Targeted-Capture Next-Generation Sequencing in Diagnosis Approach of Pediatric Cholestasis.

BACKGROUND: Cholestasis is a frequent and severe condition during childhood. Genetic cholestatic diseases represent up to 25% of pediatric cholestasis. Molecular analysis by targeted-capture next generation sequencing (NGS) has recently emerged as an efficient diagnostic tool. The objective of this study is to evaluate the use of NGS in children with cholestasis. METHODS: Children presenting cholestasis were included between 2015 and 2020. Molecular sequencing was performed by targeted capture of a panel of 34 genes involved in cholestasis and jaundice. Patients were classified into three categories: certain diagnosis; suggested diagnosis (when genotype was consistent with phenotype for conditions without any available OMIM or ORPHANET-number); uncertain diagnosis (when clinical and para-clinical findings were not consistent enough with molecular findings). RESULTS: A certain diagnosis was established in 169 patients among the 602 included (28.1%). Molecular studies led to a suggested diagnosis in 40 patients (6.6%) and to an uncertain diagnosis in 21 patients (3.5%). In 372 children (61.7%), no molecular defect was identified. CONCLUSIONS: NGS is a useful diagnostic tool in pediatric cholestasis, providing a certain diagnosis in 28.1% of the patients included in this study. In the remaining patients, especially those with variants of uncertain significance, the imputability of the variants requires further investigations.

Fluxomic assay-assisted diagnosis orientation in a cohort of 11 patients with myopathic form of CPT2 deficiency.

Carnitine palmitoyltransferase type 2 (CPT2) deficiency, a mitochondrial fatty acid oxidation disorder (MFAOD), is a cause of myopathy in its late clinical presentation. As for other MFAODs, its diagnosis may be evocated when blood acylcarnitine profile is abnormal. However, a lack of abnormalities or specificity in this profile is not exclusive of CPT2 deficiency. Our retrospective study reports clinical and biological data in a cohort of 11 patients with circulating acylcarnitine profile unconclusive enough for a specific diagnosis orientation. In these patients, CPT2 gene studies was prompted by prior fluxomic explorations of mitochondrial ß-oxidation on intact whole blood cells incubated with pentadeuterated ([16-2H3, 15-2H2])-palmitate. Clinical indication for fluxomic explorations was at least one acute rhabdomyolysis episode complicated, in 5 of 11 patients, by acute renal failure. Major trigger of rhabdomyolysis was febrile infection. In all patients, fluxomic data indicated deficient CPT2 function showing normal deuterated palmitoylcarnitine (C16-Cn) formation rates associated with increased ratios between generated C16-Cn and downstream deuterated metabolites (Σ deuterated C2-Cn to C14-Cn). Subsequent gene studies showed in all patients pathogenic gene variants in either homozygous or compound heterozygous forms. Consistent with literature data, allelic frequency of the c.338C > T[p.Ser113Leu] mutation amounted to 68.2% in our cohort. Other missense mutations included c.149C > A[p.Pro50His] (9%), c.200C > G[p.Ala200Gly] (4.5%) and previously unreported c.1171A > G[p.ser391Gly] (4.5%) and c.1420G > C[p.Ala474Pro] (4.5%) mutations. Frameshift c.1666-1667delTT[p.Leu556val*16] mutation (9%) was observed in two patients unknown to be related.

Fluxomic evidence for impaired contribution of short-chain acyl-CoA dehydrogenase to mitochondrial palmitate ß-oxidation in symptomatic patients with ACADS gene susceptibility variants.

