The paradox of hyperdopaminuria in aromatic L-amino Acid deficiency explained

The Intricacies of Renal Phosphate Reabsorption-An Overview

To maintain an optimal body content of phosphorus throughout postnatal life, variable phosphate absorption from food must be finely matched with urinary excretion. This amazing feat is accomplished through synchronised phosphate transport by myriads of ciliated cells lining the renal proximal tubules. These respond in real time to changes in phosphate and composition of the renal filtrate and to hormonal instructions. How they do this has stimulated decades of research. New analytical techniques, coupled with incredible advances in computer technology, have opened new avenues for investigation at a sub-cellular level. There has been a surge of research into different aspects of the process. These have verified long-held beliefs and are also dramatically extending our vision of the intense, integrated, intracellular activity which mediates phosphate absorption. Already, some have indicated new approaches for pharmacological intervention to regulate phosphate in common conditions, including chronic renal failure and osteoporosis, as well as rare inherited biochemical disorders. It is a rapidly evolving field. The aim here is to provide an overview of our current knowledge, to show where it is leading, and where there are uncertainties. Hopefully, this will raise questions and stimulate new ideas for further research.

Diagnosis of Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency via Epilepsy Gene Panel Screening in a Patient with Atypical Presentation

We describe an atypical presentation of a girl with aromatic L-amino acid decarboxylase (AADC) deficiency identified via a genetic testing program for children with epilepsy. At 21 months of age, she presented with poor head control, diffuse hypotonia, poor fixation, developmental delay, and dysphagia. She was lost to follow-up, then presented back at 3 years of age with staring spells and brief episodes of upward eye deviation. The diagnosis of unprovoked epilepsy allowed her to be included in a genetic testing program, which identified two heterozygous variants in the dopa decarboxylase (DCC) gene. Based on the genetic testing, plasma AADC enzyme activity and plasma 3-O-methyldopa results, a diagnosis of AADC deficiency was made when she was 4 years and 2 months of age. This case report shows that AADC deficiency can be the underlying diagnosis in patients with suspected epilepsy.

Blood, urine and cerebrospinal fluid analysis in TH and AADC deficiency and the effect of treatment

Background

Aromatic L-amino acid decarboxylase (AADC) deficiency and tyrosine hydroxylase (TH) deficiency are rare inherited disorders of monoamine neurotransmitter synthesis which are typically diagnosed using cerebrospinal fluid examination of monoamine neurotransmitter metabolites. Until now, it has not been systematically studied whether analysis of monamine neurotransmitter metabolites in blood or urine has diagnostic value as compared to cerebrospinal fluid examination, or whether monoamine neurotransmitter metabolites in these peripheral body fluids is useful to monitor treatment efficacy.

Methods

Assessment, both by literature review and retrospective analysis of our local university hospital database, of monoamine neurotransmitter metabolites in urine, blood and cerebrospinal fluid, and serum prolactin levels, before and during treatment in patients with AADC and TH deficiency.

Results

In AADC deficiency, 3-O-methyldopa in serum or dried blood spots was reported in 34 patients and found to be (strongly) increased in all, serotonin in serum was decreased in 7/7 patients. Serum prolactin was increased in 34/37 and normal in 3 untreated patients. In urine, dopamine was normal or increased in 21/24 patients, 5-hydroxyindoleacetic acid was decreased in 9/10 patients, and vanillactic acid was increased in 19/20 patients. No significant changes were seen in monoamine neurotransmitter metabolites after medical treatment, except for an increase of homovanillic acid in urine and cerebrospinal fluid after levodopa therapy, sometimes even in absence of a clinical response. After gene therapy, cerebrospinal fluid homovanillic acid increased in most patients (8/12), but 5-hydroxyindoleacetic acid remained unchanged in 9/12 patients.

