Natural history of Leigh disease


Leigh syndrome is a neurodegenerative disease associated with primary or secondary mitochondrial dysfunction at the level of oxidative phosphorylation.

Sofou et al. published a retrospective study describing patients with Leigh syndrome (n=130; 77 with pathogenic mutations) from eight European centers specializing in mitochondrial diseases. They described the natural history of Leigh syndrome and identified novel predictors of disease severity and long-term outcome.

The median age at presentation was 7 months, with 80% of patients presenting below 2 years old. 39% of patients had died by the age of 21 years, at a median age of 2.4 years. Increased CSF lactate was significantly correlated to a more severe disease course, characterized by early onset before 6 months of age, acute exacerbations and/or relapses, as well as brainstem involvement. Disease onset before 6 months of age, failure to thrive, brainstem lesions on neuroimaging and intensive care treatment were significantly associated with poorer survival.

The most common clinical features at onset were abnormal motor findings in ~80% of cases (e.g. hypotonia, dystonia) and abnormal ocular findings in 25% of patients (e.g. nystagmus, strabismus, visual impairment, optic atrophy, ptosis, ophthalmoplegia).

Clinical features throughout the disease course: more than 50% had at least three affected organ systems (most commonly, motor, visual and gastrointestinal systems). Epileptic seizures were present in 40% of patients, respiratory dysfunction in 38% (e.g. hyperventilation and/or abnormal breathing pattern, apnoea, obstructive or restrictive respiratory disease, central hypoventilation), and cardiac dysfunction in 18% (e.g. hypertrophic cardiomyopathy > arrhythmia/conduction defects > dilated cardiomyopathy).

A multicenter study on Leigh syndrome: disease course and predictors of survival. Sofou K, De Coo IF, Isohanni P, Ostergaard E, Naess K, De Meirleir L, Tzoulis C, Uusimaa J, De Angst IB, Lönnqvist T, Pihko H, Mankinen K, Bindoff LA, Tulinius M, Darin N. Orphanet J Rare Dis. 2014 Apr 15;9:52. doi: 10.1186/1750-1172-9-52. PMID: 24731534

Posted by Yannis Trakadis, MD


Combined cysteamine bitartrate and N-acetylcysteine for NCL

Posted by & filed under Part 16: LYSOSOMAL DISORDERS, Treatment.

Levin et al (2014) recently reported on a study exploring the impact of combined oral cysteamine bitartrate (60 mg/kg per day) and N-acetylcysteine (60 mg/kg per day) in patients with neuronal ceroid lipofuscinosis (n=10, age range: 6 months to 3 years old).

Assessments took place every 6-12 months until the patients had an isoelectric EEG or were too ill to travel. Electroretinography, brain MRI/MRS, electron microscopic analyses of leukocytes for granular osmiophilic deposits (GRODs), and physical/ neurodevelopmental assessments on the Denver scale were also performed.

Combination therapy with cysteamine bitartrate and N-acetylcysteine was associated with delay of isoelectric EEG (average time to isoelectric EEG was 52 months compared with 36 months in previous publications), depletion of GRODs, and subjective benefits as reported by parents and physicians (less irritability, improved alertness).

Oral cysteamine bitartrate and N-acetylcysteine for patients with infantile neuronal ceroid lipofuscinosis: a pilot study. Levin SW, Baker EH, Zein WM, Zhang Z, Quezado ZM, Miao N, Gropman A, Griffin KJ, Bianconi S, Chandra G, Khan OI, Caruso RC, Liu A, Mukherjee AB. Lancet Neurol. 2014 Aug;13(8):777-87. PMID: 24997880

posted by Yannis Trakadis, MD

Genome-wide association study of MMR-related febrile seizures

Posted by & filed under Part 28: NEUROGENETICS.

Feenstra B et al. Common variants associated with general and MMR vaccine-related febrile seizures. Nat Genet. 2014 Dec;46(12):1274-82. Epub 2014 Oct 26.

Febrile seizures are a well-known side-effect of MMR (measles-mumps-rubella) vaccination. Polymorphisms associated with an increased risk of febrile seizures in general have been identified previously (particularly in genes encoding ion channels); this study addresses the question of whether distinct variants influence the risk of febrile seizures specifically as a reaction to MMR vaccination. The authors performed a series of genome-wide association scans comparing children with MMR-related febrile seizures, children with febrile seizures unrelated to vaccination, and healthy controls.

