Consensus guideline for the diagnosis and treatment of aromatic l-amino acid decarboxylase (AADC) deficiency

Aromatic L-amino acid decarboxylase deficiency (AADCD) is a rare, autosomal recessive neurometabolic disorder that leads to a severe combined deficiency of serotonin, dopamine, norepinephrine and epinephrine. Onset is early in life, and key clinical symptoms are hypotonia, movement disorders (oculogyric crisis, dystonia, and hypokinesia), developmental delay, and autonomic symptoms.In this consensus guideline, representatives of the International Working Group on Neurotransmitter Related Disorders (iNTD) and patient representatives evaluated all available evidence for diagnosis and treatment of AADCD and made recommendations using SIGN and GRADE methodology. In the face of limited definitive evidence, we constructed practical recommendations on clinical diagnosis, laboratory diagnosis, imaging and electroencephalograpy, medical treatments and non-medical treatments. Furthermore, we identified topics for further research. We believe this guideline will improve the care for AADCD patients around the world whilst promoting general awareness of this rare disease.

Reference data for cerebrospinal fluid and the utility of amino acid measurement for the diagnosis of inborn errors of metabolism

Background: Cerebrospinal fluid (CSF) amino acid analysis is fundamental to the investigation of several inherited metabolic diseases, particularly those presenting with unexplained seizures. CSF glycine measurement is often crucial to the diagnosis of glycine encephalopathy (GE), low CSF serine concentrations are characteristic of 3-phosphoglycerate dehydrogenase deficiency (3-PGDD) and the presence of sulphocysteine is pathognomonic of sulphite oxidase deficiency (SOD), and a vital clue to molybdenum cofactor deficiency (MCD). Limited information is available in the literature on reference values of amino acids in CSF during infancy and CSF samples from healthy individuals are not easily obtained.

Methods: In order to establish paediatric CSF amino acid reference ranges, we performed a retrospective analysis of all quantitative CSF amino acid data collected in our laboratory over a five-year period. Amino acid analysis was performed using ion-exchange chromatography on a Biochrom-20 amino acid analyser with ninhydrin detection. CSF samples were collected from infants undergoing investigation for unexplained seizures.

Results: About 18 of the 95 samples received were excluded from the reference data-set; one was from a patient in whom a diagnosis of GE was confirmed by enzyme analysis, one was from a patient with CSF sulphocysteine of 19 μmol/L in whom a diagnosis of SOD was confirmed by enzyme analysis; the remaining 16 were clearly bloodstained ( n = 4) or xanthochromic ( n = 12). Frequency of distribution analysis revealed that concentration values for each amino acid demonstrated a right-skewed distribution which was not normalized by log transformation. Data were therefore analysed using non-parametric descriptive statistics and reference ranges were defined by the 2.5th and 97.5th centile limits.

Conclusions: Our reference data were derived from 77 CSF samples taken from 77 infants. Median CSF glycine concentration was 9 μmol/L with a reference range of 3-19 μmol/L. For serine, the median CSF concentration was 52 μmol/L with a reference range of 25-105 μmol/L. Sulphocysteine was not normally present in detectable quantities (<1 μmol/L).

Quantitative acylcarnitine determination by UHPLC-MS/MS--Going beyond tandem MS acylcarnitine "profiles"

Tandem MS "profiling" of acylcarnitines and amino acids was conceived as a first-tier screening method, and its application to expanded newborn screening has been enormously successful. However, unlike amino acid screening (which uses amino acid analysis as its second-tier validation of screening results), acylcarnitine "profiling" also assumed the role of second-tier validation, due to the lack of a generally accepted second-tier acylcarnitine determination method. In this report, we present results from the application of our validated UHPLC-MS/MS second-tier method for the quantification of total carnitine, free carnitine, butyrobetaine, and acylcarnitines to patient samples with known diagnoses: malonic acidemia, short-chain acyl-CoA dehydrogenase deficiency (SCADD) or isobutyryl-CoA dehydrogenase deficiency (IBD), 3-methyl-crotonyl carboxylase deficiency (3-MCC) or ß-ketothiolase deficiency (BKT), and methylmalonic acidemia (MMA). We demonstrate the assay's ability to separate constitutional isomers and diastereomeric acylcarnitines and generate values with a high level of accuracy and precision. These capabilities are unavailable when using tandem MS "profiles". We also show examples of research interest, where separation of acylcarnitine species and accurate and precise acylcarnitine quantification is necessary.

