusion in the fronto-parietal lobes by SPECT and slow wave bursts dominant in the same region by EEG. Therefore, we considered that the change of corpus callosum was hypoplasia, but not atrophy, and it may provoke dysfunction of relevant nervous system. Family cases of such clinical feature were rare. We could confirm only three families in literatures, all of them were Japanese.