BACKGROUND: Despite ACADS (acyl-CoA dehydrogenase, short-chain) gene susceptibility variants (c.511C>T and c.625G>A) are considered to be non-pathogenic, encoded proteins are known to exhibit altered kinetics. Whether or not, they might affect overall fatty acid ß-oxidation still remains, however, unclear. METHODS: De novo biosynthesis of acylcarnitines by whole blood samples incubated with deuterated palmitate (16-2H3,15-2H2-palmitate) is suitable as a fluxomic exploration to distinguish between normal and disrupted ß-oxidation, abnormal profiles and ratios of acylcarnitines with different chain-lengths being indicative of the site for enzymatic blockade. Determinations in 301 control subjects of ratios between deuterated butyrylcarnitine and sum of deuterated C2 to C14 acylcarnitines served here as reference values to state specifically functional SCAD impairment in patients addressed for clinical and/or biological suspicion of a ß-oxidation disorder. RESULTS: Functional SCAD impairment was found in 39 patients. The 27 patients accepting subsequent gene studies were all positive for ACADS mutations. Twenty-six of 27 patients were positive for c.625G>A variant. Twenty-three of 27 patients harbored susceptibility variants as sole ACADS alterations (18 homozygous and 3 heterozygous for c.625G>A, 2 compound heterozygous for c.625G>A/c.511C>T). CONCLUSION: Our present fluxomic assessment of SCAD suggests a link between ACADS susceptibility variants and abnormal ß-oxidation consistent with known altered kinetics of these variants.

A fast method for high resolution oxymetry study of skeletal muscle mitochondrial respiratory chain complexes.

High resolution oxymetry study (HROS) of skeletal muscle usually requires 90-120 min preparative phase (dissection, permeabilization and washing). This work reports on the suitability of a rapid muscle preparation which by-passes this long preparation. For a few seconds only, muscle biopsy from pigs is submitted to gentle homogenization at 8000 rotations per minute using an ultra-dispersor apparatus. Subsequent HROS is performed using FCCP instead of ADP, compounds crossing and not plasma membrane, respectively. This simplified procedure compares favorably with classical (permeabilized fibers) HROS in terms of respiratory chain complex activities. Mitochondria from cells undergoing ultradispersion were functionally preserved as attested by relative inefficacy of added cytochrome C (not crossing intact mitochondrial outer membrane) to stimulate mitochondrial respiration. Responsiveness of respiration to ADP (in the absence of FCCP) suggested that these intact mitochondria were outside cells disrupted by ultradispersion or within cells permeated by this procedure.

Doubling diet fat on sugar ratio in children with mitochondrial OXPHOS disorders: Effects of a randomized trial on resting energy expenditure, diet induced thermogenesis and body composition.

BACKGROUND & AIMS: Mitochondrial OXPHOS disorders (MODs) affect one or several complexes of respiratory chain oxidative phosphorylation. An increased fat/low-carbohydrate ratio of the diet was recommended for treating MODs without, however, evaluating its potential benefits through changes in the respective contributions of cell pathways (glycolysis, fatty acid oxidation) initiating energy production. Therefore, the objective of the present work was to compare Resting Energy Expenditure (REE) under basal diet (BD) and challenging diet (CD) in which fat on sugar content ratio was doubled. Diet-induced thermogenesis (DIT) and body compositions were also compared. Energetic vs regulatory aspects of increasing fat contribution to total nutritional energy input were essentially addressed through measures primarily aiming at modifying total fat amounts and not the types of fats in designed diets. METHODS: In this randomized cross-over study, BD contained 10% proteins/30% lipids/60% carbohydrates (fat on sugar ratio = 0.5) and was the imposed diet at baseline. CD contained 10% proteins/45% lipids/45% carbohydrates (fat on sugar ratio = 1). Main and second evaluation criteria measured by indirect calorimetry (QUARK RMR®, Cosmed, Pavona; Italy) were REE and DIT, respectively. Thirty four MOD patients were included; 22 (mean age 13.2 ± 4.7 years, 50% female; BMI 16.9 ± 4.2 kg/m2) were evaluated for REE, and 12 (mean age 13.8 ± 4.8 years, 60% female; BMI 17.4 ± 4.6 kg/m2) also for DIT. OXPHOS complex deficiency repartition in 22 analysed patients was 55% for complex I, 9% for complex III, 27% for complex IV and 9% for other proteins. RESULTS: Neither carry-over nor period effects were detected (p = 0.878; ANOVA for repeated measures). REE was similar between BD vs CD (1148.8 ± 301.7 vs 1156.1 ± 278.8 kcal/day; p = 0.942) as well as DIT (peak DIT 260 vs 265 kcal/day; p = 0.842) and body composition (21.9 ± 13.0 vs 21.6 ± 13.3% of fat mass; p = 0.810). CONCLUSION: Doubling diet fat on sugar ratio does not appear to improve, per se, energetic status and body composition of patients with MODs.

