A cognitively normal PDH-deficient 18-year-old man carrying the R263G mutation in the PDHA1 gene

Nutritional Interventions for Patients with Mitochondrial POLG-Related Diseases: A Systematic Review on Efficacy and Safety

Ketogenic diet is recommended as a treatment to reduce seizure frequency in patients with intractable epilepsy. The evidence and safety results are sparse for diet interventions in patients with pathogenic polymerase gamma (POLG) variants and intractable epilepsy. The aim of this systematic review is to summarize the efficacy of diet treatment on seizure frequency, clinical symptoms, and potential deleterious effect of liver involvement in patients with mitochondrial diseases caused by pathogenic POLG variants. Literature was searched in PubMed, Embase; and Cochrane in April 2022; no filter restrictions were imposed. The reference lists of retrieved studies were checked for additional literature. Eligibility criteria included verified pathogenic POLG variant and diet treatment. Overall, 880 studies were identified, providing eight case-reports representing nine patients eligible for inclusion. In eight of nine cases, clinical symptoms were improved; six out of nine cases reported improvements in seizure frequency. However, increasing levels of liver enzymes after initiating ketogenic diet were found in four of the nine cases, with one case revealing decreased levels of liver enzymes after initiating long-chain triglyceride restriction. Viewed together, the studies imply that ketogenic diet can have a positive impact on seizure frequency, but may induce progression of liver impairment in patients with pathogenic POLG variants.

Clinical manifestations in two patients with pyruvate dehydrogenase deficiency and long-term survival

Pyruvate dehydrogenase E1-alpha deficiency (PDHAD) results in lactic acidosis and hyperpyruvatemia. Two patients with PDHAD, a man with a p.R263Q mutation, and a girl with a p.C145del mutation in PDHE1α, presented with lactic acidosis with neurological disorder. These patients were able to survive for a long period under careful nursing care. Herein, we discuss the factors contributing to their relatively stable clinical course, albeit with intellectual disability.

Difficulties in recognition of pyruvate dehydrogenase complex deficiency on the basis of clinical and biochemical features. The role of next-generation sequencing

Pyruvate dehydrogenase complex (PDHc) defect is a well-known cause of mitochondrial disorders (MD) with at least six responsible genes (PDHA1, PDHB, DLAT, DLD, PDHX, PDP1). The aim of this work was to assess the diagnostic value of biochemical methods in recognition of PDHc defect in Polish patients with suspicion of MD.

In the first step, Western blot of the E1α subunit was performed on 86 archive muscle bioptates with suspicion of MD. In the second step, Sanger PDHA1 sequencing was performed in 21 cases with low E1α expression. In the third step, 7 patients with negative results of PDHA1 sequencing were subjected to whole-exome sequencing (WES). This protocol revealed 4 patients with PDHA1 and one with DLD mutations. Four additional probands were diagnosed outside the protocol (WES or Sanger sequencing).

The molecular characterization of PDHc defect was conducted in a total of 9 probands: 5 according to and 4 off the protocol. Additionally, two affected relatives were recognized by a family study. Altogether we identified seven different PDHA1 changes, including two novel variants [c.464T > C (p.Met155Thr) and c.856_859dupACTT (p.Arg288Leufs*10)] and one DLD variant.

The lactate response to glucose load in the PDHA1 subset was compared to a subset of non PDHc-related MD. Opposite responses were observed, with an increase of 23% and decrease of 27%, respectively.

The results show that determining lactate response to glucose load and muscle E1α expression may contribute to distinguishing PDHc-related and other MD, however, WES is becoming the method of choice for MD diagnostics.

