The clinical relevance of novel biomarkers as outcome parameter in adults with phenylketonuria.

Recent studies in PKU patients identified alternative biomarkers in blood using untargeted metabolomics. To test the added clinical value of these novel biomarkers, targeted metabolomics of 11 PKU biomarkers (phenylalanine, glutamyl-phenylalanine, glutamyl-glutamyl-phenylalanine, N-lactoyl-phenylalanine, N-acetyl-phenylalanine, the dipeptides phenylalanyl-phenylalanine and phenylalanyl-leucine, phenylalanine-hexose conjugate, phenyllactate, phenylpyruvate, and phenylacetate) was performed in stored serum samples of the well-defined PKU patient-COBESO cohort and a healthy control group. Serum samples of 35 PKU adults and 20 healthy age- and sex-matched controls were analyzed using ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry. Group differences were tested using the Mann-Whitney U test. Multiple linear regression analyses were performed with these biomarkers as predictors of (neuro-)cognitive functions working memory, sustained attention, inhibitory control, and mental health. Compared to healthy controls, phenylalanine, glutamyl-phenylalanine, N-lactoyl-phenylalanine, N-acetyl-phenylalanine, phenylalanine-hexose conjugate, phenyllactate, phenylpyruvate, and phenylacetate were significant elevated in PKU adults (p < 0.001). The remaining three were below limit of detection in PKU and controls. Both phenylalanine and N-lactoyl-phenylalanine were associated with DSM-VI Attention deficit/hyperactivity (R2 = 0.195, p = 0.039 and R2 = 0.335, p = 0.002, respectively) of the ASR questionnaire. In addition, N-lactoyl-phenylalanine showed significant associations with ASR DSM-VI avoidant personality (R2 = 0.265, p = 0.010), internalizing (R2 = 0.192, p = 0.046) and externalizing problems (R2 = 0.217, p = 0.029) of the ASR questionnaire and multiple aspects of the MS2D and FI tests, reflecting working memory with R2 between 0.178 (p = 0.048) and 0.204 (p = 0.033). Even though the strength of the models was not considered strong, N-lactoyl-phenylalanine outperformed phenylalanine in its association with working memory and mental health outcomes.

Cerebrotendinous xanthomatosis without neurological involvement.

BACKGROUND: Cerebrotendinous xanthomatosis (CTX) is an autosomal recessively inherited inborn error of metabolism. Neurological symptoms are considered to be a clinical hallmark of untreated adult patients. We describe a 'milder CTX phenotype', without neurological involvement. METHODS: We performed a retrospective patient file study in 79 genetically confirmed Dutch patients with CTX (55 patients aged ≥ 21 years) to study the clinical heterogeneity of CTX. We studied the frequency of adult patients with CTX without neurological involvement at diagnosis, in our Dutch cohort, and included a family from South Africa and patients from Italy, USA, Chile and Asia from the literature. RESULTS: In total, we describe 19 adult patients with CTX from 16 independent families, without neurological symptoms at diagnosis. A relatively small percentage (21%, n = 4) had a history of cataract. The majority, 84% (n = 16), presented with tendon xanthomas as the sole or predominant feature. The majority of patients showed increased plasma cholesterol levels. No correlation was found between this 'milder phenotype', the cholestanol levels and the CYP27A1 genotype. In addition, we describe three novel mutations in the CYP27A1 gene. CONCLUSIONS: This study shows the clinical heterogeneity of CTX, highlighting the existence of a 'milder phenotype', that is without neurological involvement at diagnosis. Adult patients with CTX may present with tendon xanthomas as the sole or predominant feature, mimicking familial hypercholesterolemia. It is important to realize that the absence of neurological symptoms does not rule out the development of future neurological symptoms. As CTX is a treatable disorder, early diagnosis and initiation of treatment when additional clinical signs occur is therefore essential.

Functional disruption of pyrimidine nucleoside transporter CNT1 results in a novel inborn error of metabolism with high excretion of uridine and cytidine.