In TH deficiency, serum prolactin was increased in 12/14 and normal in the remaining untreated patients. Urinary dopamine was decreased in 2/8 patients and normal in 6. Homovanillic acid concentrations in cerebrospinal fluid increased upon levodopa treatment, even in the absence of a clear treatment response.

Conclusions

This study confirms that cerebrospinal fluid is the most informative body fluid to measure monoamine neurotransmitter metabolites when AADC or TH deficiency is suspected, and that routine follow-up of cerebrospinal fluid measurements to estimate treatment response is not needed. 3-O-methyldopa in dried blood spots and vanillactic acid in urine are promising peripheral biomarkers for diagnosis of AADC deficiency. However, in many patients with TH or AADC deficiency dopamine in urine is normal or increased thereby not reflecting the metabolic block. The value of serum prolactin for follow-up of AADC and TH deficiency should be further studied.

Dopamine Receptors and the Kidney: An Overview of Health- and Pharmacological-Targeted Implications

The dopaminergic system can adapt to the different physiological or pathological situations to which the kidneys are subjected throughout life, maintaining homeostasis of natriuresis, extracellular volume, and blood pressure levels. The role of renal dopamine receptor dysfunction is clearly established in the pathogenesis of essential hypertension. Its associations with other pathological states such as insulin resistance and redox balance have also been associated with dysfunction of the dopaminergic system. The different dopamine receptors (D1-D5) show a protective effect against hypertension and kidney disorders. It is essential to take into account the various interactions of the dopaminergic system with other elements, such as adrenergic receptors. The approach to therapeutic strategies for essential hypertension must go through the blocking of those elements that lead to renal vasoconstriction or the restoration of the normal functioning of dopamine receptors. D1-like receptors are fundamental in this role, and new therapeutic efforts should be directed to the restoration of their functioning in many patients. More studies will be needed to allow the development of drugs that can be targeted to renal dopamine receptors in the treatment of hypertension.

Genipap (Genipa americana L.) juice intake biomarkers after medium-term consumption

Genipap (Genipa americana L.) is an exotic fruit largely consumed and well known, in Amazonian pharmacopeia, to treat anemia, measles and uterine cancer. It is also used as a diuretic, digestive, healing, laxative and antiseptic. The aim of this study was to apply an untargeted metabolomics strategy to determine biomarkers of food intake after short-term consumption of genipap juice. Sixteen healthy adult men were administered jenipap juice (250 mL) twice a day for three weeks. Before and after the three weeks of consumption. the subjects drank a control drink, and they consumed a standard diet. Urine was collected after 0-6 h, 6-12 h and 12-24 h. An ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS)-based metabolomics approach was applied to analyze the urine samples. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were performed to highlight experimental differences between groups. The value of the area under the curve (AUC) of the receiver operator characteristic (ROC) curve validated the identified biomarkers. Thirty-one statistically affected urinary metabolites were putatively identified and were mainly related to iridoids family, medium-chain fatty acids, and polyphenols. Also a group of urinary markers including dihydrocaffeic acid (DHCA), 1-(4-hydroxyphenyl)-1,2-propanediol and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid were established as biomarkers of genipap consumption. Our findings have established a comprehensive panel of changes in the urinary metabolome and provided information to monitor endogenous alterations that are linked to genipap juice intake. These data should be used in further studies to understand the health implications of genipap juice consumption.

Prevalence of Aromatic l-Amino Acid Decarboxylase Deficiency in At-Risk Populations

BACKGROUND

Aromatic l-amino acid decarboxylase (AADC) deficiency is an autosomal recessive metabolic disorder that results from disease-causing pathogenic variants of the dopa decarboxylase (DDC) gene. Loss of dopamine and serotonin production in the brain from infancy prevents achievement of motor developmental milestones.

METHODS

We retrospectively evaluated data obtained from requests to Medical Neurogenetics Laboratories for analyses of neurotransmitter metabolites in the cerebrospinal fluid, AADC enzyme activity in plasma, and/or Sanger sequencing of the DDC gene. Our primary objective was to estimate the prevalence of AADC deficiency in an at-risk population.

