Rationale and design of the Baylor Infant Twin Study-A study assessing obesity-related risk factors from infancy.

BACKGROUND: Early childhood (0-3 years) is a critical period for obesity prevention, when tendencies in eating behaviors and physical activity are established. Yet, little is understood about how the environment shapes children's genetic predisposition for these behaviors during this time. The Baylor Infant Twin Study (BITS) is a two phase study, initiated to study obesity risk factors from infancy. Data collection has been completed for Phase 1 in which three sub-studies pilot central measures for Phase 2. A novel infant temperament assessment, based on observations made by trained researchers was piloted in Behavior Observation Pilot Protocol (BOPP) study, a new device for measuring infant feeding parameters (the "orometer") in the Baylor Infant Orometer (BIO), and methods for analyzing DNA methylation in twins of unknown chorionicity in EpiTwin. METHODS: EpiTwin was a cross-sectional study of neonatal twins, while up to three study visits occurred for the other studies, at 4- (BOPP, BIO), 6- (BOPP), and 12- (BOPP, BIO) of age. Measurements for BOPP and BIO included temperament observations, feeding observations, and body composition assessments while EpiTwin focused on collecting samples of hair, urine, nails, and blood for quantifying methylation levels at 10 metastable epialleles. Additional data collected include demographic information, zygosity, chorionicity, and questionnaire-based measures of infant behaviors. RESULTS: Recruitment for all three studies was completed in early 2020. EpiTwin recruited 80 twin pairs (50% monochorionic), 31 twin pairs completed the BOPP protocol, and 68 singleton infants participated in BIO. CONCLUSIONS: The psychometric properties of the data from all three studies are being analyzed currently. The resulting findings will inform the development of the full BITS protocol, with the goal of completing assessments at 4-, 6-, 12-, and 14-month of age for 400 twin pairs.

Round Table Discussion.

The 1st International Carnitine Working Group concluded with a round table discussion addressing several areas of relevance. These included the design of future studies that could increase the amount of evidence-based data about the role of carnitine in the treatment of fatty acid oxidation defects, for which substantial controversy still exists. There was general consensus that future trials on the effect of carnitine in disorders of fatty acid oxidation should be randomized, double-blinded, multicentered and minimally include the following diagnoses: medium-chain acyl coenzyme A (CoA) dehydrogenase deficiency, very long-chain acyl-CoA dehydrogenase deficiency, long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and mitochondrial trifunctional protein deficiency. Another area that generated interest was trials of carnitine in cardiomyopathy and, especially, the use of biomarkers to identify patients at greater risk of cardiotoxicity following treatment with anthracyclines. The possibility that carnitine treatment may lead to improvements in autistic behaviors was also discussed, although the evidence is still not sufficient to make any firm conclusions in this regard. Preliminary data on carnitine levels in children and adolescents with primary hypertension, low birth weight and nephrotic syndrome was also presented. Lastly, the panelists stressed that there remains an objective need to harmonize the terminology used to describe carnitine deficiencies (e.g., primary, secondary and systemic deficiency).

Historical Perspective on Clinical Trials of Carnitine in Children and Adults.

The metabolic roles of carnitine have been greatly clarified over the past 50 years, and it is now well established that carnitine is a key player in mitochondrial generation of energy and metabolism of acetyl coenzyme A. A therapeutic role for carnitine in treatment of nutritional deficiencies in infants and children was first demonstrated in 1958, and since that time it has been used to treat a number of inborn errors of metabolism. Carnitine was approved by the US Food and Drug Administration in 1985 for treatment of 'primary carnitine deficiency', and later in 1992 for treatment of 'secondary carnitine deficiency', a definition that included the majority of relevant metabolic disorders associated with low or abnormal plasma carnitine levels. Today, carnitine treatment of inborn errors of metabolism is a safe and integral part of many treatment protocols, and a growing interest in carnitine has resulted in greater recognition of many causes of carnitine depletion. Notwithstanding, there is still a lack of data from randomized clinical trials, even on the use of carnitine in inborn errors of metabolism, although ethical issues may be a contributing factor in this regard.

Quantification of intraoral pressures during nutritive sucking: methods with normal infants.