Genetic defects in the pyrimidine nucleoside transporters of the CNT transporter family have not yet been reported. Metabolic investigations in a patient with infantile afebrile tonic-clonic seizures revealed increased urinary uridine and cytidine excretion. Segregation of this metabolic trait in the family showed the same biochemical phenotype in a healthy older brother of the index. Whole exome sequencing revealed biallelic mutations in SLC28A1 encoding the pyrimidine nucleoside transporter CNT1 in the index and his brother. Both parents and unaffected sibs showed the variant in heterozygous state. The transporter is expressed in the kidneys. Compelling evidence is available for the disrupting effect of the mutation on the transport function thus explaining the increased excretion of the pyrimidine nucleosides. The exome analysis also revealed a pathogenic mutation in PRRT2 in the index, explaining the epilepsy phenotype in infancy. At present, both the index (10 years) and his older brother are asymptomatic. Mutations in SLC28A1 cause a novel inborn error of metabolism that can be explained by the disrupted activity of the pyrimidine nucleoside transporter CNT1. This is the first report describing a defect in the family of CNT concentrative pyrimidine nucleoside transporter proteins encoded by the SLC28 gene family. In all likelihood, the epilepsy phenotype in the index is unrelated to the SLC28A1 defect, as this can be fully explained by the pathogenic PRRT2 variant. Clinical data on more patients are required to prove whether pathogenic mutations in SLC28A1 have any clinical consequences or are to be considered a benign metabolic phenotype.

A homozygous DPM3 mutation in a patient with alpha-dystroglycan-related limb girdle muscular dystrophy.

Defects of O-linked glycosylation of alpha-dystroglycan cause a wide spectrum of muscular dystrophies ranging from severe congenital muscular dystrophy associated with abnormal brain and eye development to mild limb girdle muscular dystrophy. We report a female patient who developed isolated pelvic girdle muscle weakness and wasting, which became symptomatic at age 42. Exome sequencing uncovered a homozygous c.131T > G (p.Leu44Pro) substitution in DPM3, encoding dolichol-P-mannose (DPM) synthase subunit 3, leading to a 50% reduction of enzymatic activity. Decreased availability of DPM as an essential donor substrate for protein O-mannosyltransferase (POMT) 1 and 2 explains defective skeletal muscle alpha-dystroglycan O-glycosylation. Our findings show that DPM3 mutations may lead to an isolated and mild limb girdle muscular dystrophy phenotype without cardiomyopathy.

Detection of Staphylococcus aureus in cystic fibrosis patients using breath VOC profiles.

Staphylococcus aureus (S. aureus) is a common bacterium infecting children with cystic fibrosis (CF). Since current detection methods are difficult to perform in children, there is need for an alternative. This proof of concept study investigates whether breath profiles can discriminate between S. aureus infected and non-infected CF patients based on volatile organic compounds (VOCs). We collected exhaled breath of CF patients with and without S. aureus airways infections in which VOCs were identified using gas chromatography-mass spectrometry. We classified these VOC profiles with sparse partial least squares discriminant analysis. Multivariate breath VOC profiles discriminated infected from non-infected CF patients with high sensitivity (100%) and specificity (80%). We identified the nine compounds most important for this discrimination. We successfully detected S. aureus infection in CF patients, using breath VOC profiles. Nine highlighted compounds can be used as a focus point in further biomarker identification research. The results show considerable potential for non-invasive diagnosis of airway infections.

Identification of Pseudomonas aeruginosa and Aspergillus fumigatus mono- and co-cultures based on volatile biomarker combinations.