Polymorphisms in two genes were associated distinctly with MMR-associated seizures: the interferon-stimulated gene IFI44L, and CD46, encoding the measles virus receptor. Four loci were associated with febrile seizures in general, implicating: two sodium channel genes (SCN1A and SCN2A), a region associated with magnesium levels, and ANO3, a TMEM16 family gene. To explore the functional significance of the latter gene, the authors performed electrophysiological recording in brain slices from wild-type and Ano3-null rats, and found that in the latter hypothalamic neurons were less responsive to heat, whereas hippocampal neurons became hyperexcitable with rises in temperature.

This study suggests that MMR-associated febrile seizures involve an interplay between neurological and immunological genetic risk factors, and opens a promising avenue for further study.


Folinic acid in the treatment of schizophrenia associated with folate receptor antibodies

Posted by & filed under Part 17: VITAMINS.

Ramaekers VT et al. Folinic acid treatment for schizophrenia associated with folate receptor autoantibodies. Mol Genet Metab. 2014 Dec;113(4):307-14.


This study suggests an exciting avenue for treatment and scientific inquiry  in schizophrenia.

Previous reports have associated schizophrenia with perturbed folate metabolism, and cerebral folate deficiency due to serum antibodies against folate receptor alpha (which transfers methyltetrahydrofolate to the brain at the choroid plexus) has been reported in a patient with catatonic schizophrenia whose auditory hallucinations disappeared with folinic acid treatment. In this study, Ramaekers et al. first identified a 17-year-old girl diagnosed with refractory paranoid schizophrenia and multiple suicide attempts who was found to have low CSF MTHF levels associated with blocking antibodies against folate receptor alpha (FRa); folinic acid treatment resulted in a full recovery. They then recruited seventeen more patients with refractory schizophrenia, and screened them for blocking FRa antibodies and for evidence of cerebral folate deficiency. Surprisingly, they found that that 15/18 patients (83.3%) had positive FRa antibody titres, as opposed to 3.3% of controls, though levels fluctuated dramatically. Seven of these patients consented to a trial of folinic acid treatment and showed significant clinical improvement. The study also found a positive linear correlation between CSF MTHF and biopterin levels.

Further study is, of course, needed to confirm that cerebral folate deficiency due to FRa antibodies is a significant contributing factor to schizophrenia. In the current study, the number of patients was very small, and the trial of treatment with folinic acid was uncontrolled and non-blinded. Also, the inclusion of the initial patient, whose dramatic response prompted the study, into the study data, may have introduced a bias. Nevertheless, even if larger studies show the findings not to be easily generalisable, the fact that some patients do respond dramatically to treatment suggests that it may be worthwhile to screen for FRa antibodies and/or folinic acid responsiveness in patients with refractory schizophrenia.

This article makes for very enjoyable reading, as it includes a clear and concise review of the more recent NMDA glutamate receptor hypofunction hypothesis of schizophrenia, as well as of cerebral folate metabolism. The authors also propose an elegant hypothesis to connect the alternating positive and negative symptoms of schizophrenia with fluctuating titres of FRa antibodies.

The gut microbiota influence blood brain barrier integrity

Posted by & filed under Part 03: GENERAL THEMES.

Braniste et al. recently reported in Science Translational Medicine (2014 Nov 19;6(263):263ra158. doi: 10.1126/scitranslmed.3009759) that the permeability of the mouse blood brain barrier (BBB) is influenced by the gut microbiome. They showed that germ-free mice, beginning in intrauterine life, displayed increased BBB permeability compared to mice of the same strain with normal gut flora. The increased BBB permeability was associated with reduced expression of specific tight junction proteins that regulate barrier function. Expression of these same  proteins could be upregulated by exposure of germ-free mice to gut microbiota.


Hilary Vernon, MD PhD

Thiamine pyrophosphokinase deficiency: a treatable inborn error of metabolism

Posted by & filed under Part 17: VITAMINS.

Banka S et al. Expanding the clinical and molecular spectrum of thiamine pyrophosphokinase deficiency: A treatable neurological disorder caused by TPK1 mutations. Mol Genet Metab. 2014 Oct 5. [Epub ahead of print]


Thiamine pyrophosphokinase (TPK) deficiency causing episodic encephalopathy type thiamine metabolism dysfunction is the most recently discovered thiamine-responsive inborn error of metabolism, with only five patients previously described in the literature. Lactic acidosis and 2-ketoglutaric aciduria appear to be markers of this disorder, although they do not seem to have been present in all cases. Banka et al describe two new patients with TPK deficiency, of which one had a non-episodic Leigh syndrome-like neurological presentation, thus expanding the clinical spectrum of this disorder. Significantly, an attempt to introduce a ketogenic diet in this patient before the diagnosis was made (and therefore before thiamine supplementation was introduced) resulted in severe metabolic acidosis and irreversible neurodevelopmental regression. The authors also describe assays for TPK enzyme activity measurement and thiamine pyrophosphate quantification in frozen muscle and blood.

