Laboratory diagnosis of creatine deficiency syndromes: a technical standard and guideline of the American College of Medical Genetics and Genomics.

Disclaimer: These ACMG Standards and Guidelines are intended as an educational resource for clinical laboratory geneticists to help them provide quality clinical laboratory genetic services. Adherence to these standards and guidelines is voluntary and does not necessarily assure a successful medical outcome. These Standards and Guidelines should not be considered inclusive of all proper procedures and tests or exclusive of others that are reasonably directed to obtaining the same results. In determining the propriety of any specific procedure or test, clinical laboratory geneticists should apply their professional judgment to the specific circumstances presented by the patient or specimen. Clinical laboratory geneticists are encouraged to document in the patient's record the rationale for the use of a particular procedure or test, whether or not it is in conformance with these Standards and Guidelines. They also are advised to take notice of the date any particular guideline was adopted, and to consider other relevant medical and scientific information that becomes available after that date. It also would be prudent to consider whether intellectual property interests may restrict the performance of certain tests and other procedures.Cerebral creatine deficiency syndromes are neurometabolic conditions characterized by intellectual disability, seizures, speech delay, and behavioral abnormalities. Several laboratory methods are available for preliminary and confirmatory diagnosis of these conditions, including measurement of creatine and related metabolites in biofluids using liquid chromatography-tandem mass spectrometry or gas chromatography-mass spectrometry, enzyme activity assays in cultured cells, and DNA sequence analysis. These guidelines are intended to standardize these procedures to help optimize the diagnosis of creatine deficiency syndromes. While biochemical methods are emphasized, considerations for confirmatory molecular testing are also discussed, along with variables that influence test results and interpretation.Genet Med 19 2, 256-263.

Biosynthesis of homoarginine (hArg) and asymmetric dimethylarginine (ADMA) from acutely and chronically administered free L-arginine in humans.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis, whereas L-arginine (Arg) and L-homoarginine (hArg) serve as substrates for NO synthesis. ADMA and other methylated arginines are generally believed to exclusively derive from guanidine (N (G))-methylated arginine residues in proteins by protein arginine methyltransferases (PRMTs) that use S-adenosylmethionine (SAM) as the methyl donor. L-Lysine is known for decades as a precursor for hArg, but only recent studies indicate that arginine:glycine amidinotransferase (AGAT) is responsible for the synthesis of hArg. AGAT catalyzes the formation of guanidinoacetate (GAA) that is methylated to creatine by guanidinoacetate methyltransferase (GAMT) which also uses SAM. The aim of the present study was to learn more about the mechanisms of ADMA and hArg formation in humans. Especially, we hypothesized that ADMA is produced by N (G)-methylation of free Arg in addition to the known PRMTs-involving mechanism. In knockout mouse models of AGAT- and GAMT-deficiency, we investigated the contribution of these enzymes to hArg synthesis. Arg infusion (0.5 g/kg, 30 min) in children (n = 11) and ingestion of high-fat protein meals by overweight men (n = 10) were used to study acute effects on ADMA and hArg synthesis. Daily Arg ingestion (10 g) or placebo for 3 or 6 months by patients suffering from peripheral arterial occlusive disease (PAOD, n = 20) or coronary artery disease (CAD, n = 30) was used to study chronic effects of Arg on ADMA synthesis. Mass spectrometric methods were used to measure all biochemical parameters in plasma and urine samples. In mice, AGAT but not GAMT was found to contribute to plasma hArg, while ADMA synthesis was independent of AGAT and GAMT. Arg infusion acutely increased plasma Arg, hArg and ADMA concentrations, but decreased the plasma hArg/ADMA ratio. High-fat protein meals acutely increased plasma Arg, hArg, ADMA concentrations, as well as the plasma hArg/ADMA ratio. In the PAOD and CAD studies, plasma Arg concentration increased in the verum compared to the placebo groups. Plasma ADMA concentration increased only in the PAOD patients who received Arg. Our study suggests that in humans a minor fraction of free Arg is rapidly metabolized to ADMA and hArg. In mice, GAMT and N (G)-methyltransferases contribute to ADMA and hArg synthesis from Arg, whereas AGAT is involved in the synthesis of hArg but not of ADMA. The underlying biochemical mechanisms remain still elusive.