Volatile organic compound (VOC) analysis in exhaled breath is proposed as a non-invasive method to detect respiratory infections in cystic fibrosis patients. Since polymicrobial infections are common, we assessed whether we could distinguish Pseudomonas aeruginosa and Aspergillus fumigatus mono- and co-cultures using the VOC emissions. We took headspace samples of P. aeruginosa, A. fumigatus and co-cultures at 16, 24 and 48 h after inoculation, in which VOCs were identified by thermal desorption combined with gas chromatography - mass spectrometry. Using multivariate analysis by Partial Least Squares Discriminant Analysis we found distinct VOC biomarker combinations for mono- and co-cultures at each sampling time point, showing that there is an interaction between the two pathogens, with P. aeruginosa dominating the co-culture at 48 h. Furthermore, time-independent VOC biomarker combinations were also obtained to predict correct identification of P. aeruginosa and A. fumigatus in mono-culture and in co-culture. This study shows that the VOC combinations in P. aeruginosa and A. fumigatus co-microbial environment are different from those released by these pathogens in mono-culture. Using advanced data analysis techniques such as PLS-DA, time-independent pathogen specific biomarker combinations can be generated that may help to detect mixed respiratory infections in exhaled breath of cystic fibrosis patients.

Regularized MANOVA (rMANOVA) in untargeted metabolomics.

Many advanced metabolomics experiments currently lead to data where a large number of response variables were measured while one or several factors were changed. Often the number of response variables vastly exceeds the sample size and well-established techniques such as multivariate analysis of variance (MANOVA) cannot be used to analyze the data. ANOVA simultaneous component analysis (ASCA) is an alternative to MANOVA for analysis of metabolomics data from an experimental design. In this paper, we show that ASCA assumes that none of the metabolites are correlated and that they all have the same variance. Because of these assumptions, ASCA may relate the wrong variables to a factor. This reduces the power of the method and hampers interpretation. We propose an improved model that is essentially a weighted average of the ASCA and MANOVA models. The optimal weight is determined in a data-driven fashion. Compared to ASCA, this method assumes that variables can correlate, leading to a more realistic view of the data. Compared to MANOVA, the model is also applicable when the number of samples is (much) smaller than the number of variables. These advantages are demonstrated by means of simulated and real data examples. The source code of the method is available from the first author upon request, and at the following github repository: https://github.com/JasperE/regularized-MANOVA.

Hypercholesterolaemia and hepatosplenomegaly: two manifestations of cholesteryl ester storage disease.

Cholesteryl ester storage disease (CESD) is a rare autosomal recessive disease caused by mutations in LIPA. Here we describe two different clinical presentations of this disease: one case with a clear phenotype of familial hypercholesterolaemia and one case with hepatosplenomegaly from childhood onwards. These two cases exemplify the diversity of clinical phenotypes of patients with CESD. Knowledge on the phenotypic variability of the disease is of clinical relevance in light of enzyme replacement therapy (sebelipase alpha) for patients with mutations in LIPA, which is currently under development.

Genotype-specific differences in the tumor metabolite profile of pheochromocytoma and paraganglioma using untargeted and targeted metabolomics.

CONTEXT AND OBJECTIVE: Pheochromocytomas and paragangliomas (PGLs) are neuroendocrine tumors of sympathetic or parasympathetic paraganglia. Nearly 40% of PGLs are caused by germline mutations. The present study investigated the effect of genetic alterations on metabolic networks in PGLs. DESIGN: Homogenates of 32 sporadic PGLs and 48 PGLs from patients with mutations in SDHB, SDHD, SDHAF-2, VHL, RET, and NF-1 were subjected to proton ((1)H) nuclear magnetic resonance (NMR) spectroscopy at 500 MHz for untargeted and HPLC tandem mass spectrometry for targeted metabolite profiling. RESULTS: (1)H NMR spectroscopy identified 28 metabolites in PGLs of which 12 showed genotype-specific differences. Part of these results published earlier reported low complex II activity (P < .0001) and low ATP/ADP/AMP content (P < .001) in SDH-related PGLs compared with sporadics and PGLs of other genotypes. Extending these results, low levels of N-acetylaspartic acid (NAA; P < .05) in SDH tumors and creatine (P < .05) in VHL tumors were observed compared with sporadics and other genotypes. Positive correlation was observed between NAA and ATP/ADP/AMP content (P < .001) and NAA and complex II activity (P < .0001) of PGLs. Targeted purine analysis in PGLs showed low adenine in cluster 1 compared with cluster 2 tumors (SDH P < .0001; VHL P < .05) whereas lower levels (P < .05) of guanosine and hypoxanthine were observed in RET tumors compared with SDH tumors. Principal component analysis (PCA) of metabolites could distinguish PGLs of different genotypes. CONCLUSIONS: The present study gives a comprehensive picture of alterations in energy metabolism in SDH- and VHL-related PGLs and establishes the interrelationship of energy metabolism and amino acid and purine metabolism in PGLs.