We report quantitative measurements of ten parameters of nutritive sucking behavior in 91 normal full-term infants obtained using a novel device (an Orometer) and a data collection/analytical system (Suck Editor). The sucking parameters assessed include the number of sucks, mean pressure amplitude of sucks, mean frequency of sucks per second, mean suck interval in seconds, sucking amplitude variability, suck interval variability, number of suck bursts, mean number of sucks per suck burst, mean suck burst duration, and mean interburst gap duration. For analyses, test sessions were divided into 4 × 2-min segments. In single-study tests, 36 of 60 possible comparisons of ten parameters over six pairs of 2-min time intervals showed a p value of 0.05 or less. In 15 paired tests in the same infants at different ages, 33 of 50 possible comparisons of ten parameters over five time intervals showed p values of 0.05 or less. Quantification of nutritive sucking is feasible, showing statistically valid results for ten parameters that change during a feed and with age. These findings suggest that further research, based on our approach, may show clinical value in feeding assessment, diagnosis, and clinical management.

IDH2 mutations in patients with D-2-hydroxyglutaric aciduria.

Heterozygous somatic mutations in the genes encoding isocitrate dehydrogenase-1 and -2 (IDH1 and IDH2) were recently discovered in human neoplastic disorders. These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG). We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA), a rare neurometabolic disorder characterized by supraphysiological levels of D-2-HG. These findings provide additional impetus for investigating the role of D-2-HG in the pathophysiology of metabolic disease and cancer.

Contrasting phenotypes in three patients with novel mutations in mitochondrial tRNA genes.

We studied three patients, each harboring a novel mutation at a highly conserved position in a different mitochondrial tRNA gene. The mutation in patient 1 (T5543C) was associated with isolated mitochondrial myopathy, and occurred in the anticodon loop of tRNA(Trp). In patient 2, with mitochondrial myopathy and marked retinopathy, the mutation (G14710A) resulted in an anticodon swap (Glu to Lys) in tRNA(Glu). Patient 3, who manifested mitochondrial encephalomyopathy and moderate retinal dysfunction, harbored a mutation (C3287A) in the TpsiC loop of tRNA(Leu(UUR)). The mutations were heteroplasmic in muscle in all cases, and sporadic in two cases. PCR-RFLP analysis in all patients showed much higher amounts of mutated mtDNA in affected tissue (muscle) than unaffected tissue (blood), and significantly higher levels of mutated mtDNA in cytochrome c oxidase (COX)-negative muscle fibers than in COX-positive fibers, confirming the pathogenicity of these mutations. The mutation was also detected in single hair roots from all three patients, indicating that each mutation must have arisen early in embryonic development or in maternal germ cells. This suggests that individual hair root analyses may reflect a wider tissue distribution of mutated mtDNA than is clinically apparent, and might be useful in predicting prognosis and, perhaps, the risk of transmitting the mutation to offspring. Our data suggest a correlation between clinical phenotype and distribution of mutated mtDNA in muscle versus hair roots. Furthermore, the high threshold for phenotypic expression in single muscle fibers (92-96%) suggests that therapies may only need to increase the percentage of wild-type mtDNA by a small amount to be beneficial.

Metabolic evaluation of infantile epilepsy: summary recommendations of the Amalfi Group.

The purpose of this symposium was to bring together the disciplines of clinical neurology and metabolic investigation and to present the most up-to-date information about specific metabolic disorders associated with infantile epilepsy. Understanding the etiology of seizures is the key to rational intervention. It is only with this insight that progress in the treatment of these patients can be made. In the past, many infantile epileptic syndromes were described by their clinical features, without understanding of the underlying pathophysiology. In the future, it is hoped that the genetic and metabolic bases of these syndromes will be more completely defined such that reliable diagnostic and effective treatment methods are available. Most of the tests listed in Table 2 should not be performed without due consideration of the history, clinical findings, and results of prior studies. This article is intended to aid clinicians in reviewing potential metabolic diagnoses and to approaching metabolic evaluations in an economical, logical, and comprehensive manner. Although the field of metabolic diseases may be in its infancy, many of these disorders can be identified and treated. The task for investigators is to provide the armamentarium of diagnostic tools to clinicians to ensure that a metabolic disorder is not overlooked. There must be a common ground that links clinicians and basic researchers in an evolving and collaborative manner.