Feasibility of newborn screening for guanidinoacetate methyltransferase (GAMT) deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency causes brain creatine deficiency characterized by developmental delays, speech delay, seizures and autism-like behavior. Identification and therapy at birth because of a positive family history has prevented intellectual disability and seizures in all cases reported. The objective of this study was to develop a method to identify patients with GAMT deficiency from newborn screening blood spots. Creatine and guanidinoacetate were extracted from 10,000 deidentified blood spots using the same protocol routinely used for newborn screening and quantified by stable isotope dilution using deuterated creatine and guanidinoacetate as internal standards. Residual dried blood spots from three infants with GAMT deficiency were used to evaluate the sensitivity of the method. A second tier test using UPLC-MS/MS was performed to analyze samples with a concentration of guanidinoacetate >2.44 µmol/L (99.5th centile of the normal population). Fifty four blood spots required second tier testing in addition to seven blood spots from three patients with GAMT deficiency retrospectively analyzed. With second tier testing, only the samples from GAMT deficiency patients had elevated concentration of guanidinoacetate. Our results show that GAMT deficiency can be identified in newborns using routine extraction methods. The cost of this additional screening is minimal, as it does not require additional instrumentation, procedure, or sample collection. The use of a second tier test can reduce the false positive rate to a minimum. Summary Brain creatine deficiency syndromes cause mental retardation that can be prevented if therapy is initiated early in life. This manuscript reports that infants with GAMT deficiency (one of the brain creatine deficiency syndromes) can be identified from elevated guanidinoacetate in newborn blood spots with virtually absent false-positive results using a second tier test.

Elevation of guanidinoacetate in newborn dried blood spots and impact of early treatment in GAMT deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is a good candidate disorder for newborn screening because early treatment appears to improve outcomes. We report elevation of guanidinoacetate in archived newborn dried blood spots for 3 cases (2 families) of GAMT deficiency compared with an unaffected carrier and controls. We also report a new case of a patient treated from birth with normal developmental outcome at the age of 42 months.

Guanidinoacetate methyltransferase deficiency: first steps to newborn screening for a treatable neurometabolic disease.

BACKGROUND: GAMT deficiency is an autosomal recessive disorder of creatine biosynthesis resulting in severe neurological complications in untreated patients. Currently available treatment is only successful to stop disease progression, but is not sufficient to reverse neurological complications occurring prior to diagnosis. Normal neurodevelopmental outcome in a patient, treated in the newborn period, highlights the importance of early diagnosis. METHODS: Targeted mutation analysis (c.59G>C and c.327G>A) in the GAMT gene by the QIAxcel system and GAA measurement by a novel two-tier method were performed in 3000 anonymized newborn blood dot spot cards. RESULTS: None of the targeted mutations were detected in any newborn. Two novel heterozygous variants (c.283_285dupGTC; p.Val95dup and c.278_283delinsCTCGATGCAC; p.Asp93AlafsX35) were identified by coincidence. Carrier frequency for these insertion/deletion types of GAMT mutations was 1/1475 in this small cohort of newborns. GAA levels were at or above the 99th percentile (3.12 µmol/l) in 4 newborns. Second-tier testing showed normal results for 4 newborns revealing 0.1% false positive rate. No GAMT mutations were identified in 4 of the newborns with elevated GAA levels in the first tier testing. CONCLUSION: This is the first two-tier study to investigate carrier frequency of GAMT deficiency in the small cohort of newborn population to establish evidence base for the first steps toward newborn screening for this treatable neurometabolic disorder.

Sex-specific associations between umbilical cord blood testosterone levels and language delay in early childhood.

