Dopaminergic modulation of the reward system in schizophrenia: a placebo-controlled dopamine depletion fMRI study

BACKGROUND

The brain reward circuitry innervated by dopamine is critically disturbed in schizophrenia. This study aims to investigate the role of dopamine-related brain activity during prediction of monetary reward and loss in first episode schizophrenia patients.

METHODS

We measured blood-oxygen-level dependent (BOLD) activity in 10 patients with schizophrenia (SCH) and 12 healthy controls during dopamine depletion with α-methylparatyrosine (AMPT) and during a placebo condition (PLA).

RESULTS

AMPT reduced the activation of striatal and cortical brain regions in SCH. In SCH vs. controls reduced activation was found in the AMPT condition in several regions during anticipation of reward and loss, including areas of the striatum and frontal cortex. In SCH vs. controls reduced activation of the superior temporal gyrus and posterior cingulate was observed in PLA during anticipation of rewarding stimuli. PLA patients had reduced activation in the ventral striatum, frontal and cingulate cortex in anticipation of loss. The findings of reduced dopamine-related brain activity during AMPT were verified by reduced levels of dopamine in urine, homovanillic-acid in plasma and increased prolactin levels.

CONCLUSIONS

Our results indicate that dopamine depletion affects functioning of the cortico-striatal reward circuitry in SCH. The findings also suggest that neuronal functions associated with dopamine neurotransmission and attribution of salience to reward predicting stimuli are altered in schizophrenia.

Dopamine metabolism in adults with 22q11 deletion syndrome, with and without schizophrenia--relationship with COMT Val¹⁰⁸/¹⁵⁸Met polymorphism, gender and symptomatology

22q11 Deletion syndrome (22q11DS) is a major risk factor for schizophrenia. In addition, both conditions are associated with alterations of the dopaminergic system. The catechol-O-methyltransferase (COMT) gene, located within the deleted region, encodes for the enzyme COMT that is important for degradation of catecholamines, including dopamine (DA). COMT activity is sexually dimorphic and its gene contains a functional polymorphism, Val¹⁰⁸/¹⁵⁸ Met; the Met allele is associated with lower enzyme activity. We report the first controlled catecholamine study in 22q11DS-related schizophrenia. Twelve adults with 22q11DS with schizophrenia (SCZ+) and 22 adults with 22q11DS without schizophrenia (SCZ-) were genotyped for the COMT Val¹⁰⁸/¹⁵⁸ Met genotype. We assessed dopaminergic markers in urine and plasma. We also correlated these markers with scores on the Positive and Negative Symptom Scale (PANSS). Contrary to our expectations, we found SCZ+ subjects to be more often Val hemizygous and SCZ- subjects more often Met hemizygous. Significant COMT cross gender interactions were found on dopaminergic markers. In SCZ+ subjects there was a negative correlation between prolactin levels and scores on the general psychopathology subscale of the PANSS scores. These findings suggest intriguing, but complex, interactions of the COMT Val¹⁰⁸/¹⁵⁸ Met polymorphism, gender and additional factors on DA metabolism, and its relationship with schizophrenia.

Dopaminergic modulation of the human reward system: a placebo-controlled dopamine depletion fMRI study

Reward related behaviour is linked to dopaminergic neurotransmission. Our aim was to gain insight into dopaminergic involvement in the human reward system. Combining functional magnetic resonance imaging with dopaminergic depletion by α-methylparatyrosine we measured dopamine-related brain activity in 10 healthy volunteers. In addition to blood-oxygen-level-dependent (BOLD) contrast we assessed the effect of dopaminergic depletion on prolactin response, peripheral markers for dopamine and norepinephrine. In the placebo condition we found increased activation in the left caudate and left cingulate gyrus during anticipation of reward. In the α-methylparatyrosine condition there was no significant brain activation during anticipation of reward or loss. In α-methylparatyrosine, anticipation of reward vs. loss increased activation in the right insula, left frontal, right parietal cortices and right cingulate gyrus. Comparing placebo versus α-methylparatyrosine showed increased activation in the left cingulate gyrus during anticipation of reward and the left medial frontal gyrus during anticipation of loss. α-methylparatyrosine reduced levels of dopamine in urine and homovanillic acid in plasma and increased prolactin. No significant effect of α-methylparatyrosine was found on norepinephrine markers. Our findings implicate distinct patterns of BOLD underlying reward processing following dopamine depletion, suggesting a role of dopaminergic neurotransmission for anticipation of monetary reward.