Creatine biosynthesis and transport in health and disease.

Creatine is physiologically provided equally by diet and by endogenous synthesis from arginine and glycine with successive involvements of arginine glycine amidinotransferase [AGAT] and guanidinoacetate methyl transferase [GAMT]. A specific plasma membrane transporter, creatine transporter [CRTR] (SLC6A8), further enables cells to incorporate creatine and through uptake of its precursor, guanidinoacetate, also directly contributes to creatine biosynthesis. Breakthrough in the role of creatine has arisen from studies on creatine deficiency disorders. Primary creatine disorders are inherited as autosomal recessive (mutations affecting GATM [for glycine-amidinotransferase, mitochondrial]) and GAMT genes) or X-linked (SLC6A8 gene) traits. They have highlighted the role of creatine in brain functions altered in patients (global developmental delay, intellectual disability, behavioral disorders). Creatine modulates GABAergic and glutamatergic cerebral pathways, presynaptic CRTR (SLC6A8) ensuring re-uptake of synaptic creatine. Secondary creatine disorders, addressing other genes, have stressed the extraordinary imbrication of creatine metabolism with many other cellular pathways. This high dependence on multiple pathways supports creatine as a cellular sensor, to cell methylation and energy status. Creatine biosynthesis consumes 40% of methyl groups produced as S-adenosylmethionine, and creatine uptake is controlled by AMP activated protein kinase, a ubiquitous sensor of energy depletion. Today, creatine is considered as a potential sensor of cell methylation and energy status, a neurotransmitter influencing key (GABAergic and glutamatergic) CNS neurotransmission, therapeutic agent with anaplerotic properties (towards creatine kinases [creatine-creatine phosphate cycle] and creatine neurotransmission), energetic and antioxidant compound (benefits in degenerative diseases through protection against energy depletion and oxidant species) with osmolyte behavior (retention of water by muscle). This review encompasses all these aspects by providing an illustrated metabolic account for brain and body creatine in health and disease, an algorithm to diagnose metabolic and gene bases of primary and secondary creatine deficiencies, and a metabolic exploration by (1)H-MRS assessment of cerebral creatine levels and response to therapeutic measures.

Opioid Facilitation of ß-Adrenergic Blockade: A New Pharmacological Condition?

Recently, propranolol was suggested to prevent hyperlactatemia in a child with hypovolemic shock through ß-adrenergic blockade. Though it is a known inhibitor of glycolysis, propranolol, outside this observation, has never been reported to fully protect against lactate overproduction. On the other hand, literature evidence exists for a cross-talk between ß-adrenergic receptors (protein targets of propranolol) and δ-opioid receptor. In this literature context, it is hypothesized here that anti-diarrheic racecadotril (a pro-drug of thiorphan, an inhibitor of enkephalinases), which, in the cited observation, was co-administered with propranolol, might have facilitated the ß-blocker-driven inhibition of glycolysis and resulting lactate production. The opioid-facilitated ß-adrenergic blockade would be essentially additivity or even synergism putatively existing between antagonism of ß-adrenergic receptors and agonism of δ-opioid receptor in lowering cellular cAMP and dependent functions.

Creatine and guanidinoacetate reference values in a French population.

Creatine and guanidinoacetate are biomarkers of creatine metabolism. Their assays in body fluids may be used for detecting patients with primary creatine deficiency disorders (PCDD), a class of inherited diseases. Their laboratory values in blood and urine may vary with age, requiring that reference normal values are given within the age range. Despite the long known role of creatine for muscle physiology, muscle signs are not necessarily the major complaint expressed by PCDD patients. These disorders drastically affect brain function inducing, in patients, intellectual disability, autistic behavior and other neurological signs (delays in speech and language, epilepsy, ataxia, dystonia and choreoathetosis), being a common feature the drop in brain creatine content. For this reason, screening of PCDD patients has been repeatedly carried out in populations with neurological signs. This report is aimed at providing reference laboratory values and related age ranges found for a large scale population of patients with neurological signs (more than 6 thousand patients) previously serving as a background population for screening French patients with PCDD. These reference laboratory values and age ranges compare rather favorably with literature values for healthy populations. Some differences are also observed, and female participants are discriminated from male participants as regards to urine but not blood values including creatine on creatinine ratio and guanidinoacetate on creatinine ratio values. Such gender differences were previously observed in healthy populations; they might be explained by literature differential effects of testosterone and estrogen in adolescents and adults, and by estrogen effects in prepubertal age on SLC6A8 function. Finally, though they were acquired on a population with neurological signs, the present data might reasonably serve as reference laboratory values in any future medical study exploring abnormalities of creatine metabolism and transport.