BACKGROUND: Preliminary evidence suggests that prenatal testosterone exposure may be associated with language delay. However, no study has examined a large sample of children at multiple time-points. METHODS: Umbilical cord blood samples were obtained at 861 births and analysed for bioavailable testosterone (BioT) concentrations. When participating offspring were 1, 2 and 3 years of age, parents of 767 children (males = 395; females = 372) completed the Infant Monitoring Questionnaire (IMQ), which measures Communication, Gross Motor, Fine Motor, Adaptive and Personal-Social development. Cut-off scores are available for each scale at each age to identify children with 'clinically significant' developmental delays. Chi-square analyses and generalized estimating equations examined longitudinal associations between sex-specific quartiles of BioT concentrations and the rate of developmental delay. RESULTS: Significantly more males than females had language delay (Communication scale) at age 1, 2 and 3 years (p-values ≤. 01). Males were also more likely to be classified as delayed on the Fine-Motor (p = .04) and Personal-Social (p < .01) scales at age 3 years. Chi-square analyses found a significant difference between BioT quartiles in the rate of language delay (but not Fine-Motor and Personal-Social delay) for males (age 3) and females (age 1 and 3). Generalized estimating equations, incorporating a range of sociodemographic and obstetric variables, found that males in the highest BioT quartile were at increased risk for a clinically significant language delay during the first 3 years of life, with an odds ratio (OR) of 2.47 (95% CI: 1.12, 5.47). By contrast, increasing levels of BioT reduced the risk of language delay among females (Quartile 2: OR = 0.23, 95% CI: 0.09, 0.59; Quartile 4: 0.46, 95% CI: 0.21, 0.99). CONCLUSION: These data suggest that high prenatal testosterone levels are a risk factor for language delay in males, but may be a protective factor for females.

[Characterization of language disorders in children with lead poisoning]. / Caracterização das alterações de linguagem em crianças com histórico de intoxicação por chumbo.

BACKGROUND: lead poisoning can have a negative impact on the neuropsychological functions, including language, due to the damage it causes to the development of the Central Nervous System. AIM: to verify the occurrence of language disorders in children who suffered from led poisoning and to verify the correlation between the lead concentration level in the blood and the language disorders presented by the children. METHOD: language evaluation of 20 preschoolers, with lead concentration level in the blood above 10 microg/dl. RESULTS: 13 children presented language impairment involving only phonology or more than one language subsystem. The statistical analysis indicated that no correlation exists between the severity of the language impairment and the concentration levels of lead. CONCLUSION: the number of children with language impairment indicates lead poisoning as a risk factor for the present alterations, even though other risk factors for language disorders were found and the absence of correlation between the investigated variables.

Hyperserotonemia in adults with autistic disorder.

Hyperserotonemia is the most consistent serotonin-related finding in autism. The basis of this phenomenon, and its relationship to the central serotonergic dysfunction remains unclear. Platelet serotonin level (PSL) in 53 autistic adults and 45 healthy controls was measured. Mean PSL in autistic group (75.7 +/- 37.4 ng/microL) was significantly higher than the control sample (59.2 +/- 16.2 ng/microL) due to a presence of hyperserotonemic subjects which comprised 32% of the patients. PSL of autistic subjects did not correlate with the severity of symptoms, as measured by total CARS score, or the degree of mental retardation. However, significant negative relationship was observed between PSL and speech development, indicating the relationship between the peripheral 5HT concentrations and verbal abilities in autistic subjects.

Corticosterone modulates auditory gating in mouse.

Previous studies suggest that circulating glucocorticoids may influence the encoding and processing of sensory stimuli. The current study investigated this hypothesis by measuring the generation (amplitude), gating (recovery cycle), and sensitivity (intensity function) of auditory evoked responses in C57BL/6 mice treated with chronic corticosterone (0, 1, 5, 15, or 30 mg/kg/day for 14 days). We found that low-dose corticosterone (5 but not 1 mg/kg/day) enhanced the amplitude and improved gating of evoked potentials without affecting the intensity function. In comparison, higher doses (15 and 30 mg/kg/day) decreased the amplitude and impaired gating of evoked potentials, also without altering the stimulus intensity function. At all doses, lower amplitudes of evoked potentials were significantly correlated with higher circulating corticosterone levels. These data highlight the need to consider serum glucocorticoid levels when assessing human disease states associated with aberrations of information processing such as schizophrenia and depression.

