Delayed-onset dystonia associated with 3-oxothiolase deficiency

A Proposed Diagnostic Algorithm for Inborn Errors of Metabolism Presenting With Movements Disorders

Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.

Beta-Ketothiolase Deficiency Presenting with Metabolic Stroke After a Normal Newborn Screen in Two Individuals

Beta-ketothiolase (mitochondrial acetoacetyl-CoA thiolase) deficiency is a genetic disorder characterized by impaired isoleucine catabolism and ketone body utilization that predisposes to episodic ketoacidosis. It results from biallelic pathogenic variants in the ACAT1 gene, encoding mitochondrial beta-ketothiolase. We report two cases of beta-ketothiolase deficiency presenting with acute ketoacidosis and "metabolic stroke." The first patient presented at 28 months of age with metabolic acidosis and pallidal stroke in the setting of a febrile gastrointestinal illness. Although 2-methyl-3-hydroxybutyric acid and trace quantities of tiglylglycine were present in urine, a diagnosis of glutaric acidemia type I was initially suspected due to the presence of glutaric and 3-hydroxyglutaric acids. A diagnosis of beta-ketothiolase deficiency was ultimately made through whole exome sequencing which revealed compound heterozygous variants in ACAT1. Fibroblast studies for beta-ketothiolase enzyme activity were confirmatory. The second patient presented at 6 months of age with ketoacidosis, and was found to have elevations of urinary 2-methyl-3-hydroxybutyric acid, 2-methylacetoacetic acid, and tiglylglycine. Sequencing of ACAT1 demonstrated compound heterozygous presumed causative variants. The patient exhibited choreoathethosis 2 months after the acute metabolic decompensation. These cases highlight that, similar to a number of other organic acidemias and mitochondrial disorders, beta-ketothiolase deficiency can present with metabolic stroke. They also illustrate the variability in clinical presentation, imaging, and biochemical evaluation that make screening for and diagnosis of this rare disorder challenging, and further demonstrate the value of whole exome sequencing in the diagnosis of metabolic disorders.

Mitochondrial acetoacetyl-CoA thiolase deficiency: basal ganglia impairment may occur independently of ketoacidosis

BACKGROUND

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency affects ketone body and isoleucine catabolism. Neurological impairment may occur secondary to ketoacidotic episodes. However, we observed neuromotor abnormalities without ketoacidotic events in two T2-deficient families. We hypothesized that the neurological signs were related to the genetic defect and may occur independently of ketoacidotic episodes. We therefore conducted a retrospective review on a French T2-deficient patient series searching for neuromotor impairment.

METHODS

In total, 26 cases were retrospectively analysed for clinical, biological and neuroimaging data.

RESULTS

Neurological findings were observed for 6/26 (23%) patients. Among these, two had never experienced ketoacidotic episodes, though they developed extrapyramidal signs with putamen involvement. Two of the other four patients developed neurological abnormalities before the first ketoacidotic crisis, with putamen involvement in one case. The third patient developed extrapyramidal symptoms more than 10 years after the initial decompensation with globus pallidus involvement. The last patient developed extrapyramidal signs immediately after a severe ketoacidotic crisis with putaminal lesions.

CONCLUSIONS

Most T2-deficient patients achieved normal neurodevelopment. However, on account of the role of T2 in isoleucine catabolism, these patients are potentially exposed to accumulation of toxic isoleucine-derived metabolites, which may contribute to neurological impairment. Our findings confirm previous observations that neurological symptoms in T2 deficiency may occur unrelated to ketoacidosis. The role of protein restriction as a preventive measure against neurological symptoms could not be established in this study and deserves further evaluation. Long-term follow-up data on children diagnosed by newborn screening may clarify the pathogenesis of this neurometabolic association.