An update on serine deficiency disorders

Serine deficiency disorders are caused by a defect in one of the three synthesising enzymes of the L-serine biosynthesis pathway. Serine deficiency disorders give rise to a neurological phenotype with psychomotor retardation, microcephaly and seizures in newborns and children or progressive polyneuropathy in adult patients. There are three defects that cause serine deficiency of which 3-phosphoglycerate dehydrogenase (3-PGDH) deficiency, the defect affecting the first step in the pathway, has been reported most frequently. The other two disorders in L-serine biosynthesis phosphoserine aminotransferase (PSAT) deficiency and phosphoserine phosphatase (PSP) deficiency have been reported only in a limited number of patients. The biochemical hallmarks of all three disorders are low concentrations of serine in cerebrospinal fluid and plasma. Prompt recognition of affected patients is important, since serine deficiency disorders are treatable causes of neurometabolic disorders. The use of age-related reference values for serine in CSF and plasma can be of great help in establishing a correct diagnosis of serine deficiency, in particular in newborns and young children.

When do we need to perform a diagnostic lumbar puncture for neurometabolic diseases? Positive yield and retrospective analysis from a tertiary center

Neurometabolic diseases diagnosed by cerebrospinal fluid (CSF) examination are GLUT1 deficiency, serine-deficiency syndromes, glycine encephalopathy, cerebral folate deficiency, neonatal vitamin-responsive epileptic encephalopathies, disorders of monoamine metabolism, and y-amino butyric acid (GABA) metabolism. We retrospectively analyzed and compared the demographic, clinical, laboratory, and neuroimaging features of 62 patients in whom CSF examination was performed. Of the 62 patients, 16 (25.8%) had a final diagnosis, including succinic semialdehyde dehydrogenase (SSADH) deficiency (n=4), aromatic amino acid decarboxylase (AADC) deficiency (n=4), L-dopa-responsive dystonia (n=3), glycine encephalopathy (n=2), pyridoxal-phosphate-dependent seizures (n=l), cerebral folate deficiency (n=1), and serine biosynthesi defect (n=1). Parental consanguinity was present in all patients except one Positive yield of a diagnostic lumbar puncture (LP) for the diagnosis of inherited neurotransmitter metabolism disorder was 25.8% overall. Oculogyric crisis (50%), diurnal variation (81.8%) and consanguinity (93.8%) were the only statistically significant variables between patients with and without a specific diagnosis. It is challenging to diagnose neurotransmitter defects, since there is no ideal set of clinical symptoms. In our cohort, consanguinity, diurnal variation and abnormal ocular movements were the most significant findings associated with a diagnosis of a specific neurometabolic disorder based on CSF examination. Early diagnosis is of great importance not only for specific treatment, but also for genetic counseling and prenatal diagnosis.

Multicentre age-related reference intervals for cerebrospinal fluid serine concentrations: implications for the diagnosis and follow-up of serine biosynthesis disorders

The disorders of serine biosynthesis are a group of inborn errors of metabolism characterised by congenital microcephaly, seizures and severe psychomotor retardation. Although these disorders are rare the prompt recognition of serine deficiency is important as these disorders are treatable. The diagnosis is based on decreased concentrations of serine in cerebrospinal fluid (CSF). It has previously been reported that CSF serine concentrations are inversely associated with age. However, accurate age-related reference intervals have not been generated which has contributed to cases not being identified. In a multicentre study involving 9 different laboratories a total of 424 CSF serine results were obtained. Regression based analyses were performed to calculate age-specific reference intervals. Lower reference intervals for subjects aged 1week, 1month, 6months, 1year, 3years and 15years were 35.0, 31.0, 26.0, 24.0, 21.0 and 17.0μmol/L respectively. Assessment of CSF serine concentrations in 11 patients (aged 1day to 13years) previously diagnosed with disorders of serine biosynthesis (serine concentrations ranging from 5 to 18μmol/L) were clearly decreased compared to our age-related reference intervals and would have correctly identified all cases, thus enabling prompt treatment. However, if age had not been taken into consideration a reference interval of 12.6-69.4μmol/L would be obtained for the combined data set and would have resulted in 2 cases being missed. In conclusion, appropriate age-related reference intervals for CSF serine should be used to diagnose patients with inborn errors of serine biosynthesis.