Early life adversity and serotonin transporter gene variation interact at the level of the adrenal gland to affect the adult hypothalamo-pituitary-adrenal axis.

The short allelic variant of the serotonin transporter (5-HTT) promoter-linked polymorphic region (5-HTTLPR) has been associated with the etiology of major depression by interaction with early life stress (ELS). Furthermore, 5-HTTLPR has been associated with abnormal functioning of the stress-responsive hypothalamo-pituitary-adrenal (HPA) axis. Here, we examined if, and at what level, the HPA-axis is affected in an animal model for ELS × 5-HTTLPR interactions. Heterozygous and homozygous 5-HTT knockout rats and their wild-type littermates were exposed daily at postnatal days 2-14 to 3 h of maternal separation. When grown to adulthood, plasma levels of adrenocorticotropic hormone (ACTH), and the major rat glucocorticoid, corticosterone (CORT), were measured. Furthermore, the gene expression of key HPA-axis players at the level of the hypothalamus, pituitary and adrenal glands was assessed. No 5-HTT genotype × ELS interaction effects on gene expression were observed at the level of the hypothalamus or pituitary. However, we found significant 5-HTT genotype × ELS interaction effects for plasma CORT levels and adrenal mRNA levels of the ACTH receptor, such that 5-HTT deficiency was associated under control conditions with increased, but after ELS with decreased basal HPA-axis activity. With the use of an in vitro adrenal assay, naïve 5-HTT knockout rats were furthermore shown to display increased adrenal ACTH sensitivity. Therefore, we conclude that basal HPA-axis activity is affected by the interaction of 5-HTT genotype and ELS, and is programmed, within the axis itself, predominantly at the level of the adrenal gland. This study therefore emphasizes the importance of the adrenal gland for HPA-related psychiatric disorders.

Alpha-fetoprotein, a fascinating protein and biomarker in neurology.

Alpha-fetoprotein (AFP) is present in fetal serum in concentrations up to 5,000,000 µg/l. After birth, AFP gene expression is turned down with a subsequent fall of the serum concentrations of this albumin-like protein to 'adult values' of circa 0.5-15 µg/l from the age of 2 years onwards. Irrespective of its assumed important functions, individuals with AFP deficiency appear fully healthy. The other way around, the presence of AFP in the circulation after the first years of life doesn't seem to harm, since individuals with 'hereditary persistence of AFP' are also without clinical abnormalities. During pregnancy, AFP (in maternal serum) has long been recognized as a marker for congenital anomalies of the fetus. Equally well known is AFP as biomarker for hepatocellular carcinoma and some other malignancies. There are at least four neurodegenerative disorders, all inherited as autosomal recessive traits and characterized by the presence of cerebellar ataxia, abnormal ocular movements, and neuropathy, for which an elevated concentration of serum AFP is an important diagnostic biomarker. The availability of a reliable biomarker is not only important during screening or diagnostic processes, but is also relevant for objective follow-up during (future) therapeutic interventions.

Thrombotic complications in patients with PMM2-CDG.

