1.
Diseases Caused by Mutations in Mitochondrial Carrier Genes SLC25: A Review.
Palmieri, F, Scarcia, P, Monné, M
Biomolecules. 2020;(4)
Abstract
In the 1980s, after the mitochondrial DNA (mtDNA) had been sequenced, several diseases resulting from mtDNA mutations emerged. Later, numerous disorders caused by mutations in the nuclear genes encoding mitochondrial proteins were found. A group of these diseases are due to defects of mitochondrial carriers, a family of proteins named solute carrier family 25 (SLC25), that transport a variety of solutes such as the reagents of ATP synthase (ATP, ADP, and phosphate), tricarboxylic acid cycle intermediates, cofactors, amino acids, and carnitine esters of fatty acids. The disease-causing mutations disclosed in mitochondrial carriers range from point mutations, which are often localized in the substrate translocation pore of the carrier, to large deletions and insertions. The biochemical consequences of deficient transport are the compartmentalized accumulation of the substrates and dysfunctional mitochondrial and cellular metabolism, which frequently develop into various forms of myopathy, encephalopathy, or neuropathy. Examples of diseases, due to mitochondrial carrier mutations are: combined D-2- and L-2-hydroxyglutaric aciduria, carnitine-acylcarnitine carrier deficiency, hyperornithinemia-hyperammonemia-homocitrillinuria (HHH) syndrome, early infantile epileptic encephalopathy type 3, Amish microcephaly, aspartate/glutamate isoform 1 deficiency, congenital sideroblastic anemia, Fontaine progeroid syndrome, and citrullinemia type II. Here, we review all the mitochondrial carrier-related diseases known until now, focusing on the connections between the molecular basis, altered metabolism, and phenotypes of these inherited disorders.
2.
Review of SRD5A3 Disease-Causing Sequence Variants and Ocular Findings in Steroid 5α-Reductase Type 3 Congenital Disorder of Glycosylation, and a Detailed New Case.
Kousal, B, Honzík, T, Hansíková, H, Ondrušková, N, Čechová, A, Tesařová, M, Stránecký, V, Meliška, M, Michaelides, M, Lišková, P
Folia biologica. 2019;(3):134-141
Abstract
Steroid 5α-reductase type 3 congenital disorder of glycosylation (SRD5A3-CDG) is a severe metabolic disease manifesting as muscle hypotonia, developmental delay, cerebellar ataxia and ocular symptoms; typically, nystagmus and optic disc pallor. Recently, early onset retinal dystrophy has been reported as an additional feature. In this study, we summarize ocular phenotypes and SRD5A3 variants reported to be associated with SRD5A3-CDG. We also describe in detail the ophthalmic findings in a 12-year-old Czech child harbouring a novel homozygous variant, c.436G>A, p.(Glu146Lys) in SRD5A3. The patient was reviewed for congenital nystagmus and bilateral optic neuropathy diagnosed at 13 months of age. Examination by spectral domain optical coherence tomography and fundus autofluorescence imaging showed clear signs of retinal dystrophy not recognized until our investigation. Best corrected visual acuity was decreased to 0.15 and 0.16 in the right and left eye, respectively, with a myopic refractive error of -3.0 dioptre sphere (DS) / -2.5 dioptre cylinder (DC) in the right and -3.0 DS / -3.0 DC in the left eye. The proband also had optic head nerve drusen, which have not been previously observed in this syndrome.
3.
Identifying mutations in epilepsy genes: Impact on treatment selection.
Perucca, P, Perucca, E
Epilepsy research. 2019;:18-30
Abstract
The last decade saw impressive advances not only in the discovery of gene mutations causing epilepsy, but also in unraveling the molecular mechanisms underlying the clinical manifestations of the disease. Increasing evidence is emerging that understanding these mechanisms is relevant for selection of the most appropriate treatment in the affected individual(s). The present article discusses the therapeutic implications of epilepsy-causing variants affecting a broad range of targets, from ion channels to genes controlling cellular metabolism and cell signaling pathways. Identification of a precise genetic etiology can direct physicians to (i) prescribe treatments that correct specific metabolic defects (e.g., the ketogenic diet for GLUT1 deficiency, or pyridoxine for pyridoxine-dependent epilepsies); (ii) avoid antiepileptic drugs (AEDs) that can aggravate the pathogenic defect (e.g., sodium channel blocking drugs in SCN1A-related Dravet syndrome), or (iii) select AEDs that counteract the functional disturbance caused by the gene mutation (e.g., sodium channel blockers for epilepsies due to gain-of-function SCN8A mutations). In some instances, different pathogenic variants of the same gene can have opposite functional effects, which determines whether certain treatments can be beneficial or deleterious (e.g., gain-of-function versus loss-of-function variants in SCN2A determine whether sodium channel blockers improve or worsen seizure control). There are also cases where functional disturbances caused by the gene defect may not be corrected by existing AEDs, but can be countered by medications already available in the market for other indications (e.g., memantine has been used to treat the epileptic encephalopathy caused by a specific gain-of-function GRIN2A mutation), thus making 'drug repurposing' a valuable tool for personalized epilepsy therapies. As our understanding of pathogenic mechanisms improve, opportunities arise for development of treatments targeting the specific gene defect or its consequences. Everolimus, an mTOR inhibitor approved for the treatment of focal seizures associated with tuberous sclerosis complex, is an example of a medication targeting the etiological mechanisms of the disease. Several treatments aimed at correcting specific pathogenic defects responsible for rare genetic epilepsies are currently in development, and range from traditional small molecules to novel approaches involving peptides, antisense oligonucleotides, and gene therapy.
4.
Wilson disease and related copper disorders.
Lorincz, MT
Handbook of clinical neurology. 2018;:279-292
Abstract
Copper is a required cofactor for enzymes in critical metabolic pathways. Mutations in copper metabolism genes or abnormalities in copper metabolism result in disease from copper excess or deficiency. Wilson disease (WD) is an autosomal-recessive disease caused by mutations in the ATP7B gene which encodes a copper-transporting ATPase. Over 500 different WD mutations throughout the ATP7B gene have been described, most of which are missense mutations. Mutations in both ATP7B alleles result in abnormal copper metabolism and subsequent toxic accumulation of copper. The clinical manifestations of neurologic WD include variable combinations of dysarthria, dystonia, tremor, and choreoathetosis. Misdiagnosis and delay in treatment are clinically relevant because untreated WD progresses to hepatic failure or severe neurologic disability and death. Treatment can prevent and cure WD. Mutations in a second, closely related copper-transporting ATPase, ATP7A, cause a spectrum of copper deficiency disorders that include Menkes disease, occipital horn syndrome, and ATP7A-related distal motor neuropathy. Two important, nongenetic causes of copper deficiency myeloneuropathy are copper deficiency following gastric bypass or due to excess zinc ingestion, both of which can cause a myeloneuropathy similar to vitamin B12 deficiency. Copper deficiency following gastric bypass is preventable, and identification and elimination of the excess zinc source, most commonly dental cream, can result in recovery.