One-methyl group metabolism in non-ketotic hyperglycinaemia: mildly elevated cerebrospinal fluid homocysteine levels

Non-ketotic hyperglycinaemia (NKH) is a rare, severe brain disease caused by deficient glycine cleavage enzyme complex activity resulting in elevated glycine concentrations. Recent experience suggests that factors in addition to glycine kinetics are involved in its pathogenesis. The glycine cleavage reaction through the formation of methylenetetrahydrofolate is an important one-methyl group donor. A deficiency in one-methyl group metabolites, in particular of choline, has been hypothesized in NKH. We investigated metabolites involved in one-methyl group metabolism in plasma and CSF of 8 patients with NKH, and monitored the effect of treatment with choline in one patient. Plasma and CSF choline and phosphatidylcholine concentrations were normal, except for a low plasma choline in the single neonate studied. Choline treatment did not change brain choline content, and was not associated with clinical or radiological improvement. Methionine concentrations and, in one-patient, S-adenosylmethionine and 5-methyltetrahydrofolate concentrations were normal in CSF. Homocysteine concentrations in CSF, however, were slightly but consistently elevated in all four patients examined, but cysteine, cysteinylglycine and glutathione were normal. Serine is important in the transfer of one-methyl groups from mitochondria to cytosol. Serine concentrations were normal in plasma and CSF, but dropped to below normal in CSF in three patients on benzoate treatment. These observations add to our understanding of the complex metabolic disturbances in NKH.

3-Phosphoglycerate dehydrogenase deficiency: an inborn error of serine biosynthesis

Serine concentrations were markedly decreased in the cerebrospinal fluid of two brothers with congenital microcephaly, profound psychomotor retardation, hypertonia, epilepsy, growth retardation, and hypogonadism. The youngest boy also had congenital bilateral cataract. Magnetic resonance imaging of the brain showed evidence of dysmyelination. Plasma serine as well as plasma and cerebrospinal fluid glycine concentrations were also decreased but to a lesser extent. Treatment with oral serine in the youngest patient significantly increased cerebrospinal fluid serine and abolished the convulsions. In fibroblasts of both patients, a decreased activity was demonstrated of 3-phosphoglycerate dehydrogenase, the first step of serine biosynthesis (22% and 13% of the mean control value). This is an unusual disorder as the great majority of aminoacidopathies are catabolic defects. It is a severe but potentially treatable inborn error of metabolism that has not been previously reported in man.

Nonketotic hyperglycinemia in a newborn infant

A neonate with nonketotic hyperglycinemia who experienced apnea, hiccups and tonic-clonic seizures on the first day of life is reported. The physical findings and laboratory tests including arterial blood gases were normal. However, serial blood and CSF amino-acid analyses demonstrated elevated glycine levels. Serum and CSF glycine levels were 1949 mumol/L and 415.5 mumol/L, respectively. (Normal serum level is 104-254 mumol/L and CSF level is 5 +/- 2 mumol/L). The CSF/plasma glycine ratio was 0.11. Oral sodium benzoate and folic acid therapy was initiated. After two weeks of assisted ventilation and clinical improvement, the patient was discharged with a protein-restricted diet.

CT and MR of the brain in disorders of the propionate and methylmalonate metabolism

PURPOSE

To present the CT and MR findings in children with propionic and methylmalonic acidemia.

METHODS

Twenty-three new patients with methylmalonic and 20 with propionic acidemia were examined with CT and/or MR of the brain. In total 52 CT and 55 MR studies were done. Twenty-six previously published cases were also reviewed.

RESULTS

The findings were similar in the two syndromes. During the first month of life the examinations were either normal or showed white matter attenuation. Later during the first year moderate or even severe widening of sulci and fissures was seen, especially in infants with propionic acidemia. During therapy, these changes often resolved, especially in the patients with methylmalonic acidemia. Mild to moderate delay in myelination was also a common finding in both disorders. Basal ganglia changes, predominately in the globus pallidus, were seen in five patients with methylmalonic acidemia and in two children with propionic acidemia; in two patients these changes were transient.

CONCLUSION

Children who have methylmalonic or propionic acidemia, in addition to widening of cerebrospinal fluid spaces and some delay in myelination, also often show symmetric involvement of the basal ganglia.

Atypical nonketotic hyperglycinemia confirmed by assay of the glycine cleavage system in lymphoblasts

A 13-year-old girl with early-onset, mild, slowly progressive mental retardation caused by nonketotic hyperglycinemia is described. The plasma and cerebrospinal fluid glycine concentrations were elevated, but the cerebrospinal fluid/plasma glycine ratio was only mildly elevated. The diagnosis was confirmed by demonstration of a defect in the activity of the glycine cleavage system in cultured lymphoblasts.

