Hum Genet (1993) 92:451-456 human .. gene ,cs 9 Springer-Verlag 1993 An adult-type metachromatic leukodystrophy caused by substitution of serine for glycine-122 in arylsulfatase A Koichi Honke 1, Takahiko KobayashP, Tetsuya FujiP, Shinsei Gasa ~, Mei Xu 1, Yuji Takamaru 2, Rui Kondo 3, Shoji Tsuji 3, Akira Makita ~ 1 Biochemistry Laboratory, Cancer Institute, Hokkaido University School of Medicine, Sapporo, Japan 2Department of Psychiatry, Hokkaido University School of Medicine, Sapporo, Japan 3Department of Neurology, Brain Research Institute, Niigata University, Niigata, Japan Received: 16 March 1993 / Revised: 28 April 1993 Abstract. Metachromatic leukodystrophy (MLD) is a lyso- somal storage disease with autosomal recessive inheri- tance caused by a deficiency of the enzyme arylsulfatase A (ASA). We have identified a new mutation in the ASA gene of a patient with adult-type MLD. In this mutation, the glycine at position 122, a highly conserved residue in the AS gene family, was replaced by serine. In a transient expression study, COS cells transfected with the mutant cDNA carrying 122Gly--~Ser did not show an increase of ASA activity and produced little material immunoreactive to an anti-ASA antibody, despite normal mRNA levels. Introduction Metachromatic leukodystrophy (MLD) is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of arylsulfatase A (EC 3.1.6.8, ASA) (Austin et al. 1963; Mehl and Jatzkewitz 1965). It is characterized by an accumulation of sulfatide in the white matter of the central nervous system, the peripheral nerves, the kidney, the gallbladder, and other visceral or- gans (Jatzkewitz 1958; Austin 1959). MLD is classified into three clinical phenotypes: late infantile, juvenile, and adult types based on the age of on- set and the severity of symptoms. Through extensive stud- ies, Gieselmann and his coworkers have shown a simple genotype-phenotype correlation explaining the three clin- ical phenotypes (Polten et al. 1991; Kappler et al. 1992). This concept coincides with the model for the correlation between residual enzyme activity and the turnover rate of its substrate in the lysosome (Conzelmann and Sandhoff 1983/1984; Leinekugel et al. 1992). The mutations of the ASA gene observed in MLD patients range from single Correspondence to: K. Honke, Biochemistry Laboratory, Cancer Institute, Hokkaido University School of Medicine, Kita-ku N15 W7, Sapporo 060, Japan point mutations (Fluharty et al. 1991; Gieselmann et al. 1991; Kondo et al. 1991; Polten et al. 1991; Kappler et al. 1992) to splicing alterations (Fluharty et al. 1991; Polten et al. 1991), and a deletion (Bohne et al. 1991). Expres- sion studies have revealed that mutations such as the splicing alteration and deletion result in no residual en- zyme activity, and that point mutations cause instability of the enzyme, while maintaining low residual activity. An accumulation of data on mutations in the ASA gene and the fate of the mutant ASA protein should promote our understanding of the molecular basis of the hetero- geneity of the clinical phenotypes, and should elucidate the correlation between the structure and the function of the ASA protein. In this paper, we describe a novel point mutation in the ASA gene causing adult-type MLD. Materials and methods Patient The patient was a female, with no familial history of MLD. There was no consanguinity between her parents. When she was 33 years old, she developed abnormal behavior, and later dementia that pro- gressed slowly. At the age of 37, a computed tomography scan revealed brain atrophy and low density of white matter. ASA ac- tivity toward p-nitrocatechol sulfate in leukocytes was found to be reduced to approximately 6% of the normal value, although ASB activity was equal to the normal level. She was, therefore, diag- nosed as having adult-type MLD. She subsequently developed loss of speech, quadriparesis and seizures, and died at the age of 48. Histopathology revealed typical demyelination and deposits of metachromatic granules in the central and peripheral nervous sys- tems. Chemical analysis of the brain glycolipids revealed accumu- lations of sulfatide. Materials Thermus aquaticus (Taq) polymerase was purchased from Perkin- Elmer/Cetus. [o~-32p]dCTP (specific radioactivity > 3000 Ci/mmol) was from Amersham. Sequenase Ver. 2.0 was from United States