The defining DNA methylation signature of Floating-Harbor Syndrome.

Floating-Harbor syndrome (FHS) is an autosomal dominant genetic condition characterized by short stature, delayed osseous maturation, expressive language impairment, and unique facial dysmorphology. We previously identified mutations in the chromatin remodeling protein SRCAP (SNF2-related CBP Activator Protein) as the cause of FHS. SRCAP has multiple roles in chromatin and transcriptional regulation; however, specific epigenetic consequences of SRCAP mutations remain to be described. Using high resolution genome-wide DNA methylation analysis, we identified a unique and highly specific DNA methylation "epi-signature" in the peripheral blood of individuals with FHS. Both hyper and hypomethylated loci are distributed across the genome, preferentially occurring in CpG islands. Clonal bisulfite sequencing of two hypermethylated (FIGN and STPG2) and two hypomethylated (MYO1F and RASIP1) genes confirmed these findings. The identification of a unique methylation signature in FHS provides further insight into the biological function of SRCAP and provides a unique biomarker for this disorder.

Mutations in the AUH gene cause 3-methylglutaconic aciduria type I.

The conversion of 3-methylglutaconyl-CoA to 3-hydroxy-3-methylglutaryl-CoA is the only step in leucine catametabolism yet to be characterized at enzyme and DNA levels. The deficiency of the putative mitochondrial enzyme 3-methylglutaconyl-CoA hydratase associates with the rare organic aciduria 3-methylglutaconic aciduria type I (MGA1), but neither the enzyme nor its gene have been described in any organism. Here we report that human 3-methylglutaconyl-CoA hydratase is identical with a previously described RNA-binding protein (designated AUH) possessing enoyl-CoA hydratase activity. Molecular analyses in five patients from four independent families revealed homozygosity or compound heterozygosity for mutations in the AUH gene; most mutations are predicted to completely abolish protein function. Mutations identified include c.80delG, R197X, IVS8-1G>A, A240V, and c.613_614insA. Clinical severity of MGA1 in published patients has been quite variable. Included in the present study is an additional patient with MGA1 who was detected by neonatal screening and has remained asymptomatic up to his present age of 2 years. The boy is homozygous for an N-terminal frameshift mutation in the AUH gene. Complete absence of 3-methylglutaconyl-CoA hydratase/AUH appears to be compatible with normal development in some cases. Further work is required to identify external or genetic factors associated with development of clinical problems in patients with MGA1.

Kinetics of 3H-serotonin uptake by platelets in infantile autism and developmental language disorder (including five pairs of twins).

The kinetics of 5-HT uptake by platelets was studied in cases of infantile autism and developmental language disorder (DLD) and normal subjects. Two patients of the autism group were twins, and the seven patients of the DLD group were members of four pairs of twins. The Vmax values (means +/- SD) for autism and DLD were 6.46 +/- .90 pmol 5-HT/10(7) cells/min and 4.85 +/- 1.50 pmol 5-HT/10(7) cells/min, respectively. These values were both significantly higher than that of 2.25 +/- .97 pmole 5-HT/10(7) cells/min for normal children. The Km values of the three groups were not significantly different. Data on the five pairs of twins examined suggested that the elevated Vmax of 5-HT uptake by platelets was determined genetically.

Blood serotonin levels in adults, autistic and non-autistic children--with a comparison of different methodologies.