Cerebrospinal fluid amino acids, purines and pyrimidines as a tool in the study of metabolic brain diseases

After establishing more extended reference values for amino acids, purines and pyrimidines in cerebrospinal fluid (CSF) in infancy and childhood, we studied 1250 CSF-aliquots from patients who were undergoing a diagnostic lumbar puncture for diverse clinical indications. Our primary aim was to answer the question whether determination of the concentration of amino acids, purines and pyrimidines in CSF is a useful tool in screening for metabolic disorders in children with unexplained mental retardation. In unexplained mental retardation (95 patients) we observed varying abnormalities of CSF. These were reproducible in only 2 patients (a decrease of homocarnosine in combination with two unidentified compounds). Striking abnormalities in pyrimidine content which are limited to CSF are found in argininosuccinic aciduria and uraemia. In uraemia a general decrease in amino acids in CSF and increase of gamma-aminobutyric acid (GABA) was observed. The results obtained indicate that determination of amino acids, purines and pyrimidines in CSF is only of limited value in the diagnosis of unexplained mental retardation.

Inherited disorders of GABA metabolism

Gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in the mammalian central nervous system, is produced from glutamic acid in a reaction catalysed by glutamic acid decarboxylase. The sequential actions of GABA-transaminase (converting GABA to succinic semialdehyde) and succinic semialdehyde dehydrogenase (oxidizing succinic semialdehyde to succinic acid) allow oxidative metabolism of GABA through the tricarboxylic acid cycle. The inherited disorders of GABA metabolism include: (1) pyridoxine-dependent seizures (?glutamic acid decarboxylase deficiency) (> 50 patients); (2) GABA-transaminase deficiency (2 patients/1 family); (3) succinic semialdehyde dehydrogenase deficiency (32 patients/21 families); and (4) homocarnosinosis associated with serum carnosinase deficiency (3 patients/1 family). Homocarnosine is a brain-specific dipeptide of GABA and L-histidine. Of these four defects, definitive enzymatic diagnoses have been made only for GABA-transaminase and succinic semialdehyde dehydrogenase deficiencies. The presumptive mode of inheritance for all disorders is autosomal recessive, and all are associated with central nervous system dysfunction. Only succinic semialdehyde dehydrogenase deficiency manifests organic aciduria, which may account for the higher number of patients identified with this disorder; identification of additional patients with some of the other disorders will require increased request for analysis of cerebrospinal fluid metabolites by paediatricians and neurometabolic specialists.

Glutaric aciduria type 1 an atypical presentation together with some observations upon treatment and the possible cause of cerebral damage

This report describes an infant diagnosed aged twenty-five months as having glutaric aciduria Type 1 (GA 1). Initial presentation was with isolated macrocephaly at four months of age. Severe hypertonia, and dystonia, within 24 hours of minor head injury occurred at nineteen months of age. Serial cranial imaging showed subdural fluid collections, and increasing underlying cerebral atrophy, mainly frontal and temporal. Confirmation of the clinical diagnosis required repeated blood and urine analysis by high performance liquid chromatography and gas chromatography/mass spectrometry; diagnosis was later confirmed enzymologically. Treatment with riboflavin, L-carnitine, vigabatrin and baclofen, produced some symptomatic relief; a low protein diet, nitrazepam and sodium valproate appeared of less obvious use. The rationale for these attempts at treatment is discussed. The possible role of quinolinic acid in the genesis of the fronto temporal and striatal atrophy is discussed and measurement of the quinolinate concentration in cerebrospinal fluid (CSF) of this case and age-related controls is presented.

Neurologic sequelae in transient nonketotic hyperglycinemia of the neonate

We report a neonate with the transient form of nonketotic hyperglycinemia manifested by extreme hypotonia, lethargy, apnea, and myoclonic and generalized convulsions in early neonatal life. Despite normalization of the biochemical values, severe neurologic sequelae were observed. This case suggests that the transient form of nonketotic hyperglycinemia sometimes causes severe brain damage.

