Thiamine Pyrophosphokinase Deficiency due to Mutations in the TPK1 Gene: A Rare, Treatable Neurodegenerative Disorder

Biochemical and medical aspects of vitamin B1 research

Vitamin B1 is an indispensable food factor for the human and animal body. In animals, vitamin B1 is found in the form of thiamine and its phosphate esters - thiamine mono-, di- and triphosphate, as well as an adenylated derivative - adenosine thiamine triphosphate. At present, the only vitamin B1 form with biochemical functions being elucidated is thiamine diphosphate, which serves as a coenzyme for several important enzymes involved in carbohydrate, amino acid, fatty acid and energy metabolism. Here we review the latest developments in the field of vitamin B1 research in animals. Transport, metabolism and biological role of thiamine and its derivatives are considered as well as the involvement of vitamin B1-dependent processes in human diseases and its therapeutic issues, a field that has gained momentum with several important recent developments.

Clinical and biochemical footprints of inherited metabolic diseases: Ia. Movement disorders, updated

Movement disorders are a common manifestation of inherited metabolic diseases (IMDs), categorized into hyperkinetic movement disorders, hypokinetic-rigid syndromes, ataxia, and spasticity. We reviewed and updated the list of known metabolic disorders associated with movement disorders, identifying a total of 559 IMDs. We outlined the more common and treatable causes, sorted by the dominant movement disorder phenomenology, and provided a practical clinical approach for suspected IMDs presenting with movement disorders. This work represents an updated catalog in a series of articles aimed at creating and maintaining a comprehensive list of clinical and metabolic differential diagnoses based on system involvement.

The wide phenotypic spectrum of thiamine metabolism dysfunction syndrome 5 and its treatment

Thiamine metabolism dysfunction syndrome 5 (TMDS5) is a rare inborn error of metabolism caused by variants in TPK1, leading to reduced TPK levels. This enzyme is crucial for the production of thiamine pyrophosphate, the active form of thiamine, a vital coenzyme in numerous metabolic pathways. The clinical presentation exhibits a diverse range of manifestations. In this review, we explore reported cases in the literature and present two cases representing the extremes of the clinical spectrum: recurrent ataxia and Leigh syndrome. The former phenotype follows a milder course. The second one is characterized by early onset and severe symptoms, including dystonia, epilepsy, and developmental regression, progressing rapidly to severe disability with high mortality. Typically, children exposed to infectious or traumatic triggers display episodes marked by ataxia and dystonia, with periods of good health or only mild disabilities in between. Treatment with the phosphorylated thiamine active bioform, TPP, is more effective in the recurrent ataxia form, especially when initiated promptly at symptom onset. Further studies are needed to identify available biomarkers and establish correlations between different variants, severity, and treatment response.

Mitochondrial disorder diagnosis and management- what the pediatric neurologist wants to know

Childhood-onset mitochondrial disorders are rare genetic diseases that often manifest with neurological impairment due to altered mitochondrial structure or function. To date, pathogenic variants in 373 genes across the nuclear and mitochondrial genomes have been linked to mitochondrial disease, but the ensuing genetic and clinical complexity of these disorders poses considerable challenges to their diagnosis and management. Nevertheless, despite the current lack of curative treatment, recent advances in next generation sequencing and -omics technologies have laid the foundation for precision mitochondrial medicine through enhanced diagnostic accuracy and greater insight into pathomechanisms. This holds promise for the development of targeted treatments in this group of patients. Against a backdrop of inherent challenges and recent technological advances in mitochondrial medicine, this review discusses the current diagnostic approach to a child with suspected mitochondrial disease and outlines management considerations of particular relevance to paediatric neurologists. We highlight the importance of mitochondrial expertise centres in providing the laboratory infrastructure needed to supplement uninformative first line genomic testing with focused and/or further unbiased investigations where needed, as well as coordinating an integrated multidisciplinary model of care that is paramount to the management of patients affected by these conditions.

