Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by a deficiency of arylsulfatase A. MLD is a heterogeneous disease with variable age at onset and variable clinical features. We evaluated a 33-year-old female patient who developed manifestations of disinhibitory behavior. She was diagnosed with MLD by genetic analysis, which revealed compound heterozygous ARSA missense mutations (p.G99D and p.T409I). The same combination of mutations was previously reported in a Japanese patient with similar symptoms. We performed additional, detailed neuropsychological tests with functional imaging on the current patient that demonstrated frontal lobe dysfunction. These results indicate that the mutations have important implications for genotype–phenotype correlation in MLD.