This study highlights the importance of considering this potentially treatable disorder in the differential diagnosis of episodic encephalopathy or non-episodic Leigh-like syndrome, particularly in the presence of 2-ketoglutaric aciduria. It should also be considered before a ketogenic diet is offered to a patient in the absence of a firm alternative diagnosis.


Towards chaperone therapy in pyridoxine-resistant classical homocystinuria

Posted by & filed under Part 08: AMINO ACIDS.

Melenovská P, Kopecká J, Krijt J, Hnízda A, Raková K, Janošík M, Wilcken B, Kožich V.  Chaperone therapy for homocystinuria: the rescue of CBS mutations by heme arginate. J Inherit Metab Dis. 2014 Oct 21. [Epub ahead of print]


Mutations in the CBS gene cause classical homocystinuria (cystathionine beta-synthase deficiency). For patients who do not respond to pyridoxine, CBS deficiency requires pharmacological treatment with betaine and folates, as well as highly demanding nutritional management. Previous research has shown that many of the pathogenic mutations in CBS cause protein misfolding, and that correct folding of the enzyme requires the co-translational presence of heme or related metalloporphyrins.

Melenovská et al test three compounds with chaperone-like activity, and describe the rescue of some CBS mutations by heme arginate in mammalian cells and human fibroblasts. Interestingly, while some of the heme-responsive mutations are thought to disrupt the heme-binding pocket of the enzyme, others are located distally to it; the authors postulate that, for these mutants, oversaturation with heme may induce favourable allosteric changes.

Unfortunately, as the authors note, the direct clinical applications of these findings are limited, as heme arginate requires intravenous administration and carries a significant risk of toxicity. On the other hand, these findings do point to the heme-binding pocket of the CBS enzyme as a promising target for chaperone therapy.


Cornelia de Lange Syndrome and HDAC8 mutations

Posted by & filed under New IEM.

I recently saw a female patient with a clinically apparent genetic mosaic abnormality, including patchy distribution of hyperpigmentation, organ hemi-hypertrophy, and dental and skeletal abnormalities. Testing for obvious genetic causes including CDPX and Incontinentia Pigmenti were non-informative.  We sent whole exome sequencing which revealed a novel, presumed loss of function mutation in HDAC8.

Loss-of-function mutations in HDAC8 were recently associated with X-linked Cornelia de Lange syndrome (Kaiser et al, Hum Mol Genet. 2014 Jun 1;23(11):2888-900. doi: 10.1093/hmg/ddu002). This is a diagnosis we would have never otherwise considered in this patient, and caused us to reason that mutations in HDAC8 should be considered in girls with a CDPX or IP like clinical presentation in whom genetic testing has been uninformative.

Hilary Vernon, MD PhD

Antisense therapy in Galactosemia

Posted by & filed under Part 07: CARBOHYDRATES, Treatment.

Mutational analysis of patients with galactosemia Portugal revealed the intronic variation c.820+13A>G as the second most prevalent mutation. Coelho et al. functionally characterized this intronic variation and studied its pathogenic mechanism.

Minigene splicing assays in two distinct cell lines and patients’ transcript analyses showed that the mutation activates a cryptic donor splice site, inducing an aberrant splicing of the GALT pre-mRNA, which in turn leads to a frameshift with inclusion of a premature stop codon (p.D274Gfs*17). Functional-structural studies showed that the truncated GALT lacks enzymatic activity and is prone to aggregation.

Antisense therapy was then used to correct this intronic mutation activating cryptic splice sites and successfully restored the constitutive splicing. Given the current diet-based treatment for classic galactosemia remains insufficient, antisense therapy as an alternative treatment strategy may be interesting to explore further.

Functional correction by antisense therapy of a splicing mutation in the GALT gene. Coelho et al. Eur J Hum Genet. 2014 Jul 23. PMID: 25052314

Posted by Yannis Trakadis, MD

zebrafish as a model for IEM research

Posted by & filed under _.

Wager et al. provide an interesting overview of how zebrafish can be used as a model for inborn errors of metabolism to understand their mechanistic basis. Available methods for creating and studying zebrafish disease models, advantages and disadvantages of using this model organism, novel mechanistic insights already provided using this model, and successful examples of its use for drug discovery and development are reviewed.

Modelling inborn errors of metabolism in zebrafish. Wager K, Mahmood F, Russell C. J Inherit Metab Dis. 2014 Jul;37(4):483-95. PMID: 24797558

Posted by Yannis Trakadis, MD