Five year follow-up of two sisters with type II sialidosis: systemic and ophthalmic findings including OCT analysis.

The authors report a 5-year follow-up examination of two sisters diagnosed as having a juvenile form of type II sialidosis. Diagnosis occurred during a routine ophthalmic examination when the girls were 5 and 3 years old after bilateral macular cherry-red spots were revealed. Main clinical findings were hypotonia, hepatosplenomegaly, hearing loss, dysostosis, and respiratory distress. Ophthalmic symptoms were low visual acuity and nystagmus. Spectral-domain optical coherence tomography examination showed increased reflectivity of the retinal ganglion cells. Sialidosis may present as a mild form with slow progression. The cherry-red spots may be the first clue for proper diagnosis of storage disease. Spectral-domain optical coherence tomography examination unveiled the accumulation of sialic acid in the retinal ganglion cells and could potentially be used to monitor the progression of storage diseases.

Screening for primary creatine deficiencies in French patients with unexplained neurological symptoms.

A population of patients with unexplained neurological symptoms from six major French university hospitals was screened over a 28-month period for primary creatine disorder (PCD). Urine guanidinoacetate (GAA) and creatine:creatinine ratios were measured in a cohort of 6,353 subjects to identify PCD patients and compile their clinical, 1H-MRS, biochemical and molecular data. Six GAMT [N-guanidinoacetatemethyltransferase (EC 2.1.1.2)] and 10 X-linked creatine transporter (SLC6A8) but no AGAT (GATM) [L-arginine/glycine amidinotransferase (EC 2.1.4.1)] deficient patients were identified in this manner. Three additional affected sibs were further identified after familial inquiry (1 brother with GAMT deficiency and 2 brothers with SLC6A8 deficiency in two different families). The prevalence of PCD in this population was 0.25% (0.09% and 0.16% for GAMT and SLC6A8 deficiencies, respectively). Seven new PCD-causing mutations were discovered (2 nonsense [c.577C > T and c.289C > T] and 1 splicing [c.391 + 15G > T] mutations for the GAMT gene and, 2 missense [c.1208C > A and c.926C > A], 1 frameshift [c.930delG] and 1 splicing [c.1393-1G > A] mutations for the SLC6A8 gene). No hot spot mutations were observed in these genes, as all the mutations were distributed throughout the entire gene sequences and were essentially patient/family specific. Approximately one fifth of the mutations of SLC6A8, but not GAMT, were attributed to neo-mutation, germinal or somatic mosaicism events. The only SLC6A8-deficient female patient in our series presented with the severe phenotype usually characterizing affected male patients, an observation in agreement with recent evidence that is in support of the fact that this X-linked disorder might be more frequent than expected in the female population with intellectual disability.

A Novel Mutation in CPT1A Resulting in Hepatic CPT Deficiency.

The present work presents a "from gene defect to clinics" pathogenesis study of a patient with a hitherto unreported mutation in the CPT1A gene. In early childhood, the patient developed a life-threatening episode (hypoketotic hypoglycemia, liver cytolysis, and hepatomegaly) evocative of a mitochondrial fatty acid oxidation disorder, and presented deficient fibroblast carnitine palmitoyltransferase 1 (CPT1) activity and homozygosity for the c.1783 C > T nucleotide substitution on exon 15 of CPT1A (p.R595W mutant). While confirming CPT1A deficiency, whole blood de novo acylcarnitine synthesis and the levels of carnitine and its esters formally linked intracellular free-carnitine depletion to intracellular carnitine esterification. Sequence alignment and modeling of wild-type and p.*R595W CPT1A proteins indicated that the Arg595 targeted by the mutated codon is phylogenetically well conversed. It contributes to a hydrogen bond network with neighboring residues Cys304 and Met593 but does not participate in the catalysis and carnitine pocket. Its replacement by tryptophan induces steric hindrance with the side chain of Ile480 located in α-helix 12, affecting protein architecture and function. This hindrance with Ile480 is also originally described with tryptophan 304 in the known mutant p.C304W CPT1A, suggesting that the mechanisms that invalidate CPT1A activity and underlie pathogenesis could be common in both the new (p.R595W) and previously described (p.C304W) mutants.