Report of a novel recurrent homozygous variant c.620A>T in three unrelated families with thiamine metabolism dysfunction syndrome 5 and review of literature

INTRODUCTION

Biallelic variants in thiamine pyrophosphokinase 1 ( TPK1 ) are known to cause thiamine metabolism dysfunction syndrome 5 (THMD5). This disorder is characterized by neuroregression, ataxia and dystonia with basal ganglia abnormalities on neuroimaging. To date, 27 families have been reported with THMD5 due to variants in TPK1 .

METHODS

We ascertained three individuals from three unrelated families. Singleton exome sequencing was performed on all three individuals, followed by in silico mutagenesis of the mutant TPK protein. Additionally, we reviewed the genotypic and phenotypic information of 27 previously reported individuals with THMD5.

RESULTS

Singleton exome sequencing revealed a novel homozygous variant c.620A>T p.(Asp207Val) in TPK1 (NM_022445.4) in all three individuals. In silico mutagenesis of the mutant protein revealed a decrease in protein stability and altered interactions with its neighboring residues compared to the wild-type protein. Thus, based on strikingly similar clinical and radiological findings compared to the previously reported individuals and with the support of in silico mutagenesis findings, the above-mentioned variant appears to be the probable cause for the condition observed in the affected individuals in this study.

CONCLUSION

We report a novel homozygous variant in TPK1 , which appears to be recurrent among the Indian population.

Thiamine pyrophosphokinase deficiency: report of two Chinese cases and a literature review

Thiamine pyrophosphokinase (TPK) deficiency, is a rare autosomal recessive disorder of congenital metabolic dysfunction caused by variants in the TPK1 gene. TPK1 variants can lead to thiamine metabolic pathway obstacles, and its clinical manifestations are highly variable. We describe two cases of TPK deficiency with completely different phenotypes and different therapeutic effects, and 26 cases of previously reported were retrospectively reviewed to improve our understanding of the clinical and genetic features of the disease. Patients with TPK deficiency present with ataxia, dysarthria, dystonia, disturbance of consciousness, seizures, and other nervous system dysfunction. Different gene variant sites may lead to different clinical features and therapeutic effects. Gene analysis is important for the diagnosis of TPK deficiency caused by TPK1 variants, and thiamine supplementation has been the mainstay of treatment for TPK deficiency to date.

The Therapeutic Potential of Vitamins B1, B3 and B6 in Charcot-Marie-Tooth Disease with the Compromised Status of Vitamin-Dependent Processes

Understanding the molecular mechanisms of neurological disorders is necessary for the development of personalized medicine. When the diagnosis considers not only the disease symptoms, but also their molecular basis, treatments tailored to individual patients may be suggested. Vitamin-responsive neurological disorders are induced by deficiencies in vitamin-dependent processes. These deficiencies may occur due to genetic impairments of proteins whose functions are involved with the vitamins. This review considers the enzymes encoded by the DHTKD1, PDK3 and PDXK genes, whose mutations are observed in patients with Charcot-Marie-Tooth (CMT) disease. The enzymes bind or produce the coenzyme forms of vitamins B1 (thiamine diphosphate, ThDP) and B6 (pyridoxal-5'-phosphate, PLP). Alleviation of such disorders through administration of the lacking vitamin or its derivative calls for a better introduction of mechanistic knowledge to medical diagnostics and therapies. Recent data on lower levels of the vitamin B3 derivative, NAD+, in the blood of patients with CMT disease vs. control subjects are also considered in view of the NAD-dependent mechanisms of pathological axonal degeneration, suggesting the therapeutic potential of vitamin B3 in these patients. Thus, improved diagnostics of the underlying causes of CMT disease may allow patients with vitamin-responsive disease forms to benefit from the administration of the vitamins B1, B3, B6, their natural derivatives, or their pharmacological forms.