Disrupted dopaminergic neurotransmission in 22q11 deletion syndrome

22q11 Deletion syndrome (22q11DS) is associated with chromosome 22q11 microdeletions and high rates of psychiatric disorders. Susceptibility for these disorders could be explained by haploinsufficiency of the catechol-O-methyltransferase gene, which encodes an enzyme involved in dopamine (DA) breakdown. It is unknown how dopaminergic neurotransmission is affected in people with 22q11DS. To date, there have been no controlled studies investigating dopaminergic neurotransmission in people with 22q11DS. We report the results of a challenge study in high-functioning adults with 22q11DS and age- and gender-matched controls using neuro-endocrine and peripheral dopaminergic markers. At baseline, 22q11DS subjects compared to controls had higher urine DA levels and lower plasma levels of the predominant DA metabolite homovanillic acid (HVA). Following DA depletion, 22q11DS subjects showed lower urine and plasma HVA levels and a lower prolactin response than controls. The ratio of DA/HVA, a rough index of DA turnover, was significantly higher in the 22q11DS subjects at baseline and after DA depletion. Our results suggest that adults with 22q11DS have disrupted dopaminergic neurotransmission, which might explain their susceptibility for psychiatric disorders.

Aromatic l-aminoacid decarboxylase deficiency: unusual neonatal presentation and additional findings in organic acid analysis

Aromatic l-aminoacid decarboxylase (AADC) deficiency is a neurotransmitter defect leading to a combined deficiency of catecholamines and serotonin. Patients are usually detected in infancy due to developmental delay, hypotonia, and extrapyramidal movements. Diagnosis is based on an abnormal neurotransmitter metabolite profile in CSF and reduced AADC activity in plasma. An elevation of vanillactic acid (VLA) has been described as the only abnormality detected in organic acid analysis (OA) of urine. We report a patient who presented in the neonatal period with lethargy, hypotonia, metabolic acidosis, and hypoglycemia. Blood ammonia, lactic acid, and acylcarnitines were normal, but OA of a urine sample showed a small increase of VLA, raising the suspicion of AADC deficiency. The patient was lost to follow-up until the age of 8 months, when he presented with dystonia, abnormal movements, oculogyric crises, and hypothermia. Repeat OA showed not only increased levels of VLA, but also increased vanilpyruvic acid (VPA), N-acetyl-vanilalanine (AVA) and N-acetyl-tyrosine (NAT). Neurotransmitter analysis in CSF showed increased vanilalanine (1200 nmol/L, ref<100) with decreased levels of 5-hydroxy-indoleacetic acid (5-HIAA, < 5 nmol/L; ref 152-462), homovanillic acid (HVA, 83 nmol/L; ref 302-845), and methoxy-hydroxy-phenyl-glycol (<5 nmol/L; ref 51-112). AADC activity in plasma was nearly undetectable. In the urine, low excretion of vanilmandelic acid (<0.3 micromol/mmol creat; ref 0.3-20) and 5-HIAA (0.9 micromol/mmol creat; ref 4-18), was found, but HVA was normal and dopamine even elevated. This contradictory phenomenon of hyperdopaminuria has been described earlier in AADC deficient patients. We postulate that VPA and AVA could originate from vanilalanine (through a transaminase and an acetylase respectively), while NAT could originate from tyrosine through an AA acetylase. This report expands the clinical presentation of AADC deficiency and adds new markers of the disease for OA analysis, improving detection of AADC deficient patients in general metabolic screening procedures.

A novel neurodevelopmental syndrome responsive to 5-hydroxytryptophan and carbidopa

