Bi-allelic variants in CHKA cause a neurodevelopmental disorder with epilepsy and microcephaly.

The Kennedy pathways catalyse the de novo synthesis of phosphatidylcholine and phosphatidylethanolamine, the most abundant components of eukaryotic cell membranes. In recent years, these pathways have moved into clinical focus because four of ten genes involved have been associated with a range of autosomal recessive rare diseases such as a neurodevelopmental disorder with muscular dystrophy (CHKB), bone abnormalities and cone-rod dystrophy (PCYT1A) and spastic paraplegia (PCYT2, SELENOI). We identified six individuals from five families with bi-allelic variants in CHKA presenting with severe global developmental delay, epilepsy, movement disorders and microcephaly. Using structural molecular modelling and functional testing of the variants in a cell-based Saccharomyces cerevisiae model, we determined that these variants reduce the enzymatic activity of CHKA and confer a significant impairment of the first enzymatic step of the Kennedy pathway. In summary, we present CHKA as a novel autosomal recessive gene for a neurodevelopmental disorder with epilepsy and microcephaly.

Normal Thermostability of p.Ser113Leu and p.Arg631Cys Variants of Mitochondrial Carnitine Palmitoyltransferase II (CPT II) in Human Muscle Homogenate.

Previous fibroblast and recombinant enzyme studies showed a markedly thermolabile p.Ser113Leu variant compared to the wild-type (WT) in muscle carnitine palmitoyltransferase II (CPT II) deficiency. Additionally, it has been shown that cardiolipin (CLP) stimulated or inhibited the p.Ser113Leu recombinant variant depending on the pre-incubation temperatures. In this study, the thermolabilities of mitochondrial enzyme CPT II in muscle homogenates of patients with the p.Ser113Leu (n = 3) and p.Arg631Cys (n = 2) variants were identified to be similar to that of WT. Pre-incubation with CLP on ice stimulated the WT enzyme more than both variants. However, CLP stimulated the variants and WT at 46 °C to about 6-18-fold. The present data indicate that the thermostability of CPT II variant in muscle homogenate is similar to that of WT. This is in contrast to the increased thermolability of enzymes derived from fibroblast and that of recombinant enzymes. Hence, it can be speculated that the disruption of the compartmentation in muscle homogenate mediates a protective effect on the thermolability of the native variant. However, the exact mechanism remains unclear. However, the activating effect of CLP on CPT II in muscle homogenate seems to align with those on recombinant enzymes.

The Mitochondrial Biomarkers FGF-21 and GDF-15 in Patients with Episodic and Chronic Migraine.

Mitochondrial processes may play a role in the pathophysiology of migraine. Serum levels of two biomarkers, Fibroblast-growth-factor 21 (FGF-21) and Growth-differentiation-factor 15 (GDF-15), are typically elevated in patients with mitochondrial disorders. The study investigated whether the presence of migraine may influence FGF-21 and GDF-15 serum levels considering vascular and metabolic disorders as possible confounders. A cross-sectional study in two headache centers was conducted analyzing GDF-15 and FGF-21 serum concentration in 230 patients with episodic and chronic migraine compared to a control group. Key clinical features of headache were evaluated, as well as health-related life quality, anxiety and depression using SF-12 and HADS-questionnaires. Elevated GDF-15 values were detected in the migraine group compared to the control group (506.65 ± 275.87 pg/mL vs. 403.34 ± 173.29 pg/mL, p < 0.001, Mann-Whitney U test). A strong correlation between increasing age and higher GDF-15 levels was identified (p < 0.001, 95%-CI elevation of GDF-15 per year 5.246-10.850 pg/mL, multiple linear regression). Mean age was different between the groups, and this represents a confounding factor of the measurements. FGF-21 levels did not differ between migraine patients and controls (p = 0.635, Mann-Whitney U test) but were significantly influenced by increasing BMI (p = 0.030, multiple linear regression). Neither biomarker showed correlation with headache frequency. Higher FGF-21 levels were associated with a higher mean intensity of headache attacks, reduced health-related life quality and anxiety. When confounding factors were considered, increased serum levels of FGF-21 and GDF-15 were not detected in migraine patients. However, the results show an age-dependence of GDF-15 in migraine patients, and this should be considered in future studies. Similar findings apply to the relationship between FGF-21 and BMI. Previous studies that did not adjust for these factors should be interpreted with caution.

