beta-Ketothiolase deficiency with favourable evolution

2-methylacetoacetyl-coenzyme A thiolase (beta-ketothiolase) deficiency: one disease - two pathways

Background

2-methylacetoacetyl-coenzyme A thiolase deficiency (MATD; deficiency of mitochondrial acetoacetyl-coenzyme A thiolase T2/ “beta-ketothiolase”) is an autosomal recessive disorder of ketone body utilization and isoleucine degradation due to mutations in ACAT1.

Methods

We performed a systematic literature search for all available clinical descriptions of patients with MATD. Two hundred forty-four patients were identified and included in this analysis. Clinical course and biochemical data are presented and discussed.

Results

For 89.6% of patients at least one acute metabolic decompensation was reported. Age at first symptoms ranged from 2 days to 8 years (median 12 months). More than 82% of patients presented in the first 2 years of life, while manifestation in the neonatal period was the exception (3.4%). 77.0% (157 of 204 patients) of patients showed normal psychomotor development without neurologic abnormalities.

Conclusion

This comprehensive data analysis provides a systematic overview on all cases with MATD identified in the literature. It demonstrates that MATD is a rather benign disorder with often favourable outcome, when compared with many other organic acidurias.

The clinical phenotype and outcome of mitochondrial acetoacetyl-CoA thiolase deficiency (beta-ketothiolase or T2 deficiency) in 26 enzymatically proved and mutation-defined patients

Mitochondrial acetoacetyl-CoA thiolase (T2 enzyme) deficiency (MIM 203750) is an autosomal recessive disorder of isoleucine and ketone-body metabolism. We determined the molecular basis of T2 enzyme deficiency in 26 patients at the levels of skin fibroblast enzyme activity, protein integrity, and DNA nucleotide sequence. Thirty different disease-associated alleles were identified. From these data we predicted that T2 in 6 of the 26 patients would have a mild effect on the enzyme protein and 20 would have a severe effect from their mutant genotypes. The corresponding clinical data were collected (by interviews and questionnaires) for the patients in the two groups. We found that genotype does not predict clinical severity and mutant sibs can have different clinical phenotypes; there were no consistent differences in clinical severity between patients with null-conferring or residual-conferring genotypes for T2 activity; only the absence of or a low urinary excretion of tiglyglycine during ketoacidosis correlated with a mild genotype. In general, T2 deficiency has a favorable outcome and 23 of 26 patients developed normally; one died during the first ketoacidotic episode and two have developmental delay. The median age at onset for the first ketoacidotic episode is 15 months (range 3 days to 48 months). The frequency of attacks falls with age, the last in our series occurring at 10 years of age; 11 patients had only one episode and 3 patients had none. We conclude that clinical consequences of T2 deficiency are avoidable with early diagnosis, appropriate management of ketoacidosis, and modest protein restriction.

Mitochondrial encephalopathies

Although no single neurological manifestation is specific of mitochondrial encephalopathies, several neurological syndromes are clearly suggestive of the diagnosis. Muscle biopsy for histochemicals, biochemical, and mitochondrial DNA studies is frequently necessary to establish diagnosis of mitochondrial encephalopathy presenting with such neurological syndromes. Mitochondrial encephalopathies most frequently result from nuclear gene defects and biochemical studies are frequently helpful in reaching a specific diagnosis. Various therapeutic interventions are beneficial in selected cases.

Molecular, biochemical, and clinical characterization of mitochondrial acetoacetyl-coenzyme A thiolase deficiency in two further patients

The molecular basis of mitochondrial acetoacetyl-CoA thiolase (T2) deficiency was studied in two patients (GK11 and GK16). Fibroblasts from each patient had detectable immunoreactive T2 polypeptide (CRM). In pulse-chase experiments, fibroblasts from GK11 had two types of CRM: one (type I CRM) disappeared after a 24-hr chase and migrated more slowly than that of the normal control; the other (type II CRM) was detected with a small amount even after a 72-hr chase and had normal electrophoretic mobility. GK16's fibroblasts had a CRM (type III) which was also detectable even after a 72-hr chase and showed a slower mobility than type I CRM. By analyzing amplified cDNA and genomic fragments, we showed that both patients are genetic compounds; GK11 for the mutations N158D and T297M, and GK16 for the mutations A301P and IVS8 (+1). Expression analyses confirmed that mutant T2 subunits with N158D, T297M, and A301P correspond to type I, II, and III CRM, respectively. Among them, only the mutant T2 polypeptide with T297M appeared to have a detectable residual activity, in spite of its instability. Cotransfection of two cDNAs containing N158D and T297M suggested that heterotetramer formation reduces residual activity in GK11 cells.

3-Ketothiolase deficiency: a review and four new patients with neurologic symptoms

3-Ketothiolase deficiency (3KTD) manifests with intermittent acidosis and is due to deficiency of mitochondrial 2-methylacetoacetate thiolase. Only 22 patients have been previously reported. Although its variable clinical presentation is recognized, the associated neurological findings have not been detailed. We report four new patients all with significant neurological symptoms. Three patients were examined with MRI of the brain which showed increased T2 intensity within the posterior lateral part of the putamen bilaterally. In two the MRI was otherwise normal; in one delayed myelination was also seen. These MRI putaminal findings may be typical enough to suggest the diagnosis of 3KTD. Two of the three had abnormal EEGs; one had an abnormal VEP. 3KTD can thus occur as an organic acidemia associated with encephalopathy.

Mitochondrial 2-methylacetoacetyl-CoA thiolase deficiency: an inborn error of isoleucine and ketone body metabolism

A review is presented of 22 published cases of verified or probable mitochondrial 2-methylacetoacetyl-CoA thiolase deficiency, a disorder of isoleucine and ketone body metabolism. The clinical expression, characterized by ketoacidosis, vomiting and lethargy, is highly variable. Typical age of onset is between 6 and 24 months. The disorder, which has been observed in several ethnic groups, is apparently inherited as an autosomal, recessive trait. The prognosis is relatively good if acute episodes of ketoacidosis and dehydration are adequately treated. There is abnormal urinary excretion of 2-methyl-3-hydroxybutyric acid, tiglylglycine, and in some instances also 2-methyl-acetoacetic acid. However, such a pattern of organic aciduria has also been found in cases with normal thiolase activity. Genetic complementation analyses have demonstrated considerable heterogeneity. The cDNA for human methyl-acetoacetyl-CoA thiolase has been cloned and sequenced. Studies in one patient showed a G-to-A substitution at position 1138 of the mRNA, causing 347Ala to Thr change in the mature enzyme. Studies in other patients have shown variable enzyme amount and/or stability.