Recent interest in conditions associated with increased blood serotonin level has highlighted the need for consistency between assay methods to allow for more accurate delineation of serotonin variables. To this end, comparison was made between a spectrofluorimetric technique frequently used in the past and two potentially more specific high performance liquid chromatographic procedures. Normal ranges and diurnal variations for blood serotonin in adults, normal, autistic children and children with developmental dysphasia were also determined. No significant difference was found between serotonin level in blood drawn by simultaneous venepuncture and capillary (fingerprick) collection. Whilst there was no evidence of circadian rhythm, seasonal variation with mean blood serotonin levels significantly lower in summer than in two successive winters was suggested. Blood serotonin values in normal children tended to decline with increasing age. No similar maturational effect was apparent in autistic children. The mean level for autistic children in winter was significantly higher than that for normal children in the same season; despite this there was considerable overlap of blood serotonin levels between normal and autistic groups. Serotonin levels determined by the three different methodologies showed a high correlation but differed significantly: caution should be exercised when comparing blood serotonin results where different methods are employed.

An explanation for the association between specific language impairment and toxemia.

An association between specific language impairment (SLI) and toxemia has been detected in several studies. No clear explanation for this association has been identified to date. However, a number of potential explanations have been offered. These include: (1) toxemia causes fetal anoxia which leads to brain damage; (2) toxemia in the mother is an indication of maternal immune attack on the developing brain; (3) the association between toxemia and SLI is indirect and arises because both are consequences of a common but as yet unknown etiological factor. In this paper we present a fourth possible explanation for the association. That is, that both SLI and toxemia may be the consequence of low circulating levels of essential fatty acids. Evidence supporting this hypothesis is presented and four possible mechanisms underlying the association are discussed.

Stable isotope dilution microquantification of creatine metabolites in plasma, whole blood and dried blood spots for pharmacological studies in mouse models of creatine deficiency.

BACKGROUND: To develop an accurate stable isotope dilution assay for simultaneous quantification of creatine metabolites ornithine, arginine, creatine, creatinine, and guanidinoacetate in very small blood sample volumes to study creatine metabolism in mice. METHODS: Liquid-chromatography (C18) tandem mass spectrometry with butylation was performed in positive ionization mode. Stable isotope dilution assay with external calibration was applied to three different specimen types, plasma, whole blood and dried blood spot (DBS). RESULTS: Analytical separation, sensitivity, accuracy, and linearity of the assay were adequate. The stable isotope dilution assay in plasma revealed no significant bias to gold standard methods for the respective analytes. Compared to plasma, we observed an overestimate of creatine and creatinine (2- to 5-fold and 1.2- to 2-fold, respectively) in whole-blood and DBS, and an underestimate of arginine (2.5-fold) in DBS. Validation of the assay in mouse models of creatine deficiency revealed plasma creatine metabolite pattern in good accordance with those observed in human GAMT and AGAT deficiency. Single dose intraperitoneal application of ornithine in wild-type mice lead to fast ornithine uptake (Tmax ≤ 10 min) and elimination (T1/2=24 min), and a decline of guanidinoacetate. CONCLUSION: The assay is fast and reliable to study creatine metabolism and pharmacokinetics in mouse models of creatine deficiency.

Blood-based gene expression signatures of infants and toddlers with autism.

OBJECTIVE: Autism spectrum disorders (ASDs) are highly heritable neurodevelopmental disorders that onset clinically during the first years of life. ASD risk biomarkers expressed early in life could significantly impact diagnosis and treatment, but no transcriptome-wide biomarker classifiers derived from fresh blood samples from children with autism have yet emerged. METHOD: Using a community-based, prospective, longitudinal method, we identified 60 infants and toddlers at risk for ASDs (autistic disorder and pervasive developmental disorder), 34 at-risk for language delay, 17 at-risk for global developmental delay, and 68 typically developing comparison children. Diagnoses were confirmed via longitudinal follow-up. Each child's mRNA expression profile in peripheral blood mononuclear cells was determined by microarray. RESULTS: Potential ASD biomarkers were discovered in one-half of the sample and used to build a classifier, with high diagnostic accuracy in the remaining half of the sample. CONCLUSIONS: The mRNA expression abnormalities reliably observed in peripheral blood mononuclear cells, which are safely and easily assayed in infants, offer the first potential peripheral blood-based, early biomarker panel of risk for autism in infants and toddlers. Future work should verify these biomarkers and evaluate whether they may also serve as indirect indices of deviant molecular neural mechanisms in autism.