Tryptophan hydroxylase (TPH; EC 1.14.16.4) catalyzes the first rate-limiting step of serotonin biosynthesis by converting l-tryptophan to 5-hydroxytryptophan. Serotonin controls multiple vegetative functions and modulates sensory and alpha-motor neurons at the spinal level. We report on five boys with floppiness in infancy followed by motor delay, development of a hypotonic-ataxic syndrome, learning disability, and short attention span. Cerebrospinal fluid (CSF) analysis showed a 51 to 65% reduction of the serotonin end-metabolite 5-hydroxyindoleacetic acid (5HIAA) compared to age-matched median values. In one out of five patients a low CSF 5-methyltetrahydrofolate (MTHF) was present probably due to the common C677T heterozygous mutation of the methylenetetrahydrofolate reductase (MTHFR) gene. Baseline 24-h urinary excretion showed diminished 5HIAA values, not changing after a single oral load with l-tryptophan (50-70 mg/kg), but normalizing after 5-hydroxytryptophan administration (1 mg/kg). Treatment with 5-hydroxytryptophan (4-6 mg/kg) and carbidopa (0.5-1.0 mg/kg) resulted in clinical amelioration and normalization of 5HIAA levels in CSF and urine. In the patient with additional MTHFR heterozygosity, a heterozygous missense mutation within exon 6 (G529A) of the TPH gene caused an exchange of valine by isoleucine at codon 177 (V177I). This has been interpreted as a rare DNA variant because the pedigree analysis did not provide any genotype-phenotype correlation. In the other four patients the TPH gene analysis was normal. In conclusion, this new neurodevelopmental syndrome responsive to treatment with 5-hydroxytryptophan and carbidopa might result from an overall reduced capacity of serotonin production due to a TPH gene regulatory defect, unknown factors inactivating the TPH enzyme, or selective loss of serotonergic neurons.

Prolidase deficiency among an Israeli population: prenatal diagnosis in a genetic disorder with uncertain prognosis

Prolidase deficiency is an autosomal recessive disorder that is characterized by considerable inter- and intrafamilial variability in its clinical presentation, ranging from asymptomatic to severe and fatal illness. We report here, for the first time, prenatal diagnosis of prolidase deficiency in a family whose first child was severely affected since birth and died at an early age. However, unexpectedly, the parents decided to continue the second pregnancy, which produced a full-term, healthy-appearing baby. The diagnosis of severe prolidase deficiency was confirmed in the baby's leukocytes. At age 4 months the baby is asymptomatic. Since the clinical severity of the disorder cannot be predicted, genetic counselling remains problematic despite the feasibility of prenatal diagnosis.

Localization of a gene for molybdenum cofactor deficiency, on the short arm of chromosome 6, by homozygosity mapping

Molybdenum cofactor deficiency (MoCoD) is a fatal disorder manifesting, shortly after birth, with profound neurological abnormalities, mental retardation, and severe seizures unresponsive to any therapy. The disease is a monogenic, autosomal recessive disorder, and the existence of at least two complementation groups suggests genetic heterogeneity. In humans, MoCoD leads to the combined deficient activities of sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. By using homozygosity mapping and two consanguineous affected kindreds of Israeli-Arab origin, including five patients, we demonstrated linkage of a MoCoD gene to an 8-cM region on chromosome 6p21.3, between markers D6S1641 and D6S1672. Linkage analysis generated the highest combined LOD-score value, 3.6, at a recombination fraction of 0, with marker D6S1575. These results now can be used to perform prenatal diagnosis with microsatellite markers. They also provide the only tool for carrier detection of this fatal disorder.

Hyperaminoaciduria identifies patients at risk of developing renal tubular toxicity associated with ifosfamide and platinate containing regimens

We monitored renal tubular function in 18 neuroblastoma patients treated with chemotherapeutic regimens containing Ifosfamide and platinates. The total IFO dose ranged from 30 to 48 g/m2. After each IFO course and at regular intervals during follow-up 24 hour urinary exception of aminoacids, qualitative excretion of protein and glucose, tubular reabsorption of phosphate, serum pH, and liver enzyme (SGOT and SGPT) were measured. The ratio of alpha-amino-Nitrogen/total-Nitrogen (normal less than 2.5%) and the urinary excretion pattern were used to quantify the aminoaciduria in 12 out of 15 evaluable patients some degree of tubular toxicity occurred during treatment, slowly progressing to a Debré-de Toni-Fanconi syndrome (DTFS) in 7 patients. The DTFS was fully developed in most cases 3-9 months after the end of treatment and was reversible in 3 cases. Hyperaminoaciduria (HAA) occurred in all patients during treatment, preceding other signs of tubular toxicity. The maximum ratio measured before development of a DTFS was significantly higher in the patients with severe toxicity (P less than .01). HAA characterized by a ratio greater than 10% predicts the development of a DTFS with a sensitivity of 71.4% and a specificity of 87.4%.