RESULTS

Approximately 20,000 cerebrospinal fluid samples were received with a request for neurotransmitter metabolite analysis in the eight-year study period; 22 samples tested positive for AADC deficiency based on decreased concentrations of 5-hydroxyindoleacetic acid and homovanillic acid, and increased 3-O-methyldopa, establishing an estimated prevalence of approximately 0.112%, or 1:900. Of the 81 requests received for plasma AADC enzyme analysis, 25 samples had very low plasma AADC activity consistent with AADC deficiency, resulting in identification of nine additional cases. A total of five additional patients were identified by Sanger sequencing as the primary request leading to the diagnosis of AADC deficiency.

CONCLUSIONS

Overall, these analyses identified 36 new cases of AADC deficiency. Sequencing findings showed substantial diversity with identification of 26 different DDC gene variants; five had not previously been associated with AADC deficiency. The results of the present study align with the emerging literature and understanding of the epidemiology and genetics of AADC deficiency.

A new common functional coding variant at the DDC gene change renal enzyme activity and modify renal dopamine function

The intra-renal dopamine (DA) system is highly expressed in the proximal tubule and contributes to Na+ and blood pressure homeostasis, as well as to the development of nephropathy. In the kidney, the enzyme DOPA Decarboxylase (DDC) originating from the circulation. We used a twin/family study design, followed by polymorphism association analysis at DDC locus to elucidate heritable influences on renal DA production. Dense single nucleotide polymorphism (SNP) genotyping across the DDC locus on chromosome 7p12 was analyzed by re-sequencing guided by trait-associated genetic markers to discover the responsible genetic variation. We also characterized kinetics of the expressed DDC mutant enzyme. Systematic polymorphism screening across the 15-Exon DDC locus revealed a single coding variant in Exon-14 that was associated with DA excretion and multiple other renal traits indicating pleiotropy. When expressed and characterized in eukaryotic cells, the 462Gln variant displayed lower Vmax (maximal rate of product formation by an enzyme) (21.3 versus 44.9 nmol/min/mg) and lower Km (substrate concentration at which half-maximal product formation is achieved by an enzyme.)(36.2 versus 46.8 μM) than the wild-type (Arg462) allele. The highly heritable DA excretion trait is substantially influenced by a previously uncharacterized common coding variant (Arg462Gln) at the DDC gene that affects multiple renal tubular and glomerular traits, and predicts accelerated functional decline in chronic kidney disease.

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.

Report of two never treated adult sisters with aromatic L-amino Acid decarboxylase deficiency: a portrait of the natural history of the disease or an expanding phenotype?

Two sisters were diagnosed in their adulthood with aromatic L-amino acid decarboxylase (AADC) deficiency (OMIM#608643). They experienced early myasthenia-like manifestations, myoclonic jerks, oculogyric crises, tremors, and developmental delay during childhood; clinical stabilization afterwards; and spontaneous improvement during adolescence and young adulthood. Two novel pathogenic mutations on DDC gene [p.Tyr37Thrfs*5 (c.105delC) and p.F237S (c.710 T>C)] were associated with undetectable enzyme activity in plasma and only a mild reduction of biogenic amines in cerebrospinal fluid (CSF). The increase of both 3-O-methyldopa and 5-hydroxytryptophan on CSF was the most relevant biochemical alteration denoting AADC defect in these subjects. Transdermal rotigotine remarkably improved their gross motor functions and the asthenic status they complained. The present cases broaden the phenotypic spectrum of AADC deficiency and suggest that (1) AADC defect is not a progressive neurological disease and behaves rather as a neurodevelopmental disorder that improves during the second decade of life; (2) treatment-naïve adults can still respond well to neurotransmitter therapy; and (3) the possibility of a mild presentation of AADC deficiency should be considered when examining young adults with asthenic and parkinsonian symptoms.