Case report of two affected siblings in a family with thiamine metabolism dysfunction syndrome 5: a rare, but treatable neurodegenerative disease

Background

Thiamine metabolism dysfunction syndrome 5 (THMD5) is a rare inherited metabolic disorder due to thiamine pyrophosphokinase 1(TPK1) deficiency, caused by mutations in TPK1. The core symptoms of the disease is acute or subacute onset encephalopathy, ataxia, muscle hypotonia, and regression of developmental milestones in early infancy, repeatedly triggered by acute infectious illness. However, we report two brothers of THMD5 with compound heterozygous for the mutations c.614-1G > A,c.224 T > A p.(Ile75Asn), but the prognosis is quite different if thiamine suppled. According to our current knowledge, the missense variant c.224 T > A p.(Ile75Asn) was not published previously.

Case presentation

Here, we describe two affected siblings in a Chinese family, after an uneventful pregnancy to non-consanguineous and healthy parents. The older brother presented with normal development during the first 6 months of life, but developed regression of developmental milestones after, accompanied with muscle hypotonia, and chronic encephalopathy, and died at 1 year and 6 months old. The younger brother presented with acute onset encephalopathy, ataxia, muscle hypotonia, repeatedly triggered by acute infectious illness. He was compound heterozygous for the mutations c.614-1G > A,c.224 T > A p.(Ile75Asn) identified by whole exome sequencing. He was diagnosed of THMD5 when he was 11 month. Oral supplementation of thiamine 100 mg/day, the symptoms gradually disappeared. At the age of 2 years and 4 months, he stoped thiamine, his symptoms returned and were once again relieved by oral supplementation of thiamine 100 mg/day.

Conclusions

THMD5 is a rare, but treatable neurodegenerative disease, the clinical phenotype ranges from mild to severe. Massive-dose of thiamine supplementation may ameliorate the course of TPK1 deficiency. When similar clinical cases appear, gene detection is particularly important, which is conducive to early diagnosis. Treatment with thiamine while awaiting the outcome of diagnostic tests may be a good choice.

Product inhibition of mammalian thiamine pyrophosphokinase is an important mechanism for maintaining thiamine diphosphate homeostasis

BACKGROUND

Thiamine diphosphate (ThDP), an indispensable cofactor for oxidative energy metabolism, is synthesized through the reaction thiamine + ATP ⇆ ThDP + AMP, catalyzed by thiamine pyrophosphokinase 1 (TPK1), a cytosolic dimeric enzyme. It was claimed that the equilibrium of the reaction is in favor of the formation of thiamine and ATP, at odds with thermodynamic calculations. Here we show that this discrepancy is due to feedback inhibition by the product ThDP.

METHODS

We used a purified recombinant mouse TPK1 to study reaction kinetics in the forward (physiological) and for the first time also in the reverse direction.

RESULTS

Keq values reported previously are strongly underestimated, due to the fact the reaction in the forward direction rapidly slows down and reaches a pseudo-equilibrium as ThDP accumulates. We found that ThDP is a potent non-competitive inhibitor (Ki ≈ 0.4 μM) of the forward reaction. In the reverse direction, a true equilibrium is reached with a Keq of about 2 × 10-5, strongly in favor of ThDP formation. In the reverse direction, we found a very low Km for ThDP (0.05 μM), in agreement with a tight binding of ThDP to the enzyme.

GENERAL SIGNIFICANCE

Inhibition of TPK1 by ThDP explains why intracellular ThDP levels remain low after administration of even very high doses of thiamine. Understanding the consequences of this feedback inhibition is essential for developing reliable methods for measuring TPK activity in tissue extracts and for optimizing the therapeutic use of thiamine and its prodrugs with higher bioavailability under pathological conditions.

Treatable Hyperkinetic Movement Disorders Not to Be Missed

Hyperkinetic movement disorders are characterized by the presence of abnormal involuntary movements, comprising most notably dystonia, chorea, myoclonus, and tremor. Possible causes are numerous, including autoimmune disorders, infections of the central nervous system, metabolic disturbances, genetic diseases, drug-related causes and functional disorders, making the diagnostic process difficult for clinicians. Some diagnoses may be delayed without serious consequences, but diagnosis delays may prove detrimental in treatable disorders, ranging from functional disabilities, as in dopa-responsive dystonia, to death, as in Whipple's disease. In this review, we focus on treatable disorders that may present with prominent hyperkinetic movement disorders.