Defects of thiamine transport and metabolism

Thiamine, in the form of thiamine pyrophosphate, is a cofactor for a number of enzymes which play important roles in energy metabolism. Although dietary thiamine deficiency states have long been recognised, it is only relatively recently that inherited defects in thiamine uptake, activation and the attachment of the active cofactor to target enzymes have been described, and the underlying genetic defects identified. Thiamine is transported into cells by two carriers, THTR1 and THTR2, and deficiency of these results in thiamine-responsive megaloblastic anaemia and biotin-responsive basal ganglia disease respectively. Defective synthesis of thiamine pyrophosphate has been found in a small number of patients with episodic ataxia, delayed development and dystonia, while impaired transport of thiamine pyrophosphate into the mitochondrion is associated with Amish lethal microcephaly in most cases. In addition to defects in thiamine uptake and metabolism, patients with pyruvate dehydrogenase deficiency and maple syrup urine disease have been described who have a significant clinical and/or biochemical response to thiamine supplementation. In these patients, an intrinsic structural defect in the target enzymes reduces binding of the cofactor and this can be overcome at high concentrations. In most cases, the clinical and biochemical abnormalities in these conditions are relatively non-specific, and the range of recognised presentations is increasing rapidly at present as new patients are identified, often by genome sequencing. These conditions highlight the value of a trial of thiamine supplementation in patients whose clinical presentation falls within the spectrum of documented cases.

Thiamine-Responsive and Non-responsive Patients with PDHC-E1 Deficiency: A Retrospective Assessment

Pyruvate dehydrogenase complex (PDHC) deficiency is a disorder of energy metabolism that leads to a range of clinical manifestations. We sought to characterise clinical manifestations and biochemical, neuroimaging and molecular findings in thiamine-responsive and nonresponsive PDHC-deficient patients and to identify potential pitfalls in the diagnosis of PDHC deficiency. We retrospectively reviewed all medical records of all PDHC-deficient patients (n = 19; all had PDHA1 gene mutations) and one patient with severe PDHC deficiency secondary to 3-hydroxyisobutyryl-CoA hydrolase deficiency managed at our centre between 1982 and 2012. Responsiveness to thiamine was based on clinical parameters. Seventeen patients received thiamine treatment: eight did not respond, four showed sustained response and the others responded temporarily/questionably. Sustained response was noted at thiamine doses >400 mg/day. Age at presentation was 0-6 and 12-27 months in the nonresponsive (n = 8) and responsive (n = 4) patients, respectively. Corpus callosum abnormalities were noted in 4/8 nonresponsive patients. Basal ganglia involvement (consistent with Leigh disease) was found in four patients (including 2/4 thiamine-responsive patients). Diagnosis through mutation analysis was more sensitive and specific than through enzymatic analysis. We conclude that patients presenting at age >12 months with relapsing ataxia and possibly Leigh syndrome are more likely to be thiamine responsive than those presenting with neonatal lactic acidosis and corpus callosum abnormalities. However, this distinction is equivocal and treatment with thiamine (>400 mg/day) should be commenced on all patients suspected of having PDHC deficiency. Mutation analysis is the preferable first-line diagnostic test to avoid missing thiamine-responsive patients and misdiagnosing patients with secondary PDHC deficiency.

SHORT SUMMARY

Thiamine responsiveness is more likely in patients presenting at age >12 months with relapsing ataxia and possibly Leigh syndrome than in those presenting with neonatal lactic acidosis and corpus callosum abnormalities. Thiamine doses >400 mg/day are required for sustained response. Mutation analysis is more sensitive and specific than enzymatic analysis as a first-line diagnostic test.

Spectrum of neurological and survival outcomes in pyruvate dehydrogenase complex (PDC) deficiency: lack of correlation with genotype