Guanidino compound analysis as a complementary diagnostic parameter for hyperargininemia: follow-up of guanidino compound levels during therapy

The aim of this collaborative study was to investigate whether guanidino compound analyses in the biologic fluids can be used as a complementary diagnostic parameter for hyperargininemia. Guanidino compounds were determined in the biologic fluids of all known living hyperargininemic patients using a cation exchange chromatographic system with a fluorescence detection method. The serum arginine, homoarginine, alpha-keto-delta-guanidino-valeric acid, argininic acid, and N-alpha-acetylarginine levels of all the hyperargininemic patients are higher than the normal range. Similar increases were seen for the urinary excretion of alpha-keto-delta-guanidinovaleric acid and argininic acid. Untreated hyperargininemic patients have the highest guanidino compound levels in cerebrospinal fluid. However, even under therapy, the arginine, homoarginine, alpha-keto-delta-guanidinovaleric acid, and argininic acid levels in cerebrospinal fluid are still increased. Protein restriction alone is not sufficient to normalize the hyperargininemia, but protein restriction together with supplementation of essential amino acids with or without sodium benzoate decreases further the arginine levels. However, whereas the argininemia can be normalized, the catabolites of arginine are still increased. We conclude that the urinary amino acid levels may remain normal in hyperargininemia, whereas consistent increases of the guanidino compounds are observed. Thus, guanidino compound analyses can be used as a complementary biochemical diagnostic parameter for hyperargininemia. Although the argininemia can be normalized by therapy, the levels of the catabolites of arginine are still elevated.

Review: Normal and abnormal central nervous system GABA metabolism in childhood

The metabolism and function of central nervous system GABA is briefly reviewed. Hereditary disorders of the GABA metabolism presenting in childhood are discussed with particular emphasis on the recently identified succinic semialdehyde dehydrogenase deficiency and GABA-transaminase deficiency, and on diseases associated with low CSF GABA which await further unravelling. Low CSF GABA concentrations are not always associated with convulsions. A separate section is devoted to the CSF as a tool in the diagnosis of these disorders. Finally, we present a few diagnostic and therapeutic guidelines.

Glycine encephalopathy

4 cases of nonketotic hyperglycinemia (glycine encephalopathy), one with autopsy, are presented and the literature on 61 cases is reviewed. Major clinical signs include early hypotonia, lethargy and erratic and massive myoclonias with respiratory distrubances, starting during the first days of life after a symptom-free interval. Early death is common. Survivors are severely retarded and exhibit various types of seizures including infantile spasms. The EEG pattern consists initially of periodical paroxysmal bursts on an almost flat tracing, evolving later into a hypsarrhythmic pattern. Spongiosis of the myelinated pathways is the main pathological finding. Elevated CSF glycine seems to be the essential determinant of the neurological disturbances and it is, therefore, suggested that the term glycine encephalopathy be used instead of non-ketotic hyperglycinemia. A classification of disorders associated with hyperglycinemia is proposed.

Cerebrospinal fluid glycine in nonketotic hyperglycinemic: effect of treatment with sodium benzoate and a ventricular shunt

In three infants with nonketotic hyperglycinemia, glycine was increased three-to fourfold in plasma, 13- to 28-fold in lumbar spinal fluid, and was higher yet in ventricular fluid. Oral sodium benzoate lowered cerebrospinal fluid (CSF) glycine by greater than 40%, but did not change the abnormal plasma: CSF ratio. An adult control, made hyperglycinemic with oral glycine, had a normal plasma: CSF ratio. Treatment of one patient with sodium benzoate from birth did not prevent mental retardation; the degree of brain stem depression was a function of CSF glycine in another patient. The persistance of glycine elevation in CSF, although therapy maintained normal concentration in plasma, appears to be caused by overproduction in brain and limitation of the high-capacity lumbar spinal reabsorptive mechanism. Treatment through lowering of CNS glycine by use of a ventricular shunt was explored.

Hyperargininemia

A 7 1/2-year-old boy had progressive psychomotor retardation, behavior disturbance, and spasticity, and had growth arrest from age three. Plasma arginine on a self-selected protein-poor diet was increased (4.05 mg/dl; nl 0.4 to 2.6), whereas urinary amino acid excretion was normal. Red blood cell arginase was less than 1% of normal in the patient and was half normal in both parents, in two normal siblings, and in his paternal grandfather. Three hours after a meal providing 2 gm protein/kg body weight, the plasma arginine value rose to 13.2 mg/dl, dibasic aminoaciduria was seen clearly for the only time, but blood ammonia concentration remained normal. We conclude that arginase deficiency in the red blood cells and probably in the liver is inherited in an autosomal recessive manner and is responsible for the clinical syndrome in this patient.

Citrullinaemia with rapidly fatal neonatal course

An infant with a deficiency of argininosuccinate synthetase in liver and brain developed rapidly increasing apathy, respiratory insufficiency, and convulsions from the fourth day of life, and died on the seventh day. There was a profound derangement of amino acid concentrations in blood, CSF, and urine, with very high citrulline levels. This patient differs from other cases reported previously, both in her fulminant and fatal course in the neonatal period and in the greater biochemical disturbance.