Many proteins regulating coagulation, including factor IX, factor XI, Antithrombin-III, Protein C and Protein S are deficient or decreased in activity in congenital disorders of glycosylation (CDG). Because of the imbalance of coagulation and anticoagulation factors, some patients develop acute vascular events, such as thrombosis. Identifying patients with increased risk for thrombotic events could prevent serious complications and even mortality. We performed a systematic review on patients diagnosed with the most common CDG form; PMM2-CDG, reported between 1990 and 2012 in medical literature. We also evaluated our PMM2-CDG patient-cohort of 15 patients. In total, based on the availability of comprehensive clinical descriptions, 100 patients were included in the study. Patients with and without thrombotic events were compared based on the alterations of the following glycosylated coagulation and anticoagulation factors: Antithrombin-III, Protein C, Protein S, factors IX and XI. We also assessed the global hemostasis, family history and provoking events. In the group of 100 PMM2-CDG patients 14 had suffered a venous or arterial thrombotic event. Low activity of several anticoagulation factors correlated with thrombotic events. Relatively high factor IX and XI activities were not associated with thrombosis. Prolonged PT and aPTT did not seem to protect against thrombosis in patients. Surgical procedures were frequently associated with thrombotic events. Based on the association of thrombosis and surgery in PMM2-CDG we advise to avoid elective surgical procedures in PMM2-CDG patients. Easily preventable risk factors like immobility should be treated with regular physiotherapy. We suggest a yearly follow-up for Antithrombin-III and Protein C levels and parent education for early thrombotic signs in CDG.

Acid sphingomyelinase (Asm) deficiency patients in The Netherlands and Belgium: disease spectrum and natural course in attenuated patients.

Niemann-Pick disease (NPD) is a neurovisceral lysosomal storage disorder caused by acid sphingomyelinase (ASM) deficiency, which can be categorized as either Niemann-Pick disease type A [NPD-A], with progressive neurological disease and death in early childhood, or as Niemann-Pick disease type B [NPD-B], with a more variable spectrum of manifestations. Enzyme replacement therapy (ERT) with recombinant sphingomyelinase is currently studied as potential treatment for NPD-B patients. The objective of this study is to characterize the clinical features of patients with ASM deficiency in the Netherlands and Belgium with focus on the natural disease course of NPD-B patients. Prospective and retrospective data on ASM deficient patients were collected in The Netherlands and part of Belgium. Patients with NPD-B that could be followed prospectively were evaluated every 6-12 months for pulmonary function tests, 6 minute walk test (6 MWT), imaging (bone marrow infiltration measured by QCSI, organ volumes by MRI and CT scan of the lungs) and biochemical markers. Twenty-five patients with ASM deficiency were identified (13 males, 12 females, median age 13years, range 1-59 years). Nine patients had died at the time of the study, including four NPD-A patients at the age of 1,1, 2, 3 and five NPDB patents at the age of 5, 6, 43, 56 and 60 years. There was a high prevalence of homozygosity and compound heterozygosity for the common p.Arg608del mutation in 43% and 19% of NPD-B patients, respectively. In NPD-B patients, thrombocytopenia was present in most, while anemia and leucopenia were less common (33% and 6 % respectively). HDL cholesterol was reduced in most patients. Pulmonary disease was severe in several patients. Follow-up up to 11 years revealed a gradual decrease in platelet count. Detailed investigations in 6 NPD-B patients with follow-up in 4 patients revealed remarkable stable disease parameters up to 6 years, with some decline in pulmonary function and 6 MWT. Bone marrow fat fractions were decreased, indicating the presence of storage macrophages. Lung involvement was not related to the extent of visceromegaly, cytopenia or bone marrow involvement. In conclusion, in NPD-B patients pulmonary disease is the most debilitating feature. Disease manifestations are mostly stable in attenuated patients. Bone marrow infiltration is a less prominent feature of the disease.

Glycosylation defects underlying fetal alcohol spectrum disorder: a novel pathogenetic model. "When the wine goes in, strange things come out" - S.T. Coleridge, The Piccolomini.