Heteroplasmy and Copy Number in the Common m.3243A>G Mutation-A Post-Mortem Genotype-Phenotype Analysis.

Different mitochondrial DNA (mtDNA) mutations have been identified to cause mitochondrial encephalopathy, lactate acidosis and stroke-like episodes (MELAS). The underlying genetic cause leading to an enormous clinical heterogeneity associated with m.3243A>G-related mitochondrial diseases is still poorly understood. Genotype-phenotype correlation (heteroplasmy levels and clinical symptoms) was analysed in 16 patients (15 literature cases and one unreported case) harbouring the m.3243A>G mutation. mtDNA copy numbers were correlated to heteroplasmy levels in 30 different post-mortem tissue samples, including 14 brain samples of a 46-year-old female. In the central nervous system, higher levels of heteroplasmy correlated significantly with lower mtDNA copy numbers. Skeletal muscle levels of heteroplasmy correlated significantly with kidney and liver. There was no significant difference of heteroplasmy levels between clinically affected and unaffected patients. In the patient presented, we found >75% heteroplasmy levels in all central nervous system samples, without harbouring a MELAS phenotype. This underlines previous suggestions, that really high levels in tissues do not automatically lead to a specific phenotype. Missing significant differences of heteroplasmy levels between clinically affected and unaffected patients underline recent suggestions that there are additional factors such as mtDNA copy number and nuclear factors that may also influence disease severity.

The m.9143T>C Variant: Recurrent Infections and Immunodeficiency as an Extension of the Phenotypic Spectrum in MT-ATP6 Mutations?

Pathogenic variants in the MT-ATP6 are a well-known cause for maternally inherited mitochondrial disorders associated with a wide range of clinical phenotypes. Here, we present a 31- year old female with insulin-dependent diabetes mellitus, recurrent lactic acidosis and ketoacidosis recurrent infections with suspected immunodeficiency with T cell lymphopenia and hypogammaglobulinemia as well as proximal tetraparesis with severe muscle and limb pain and rapid physical exhaustion. Muscle biopsy and respiratory chain activities were normal. Single-exome sequencing revealed a variant in the MT-ATP6 gene: m.9143T>C. Analysis of further specimen of the index and mother (segregation studies) revealed the highest mutation load in muscle (99% level of mtDNA heteroplasmy) of the index patient. Interestingly, acute metabolic and physical decompensation during recurrent illness was documented to be a common clinical feature in patients with MT-ATP6 variants. However, it was not mentioned as a key symptom. Thus, we suggest that the clinical spectrum might be expanded in ATP6-associated diseases.

FGF-21 as a Potential Biomarker for Mitochondrial Diseases.

The diagnosis of mitochondrial diseases is still challenging due to clinical and genetical heterogeneity. The development of advanced technologies including Whole-Exome- Sequencing (WES) and Whole-Genome-Sequencing (WGS) has led to improvements in genetic diagnosis. However, a reliable biomarker in serum could enhance and ease the diagnosis and indeed reduce the need for muscle biopsy. Several studies suggest Fibroblast growth factor 21 (FGF-21) as a biomarker for diagnosis in mitochondrial disorders. It is known, that in patients with mitochondrial disorders, the expression of FGF-21 gets elevated in an effort to counteract the underlying metabolic deficiency. The growth and differentiation factor 15 (GDF-15) has been described as a potential biomarker for mitochondrial diseases, too. In the present review, a literature research, using PubMed database about the reliability of FGF-21 as a biomarker for mitochondrial disorders and its comparison with GDF-15 has been performed.