Pyruvate dehydrogenase complex (PDC) deficiency is a relatively common mitochondrial disorder that primarily presents with neurological manifestations and lactic acidemia. We analyzed the clinical outcomes and neurological features of 59 consented symptomatic subjects (27 M, 32 F), who were confirmed to have PDC deficiency with defined mutations in one of the genes of PDC (PDHA1, n = 53; PDHB, n = 4; DLAT, n = 2), including 47 different mutations, of which 22 were novel, and for whom clinical records and/or structured interviews were obtained. 39% of these subjects (23/59) have died. Of these, 91% (21/23) died before age 4 years, 61% (14/23) before 1 year, and 43% (10/23) before 3 months. 56% of males died compared with 25% of females. Causes of death included severe lactic acidosis, respiratory failure, and infection. In subjects surviving past 6 months, a broad range of intellectual outcomes was observed. Of 42 subjects whose intellectual abilities were professionally evaluated, 19% had normal or borderline intellectual ability (CQ/IQ ≥ 70), 10% had mild intellectual disability (ID) (CQ/IQ 55-69), 17% had moderate ID (CQ/IQ 40-54), 24% had severe ID (CQ/IQ 25-39) and 33% had profound ID (CQ/IQ<25). Assessment by parents was comparable. Of 10 subjects who reached age 12 years, 9 had had professional IQ assessments, and only 4 had IQs ≥ 70 (only 2 of these 4 had assessments after age 12 years). The average outcome for females was severe-to-profound ID, whereas that of males was mild-to-moderate ID. Of subjects for whom specific neurological data were available, the majority had hypotonia (89%), and hypertonia or mixed hyper-/hypotonia (49%) were common. Seizures (57%), microcephaly (49%), and structural brain abnormalities including ventriculomegaly (67%) and agenesis, dysgenesis, or hypoplasia of the corpus callosum (55%) were common. Leigh syndrome was found in only 35%. Structural brain abnormalities were more common in females, and Leigh syndrome was more common in males. In a subgroup of 16 ambulatory subjects >3.5 years in whom balance was evaluated, ataxia was found in 13. Peripheral neuropathy was documented in 2 cases but not objectively evaluated in most subjects. Outcomes of this population with genetically confirmed PDC deficiency are heterogeneous and not distinctive. Correlations between specific genotypes and outcomes were not established. Although more females survive, related to the prevalence of X-linked PDHA1 mutations, symptomatic surviving females are generally more severely impaired cognitively and have a different pattern of neurological impairment compared to males. Neonatal or infant onset of symptoms was associated with poor outcomes. Males with PDHA1 mutations and low fibroblast PDC activity were less likely to survive beyond infancy. Recurrence rate in siblings of subjects with PDHA1 mutation was less than 5%. Paradoxically, in this retrospective review, potential factors considered possibly relevant to development, such as in vitro PDC activity, specific mutations, use of ketogenic diets, supplements, or medications, were generally not confirmed to be significantly correlated with objective outcomes of survival or neuro-cognitive function. Therefore, the basis of variability of these outcomes remains largely undetermined.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤ 20.

The spectrum of pyruvate dehydrogenase complex deficiency: clinical, biochemical and genetic features in 371 patients

CONTEXT

Pyruvate dehydrogenase complex (PDC) deficiency is a genetic mitochondrial disorder commonly associated with lactic acidosis, progressive neurological and neuromuscular degeneration and, usually, death during childhood. There has been no recent comprehensive analysis of the natural history and clinical course of this disease.

OBJECTIVE

We reviewed 371 cases of PDC deficiency, published between 1970 and 2010, that involved defects in subunits E1α and E1β and components E1, E2, E3 and the E3 binding protein of the complex.

DATA SOURCES AND EXTRACTION

English language peer-reviewed publications were identified, primarily by using PubMed and Google Scholar search engines.

RESULTS

Neurodevelopmental delay and hypotonia were the commonest clinical signs of PDC deficiency. Structural brain abnormalities frequently included ventriculomegaly, dysgenesis of the corpus callosum and neuroimaging findings typical of Leigh syndrome. Neither gender nor any clinical or neuroimaging feature differentiated the various biochemical etiologies of the disease. Patients who died were younger, presented clinically earlier and had higher blood lactate levels and lower residual enzyme activities than subjects who were still alive at the time of reporting. Survival bore no relationship to the underlying biochemical or genetic abnormality or to gender.

CONCLUSIONS

Although the clinical spectrum of PDC deficiency is broad, the dominant clinical phenotype includes presentation during the first year of life; neurological and neuromuscular degeneration; structural lesions revealed by neuroimaging; lactic acidosis and a blood lactate:pyruvate ratio ≤20.