Clinical and Mutational Characterizations of Ten Indian Patients with Beta-Ketothiolase Deficiency
Beta-ketothiolase deficiency (mitochondrial acetoacetyl-CoA thiolase (T2) deficiency) is an inherited disease of isoleucine catabolism and ketone body utilization caused by ACAT1 mutations. We identified ten Indian patients who manifested with ketoacidotic episodes of variable severity. The patients showed increased urinary excretion of isoleucine-catabolic intermediates: 2-methyl-3-hydroxybutyrate, 2-methylacetoacetate, and tiglylglycine. Six patients had a favorable outcome, one died, and three developed neurodevelopmental sequela. Mutational analysis revealed a common (p.Met193Arg) and four novel (p.Ile323Thr, p.Ala215Asn, c.1012_1015dup, and c.730+1G>A) ACAT1 mutations. Transient expression analyses of wild-type and mutant cDNA were performed at 30, 37, and 40°C. A p.Ile323Thr mutant T2 was detected with relative enzyme activity and protein amount of 20% and 25%, respectively, compared with wild type at 37°C; it was more prevalent at 30°C but ablated at 40°C. These findings showed that p.Ile323Thr had a significant residual T2 activity with temperature-sensitive instability. Neither residual enzymatic activity nor mutant T2 protein was identified in p.Met193Arg, p.Ala215Asn, and c.1012_1015dup mutations using supernatants; however, these mutant T2 proteins were detected in insoluble pellets by immunoblot analysis. Expression analyses confirmed pathogenicity of these mutations. T2 deficiency has a likely high incidence in India and p.Met193Arg may be a common mutation in the Indian population.
KeywordsACAT1 Beta-ketothiolase deficiency Expression analysis Ketoacidosis Mutations T2 deficiency
Succinyl-CoA:3-oxoacid CoA transferase
Mitochondrial acetoacetyl-CoA thiolase
The authors thank the Cultural Affairs and Missions Sector, Egyptian Ministry of Higher Education, for providing a scholarship to study beta-ketothiolase deficiency. The authors also thank N. Sakaguchi for her indispensable technical assistance.
This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan [grant numbers 26114708, 24591505, 16K09962, 15K01693]; Health and Labour Science Research Grants for Research on Intractable Diseases from the Ministry of Health, Labour and Welfare of Japan; and the Practical Research Project for Rare/Intractable Diseases from Japan Agency for Medical Research and Development (AMED).
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