Fetal alcohol spectrum disorder (FASD) is an umbrella term used to describe the craniofacial dysmorphic features, malformations, and disturbances in growth, neurodevelopment and behavior occurring in individuals prenatally exposed to alcohol. Fetal alcohol syndrome (FAS) represents the severe end of this spectrum. Many pathophysiological mechanisms have hitherto been proposed to account for the disrupted growth and morphogenesis seen in FAS. These include impaired cholesterol-modification of the Sonic hedgehog morphogen, retinoic acid deficiency, lipoperoxidative damage due to alcohol-induced reactive oxygen species combined with reduced antioxidant defences, and malfunctioning cell adhesion molecules. In this report, we propose a completely novel concept regarding the pathogenesis of FAS. Based on our observation that transferrin isoelectric focusing (TIEF) - the most widely used screening tool for congenital disorders of glycosylation (CDG) - was transiently abnormal in a newborn with FAS and a confirmed maternal history of gestational alcohol abuse, we came to believe that FAS exemplifies a congenital disorder of glycosylation secondary to alcohol-inflicted disruption of (N-linked) protein glycosylation. Various pieces of evidence were found in the literature to substantiate this hypothesis. This observation implies, among others, that one might need to consider the possibility of maternal alcohol consumption in newborns with transient glycosylation abnormalities. We also present an integrated pathophysiological model of FAS, which incorporates all existing theories mentioned above as well as our novel concept. This model highlights the pivotal role of disrupted isoprenoid metabolism in the origination of FAS.

Clinical and diagnostic approach in unsolved CDG patients with a type 2 transferrin pattern.

Dysmorphic features, multisystem disease, and central nervous system involvement are common symptoms in congenital disorders of glycosylation, including several recently discovered Golgi-related glycosylation defects. In search for discriminative features, we assessed eleven children suspected with a Golgi-related inborn error of glycosylation. We evaluated all genetically unsolved patients, diagnosed with a type 2 transferrin isofocusing pattern in the period of 1999-2009. By combining biochemical results with characteristic clinical symptoms, we used a diagnostic flow chart to approach the underlying defect in patients with congenital disorders of glycosylation-IIx. According to specific symptoms and laboratory results, we initiated additional, targeted biochemical and genetic studies. We found a distinctive spectrum of congenital disorders of glycosylation type 2-associated anomalies including sudden hearing loss, brain malformations, wrinkled skin, and epilepsy in combination with skeletal dysplasia, dilated cardiomyopathy, sudden cardiac arrest, abnormal copper and iron metabolism, and endocrine abnormalities in our patients. One patient with severe cortical malformations and mild skin abnormalities was diagnosed with a known genetic syndrome, due to an ATP6V0A2 defect. Here, we present unique congenital disorders of glycosylation type 2-associated anomalies, including both ATPase-related and unrelated cutis laxa and sensorineural hearing loss, a recently recognized symptom of congenital disorders of glycosylation. Based on our findings, we recommend clinicians to consider congenital disorders of glycosylation in patients with cardiac rhythm disorders, spondylodysplasia and biochemical abnormalities of the copper and iron metabolism even in absence of intellectual disability.

Clinical imaging and neuropathological correlations in an unusual case of cerebrotendinous xanthomatosis.

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive lipid storage disorder due to a deficiency of the mitochondrial enzyme sterol 27-hydroxylase (CYP 27) with reduced or no chenodeoxycholic synthesis. This deficiency leads to an accumulation of cholestanol in different sites such as the eye lens, central nervous system or tendons. We report a 64-year-old female patient with a progressive gait disorder associated with cognitive decline since the age of 59. The patient had no mental retardation, cataract or chronic diarrhea. Her family reported increasing behavioral modifications 10 years previously. Clinical examination revealed a spastic paraplegia and bilateral xanthomas on the Achilles tendons. Cerebral magnetic resonance imaging (MRI) revealed diffuse hyperintense T2 abnormalities in the pyramidal tracts from the internal capsules to the cerebral peduncles also Technetium-99m-ECD brain SPECT showed a severe cerebellar hypoperfusion. Serum cholestanol analysis was 7 µmol/l (N). After 2 years, she was bedridden and died of aspiration pneumonia. The neuropathological study confirmed the CTX diagnosis and the sequencing analysis revealed that she was compound heterozygous for two mutations in the CYP27A1 gene: 1435 C > T (exon 7) on one allele and a new mutation, 1017 G > C (exon 5) on the other. The interest of the present case is to report neuropathology findings strongly correlated with the MRI and SPECT abnormalities.

3-Methylglutaconic aciduria type I redefined: a syndrome with late-onset leukoencephalopathy.