A novel mutation of the ACADM gene (c.145C>G) associated with the common c.985A>G mutation on the other ACADM allele causes mild MCAD deficiency: a case report.

A female patient, with normal familial history, developed at the age of 30 months an episode of diarrhoea, vomiting and lethargy which resolved spontaneously. At the age of 3 years, the patient re-iterated vomiting, was sub-febrile and hypoglycemic, fell into coma, developed seizures and sequels involving right hemi-body. Urinary excretion of hexanoylglycine and suberylglycine was low during this metabolic decompensation. A study of pre- and post-prandial blood glucose and ketones over a period of 24 hours showed a normal glycaemic cycle but a failure to form ketones after 12 hours fasting, suggesting a mitochondrial ß-oxidation defect. Total blood carnitine was lowered with unesterified carnitine being half of the lowest control value. A diagnosis of mild MCAD deficiency (MCADD) was based on rates of 1-14C-octanoate and 9, 10-3H-myristate oxidation and of octanoyl-CoA dehydrogenase being reduced to 25% of control values. Other mitochondrial fatty acid oxidation proteins were functionally normal. De novo acylcarnitine synthesis in whole blood samples incubated with deuterated palmitate was also typical of MCADD. Genetic studies showed that the patient was compound heterozygous with a sequence variation in both of the two ACADM alleles; one had the common c.985A>G mutation and the other had a novel c.145C>G mutation. This is the first report for the ACADM gene c.145C>G mutation: it is located in exon 3 and causes a replacement of glutamine to glutamate at position 24 of the mature protein (Q24E). Associated with heterozygosity for c.985A>G mutation, this mutation is responsible for a mild MCADD phenotype along with a clinical story corroborating the emerging literature view that patients with genotypes representing mild MCADD (high residual enzyme activity and low urinary levels of glycine conjugates), similar to some of the mild MCADDs detected by MS/MS newborn screening, may be at risk for disease presentation.

Deuterated palmitate-driven acylcarnitine formation by whole-blood samples for a rapid diagnostic exploration of mitochondrial fatty acid oxidation disorders.

BACKGROUND: The biochemical diagnosis of mitochondrial fatty acid oxidation defects (FAOD) currently rests on enzyme assays. A dynamic ex vivo exploration consisting of incubations of whole-blood samples with stable-labeled palmitate and determining leukocyte capacities to produce deuterated acylcarnitines was developed on healthy controls (n=52) and patients with very-long- (VLCADD) (n=2), medium- (MCADD) (n=6), or short- (SCADD) (n=1) chain acyl-CoA dehydrogenase deficiencies. METHODS: Incubations were optimized with L-carnitine and [16-(2)H(3), 15-(2)H(2)]-palmitate at 37 degrees C for various time periods on MCADD and control whole-blood samples. Labeled acylcarnitines were quantified by electrospray-ionization tandem mass spectrometry after thawing, extraction and derivatization to their butyl esters and the method was applied to patients with defects mentioned above. RESULTS: The production of acylcarnitines was linear until 6 h of incubation and optimal on 50 to 200 nmol deuterated substrate. A good discrimination between MCADD patient and control data was found, with median C8/C4 acylcarnitine production rate ratios of 81.0 (5th-95th percentile range: 16.6-209.9) and 0.21 (5th-95th percentile range: 0.06-0.79), respectively. The method also discriminated from controls the VLCADD and SCADD patients. Preliminary studies on a healthy control indicated that the storage at 4 degrees C does little or not alter capacities of whole-blood samples to generate labeled acylcarnitines over a period of 48 h. CONCLUSION: The rapid management afforded by the method, its abilities to characterize patients and to work on whole-blood samples after a stay of 24-48 h at 4 degrees C make it promising for the diagnostic exploration of FAOD.