Hyperbilirubinemia and language delay in premature infants.

OBJECTIVE: Our goal was to evaluate whether language delay at 3 years in premature infants is associated with previous exposure to hyperbilirubinemia during the first 2 weeks after birth. PATIENTS AND METHODS: We performed a retrospective case-control study of infants admitted to the NICU between January and October 2003. Inclusion criteria included a birth weight of < or =1500 g and follow-up to age 3 years. Exclusion criteria included genetic disorders and hearing loss or recurrent ear infections. Peak total serum bilirubin levels during the first 2 weeks and duration of hyperbilirubinemia (days with total serum bilirubin level at >8 mg/dL) were determined. Infants with language delay and who were receiving speech therapy by 3 years were identified through developmental clinic charts and a tracking program and compared with infants who had normal language development. RESULTS: A total of 125 infants with birth weight of < or =1500 g were admitted to the NICU between January and October 2003. Fifteen infants died, and 110 were discharged from the hospital. A total of 102 (93%) of 110 infants had follow-up to the age of 3 years. Four infants were excluded (1 genetic disorder, 3 delayed hearing loss or recurrent ear infections). Twenty-four infants had a language delay and received speech therapy, whereas 74 infants had normal language development. There was no significant difference in peak total serum bilirubin level and duration of hyperbilirubinemia between the 2 groups. On logistic regression, only bronchopulmonary dysplasia was associated with language delay. CONCLUSIONS: Hyperbilirubinemia, defined as peak total serum bilirubin level or duration of elevated bilirubin in days, is not associated with language delay in premature infants. However, this issue deserves investigation, because other measures of bilirubin, such as unbound bilirubin, may be associated with language delay.

Caracterização das alterações de linguagem em crianças com histórico de intoxicação por chumbo / Characterization of language disorders in children with lead poisoning

TEMA: a intoxicação por chumbo pode causar deficiências neuropsicológicas, que incluem a linguagem, devido aos danos provocados no desenvolvimento do SNC. OBJETIVO: verificar a ocorrência de alterações de linguagem em crianças com histórico de intoxicação por chumbo e a correlação entre o índice de chumbo sangüíneo e as alterações de linguagem apresentadas pelas crianças. MÉTODO: avaliação da linguagem de 20 crianças em idade pré-escolar, com índice de chumbo sangüíneo acima de 10 µg/dl. RESULTADOS: 13 crianças apresentaram distúrbio de linguagem envolvendo somente a Fonologia ou mais de um subsistema lingüístico. A análise estatistica revelou não existir correlação entre a gravidade das alterações e os índices de chumbo apresentado. CONCLUSÃO: a ocorrência de crianças com distúrbio de linguagem aponta a contaminação por chumbo como um fator de risco para as alterações apresentadas, mesmo tendo sido encontrados outros fatores que levem à defasagem no desenvolvimento da linguagem e ausência de correlação entre as referidas variavéis.

BACKGROUND: lead poisoning can have a negative impact on the neuropsychological functions, including language, due to the damage it causes to the development of the Central Nervous System. AIM: to verify the occurrence of language disorders in children who suffered from led poisoning and to verify the correlation between the lead concentration level in the blood and the language disorders presented by the children. METHOD: language evaluation of 20 preschoolers, with lead concentration level in the blood above 10µg/dl. RESULTS: 13 children presented language impairment involving only phonology or more than one language subsystem. The statistical analysis indicated that no correlation exists between the severity of the language impairment and the concentration levels of lead. CONCLUSION: the number of children with language impairment indicates lead poisoning as a risk factor for the present alterations, even though other risk factors for language disorders were found and the absence of correlation between the investigated variables.