OBJECTIVE: 3-Methylglutaconic aciduria type I is a rare inborn error of leucine catabolism. It is thought to present in childhood with nonspecific symptoms; it was even speculated to be a nondisease. The natural course of disease is unknown. METHODS: This is a study on 10 patients with 3-methylglutaconic aciduria type I. We present the clinical, neuroradiologic, biochemical, and genetic details on 2 new adult-onset patients and follow-up data on 2 patients from the literature. RESULTS: Two unrelated patients with the characteristic biochemical findings of 3- methylglutaconic aciduria type I presented in adulthood with progressive ataxia. One patient additionally had optic atrophy, the other spasticity and dementia. Three novel mutations were found in conserved regions of the AUH gene. In both patients, MRI revealed extensive white matter disease. Follow-up MRI in a 10-year-old boy, who presented earlier with isolated febrile seizures, showed mild abnormalities in deep white matter. CONCLUSION: We define 3-methylglutaconic aciduria type I as an inborn error of metabolism with slowly progressive leukoencephalopathy clinically presenting in adulthood. In contrast to the nonspecific findings in pediatric cases, the clinical and neuroradiologic pattern in adult patients is highly characteristic. White matter abnormalities may already develop in the first decades of life. The variable features found in affected children may be coincidental. Long-term follow-up in children is essential to learn more about the natural course of this presumably slowly progressive disease. Dietary treatment with leucine restriction may be considered.

Urinary dopamine in aromatic L-amino acid decarboxylase deficiency: the unsolved paradox.

INTRODUCTION: In aromatic L-amino acid decarboxylase (AADC) deficiency, a neurotransmitter biosynthesis defect, paradoxical normal or increased levels of urinary dopamine have been reported. Genotype/phenotype correlations or alternative metabolic pathways may explain this remarkable finding, but were never studied systematically. METHODS: We studied the mutational spectrum and urinary dopamine levels in 20 patients with AADC-deficiency. Experimental procedures were designed to test for alternative metabolic pathways of dopamine production, which included alternative substrates (tyramine and 3-methoxytyrosine) and alternative enzymes (tyrosinase and CYP2D6). RESULTS/DISCUSSION: In 85% of the patients the finding of normal or increased urinary levels of dopamine was confirmed, but a relation with AADC genotype could not be identified. Renal microsomes containing CYP2D were able to convert tyramine into dopamine (3.0 nmol/min/g protein) but because of low plasma levels of tyramine this is an unlikely explanation for urinary dopamine excretion in AADC-deficiency. No evidence was found for the production of dopamine from 3-methoxytyrosine. Tyrosinase was not expressed in human kidney. CONCLUSION: Normal or increased levels of urinary dopamine are found in the majority of AADC-deficient patients. This finding can neither be explained by genotype/phenotype correlations nor by alternative metabolic pathways, although small amounts of dopamine may be formed via tyramine hydroxylation by renal CYP2D6. CYP2D6-mediated conversion of tyramine into dopamine might be an interesting target for the development of new therapeutic strategies in AADC-deficiency.

New cases of adult-onset Sandhoff disease with a cerebellar or lower motor neuron phenotype.

Sandhoff disease is a lipid-storage disorder caused by a defect in ganglioside metabolism. It is caused by a lack of functional N-acetyl-beta-d-glucosaminidase A and B due to mutations in the HEXB gene. Typical, early-onset Sandhoff disease presents before 9 months of age with progressive psychomotor retardation and early death. A late-onset form of Sandhoff disease is rare, and its symptoms are heterogeneous. As drug trials that aim to intervene in the disease mechanism are emerging, the recognition and identification of Sandhoff disease patients-particularly those with atypical phenotypes-are becoming more important. The authors describe six new late-onset Sandhoff cases demonstrating cerebellar ataxia or lower motor neuron (LMN) involvement combined with, mostly subclinical, neuropathy. Two different mutations were found: IVS 12-26 G/A and c.1514G-->A. In patients with either progressive cerebellar ataxia or LMN disease in the setting of a possibly recessive disorder, Sandhoff disease should be suspected, even when the onset age is over 45 years.