Nico G. G. M. Abeling

Genotype and phenotype in patients with dihydropyrimidine dehydrogenase deficiency

Abstract Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disease characterised by thymine-uraciluria in homozygous deficient patients and has been associated with a variable clinical phenotype. In order to understand the genetic and phenotypic basis for DPD deficiency, we have reviewed 17 families presenting 22 patients with complete deficiency of DPD. In this group of patients, 7 different mutations have been identified, including 2 deletions [295–298delTCAT, 1897delC], 1 splice-site mutation [IVS14+1G>A)] and 4 missense mutations (85T>C, 703C>T, 2658G>A, 2983G>T). Analysis of the prevalence of the various mutations among DPD patients has shown that the G→A point mutation in the invariant splice donor site is by far the most common (52%), whereas the other six mutations are less frequently observed. A large phenotypic variability has been observed, with convulsive disorders, motor retardation and mental retardation being the most abundant manifestations. A clear correlation between the genotype and phenotype has not been established. An altered β-alanine, uracil and thymine homeostasis might underlie the various clinical abnormalities encountered in patients with DPD deficiency.

Brown-Vialetto-Van Laere and Fazio Londe syndrome is associated with a riboflavin transporter defect mimicking mild MADD: a new inborn error of metabolism with potential treatment

We report on three patients (two siblings and one unrelated) presenting in infancy with progressive muscle weakness and paralysis of the diaphragm. Metabolic studies revealed a profile of plasma acylcarnitines and urine organic acids suggestive of a mild form of the multiple acyl-CoA dehydrogenation defect (MADD, ethylmalonic/adipic acid syndrome). Subsequently, a profound flavin deficiency in spite of a normal dietary riboflavin intake was established in the plasma of all three children, suggesting a riboflavin transporter defect. Genetic analysis of these patients demonstrated mutations in the C20orf54 gene which encodes the human homolog of a rat riboflavin transporter. This gene was recently implicated in the Brown-Vialetto-Van Laere syndrome, a rare neurological disorder which may either present in infancy with neurological deterioration with hypotonia, respiratory insufficiency and early death, or later in life with deafness and progressive ponto-bulbar palsy. Supplementation of riboflavin rapidly improved the clinical symptoms as well as the biochemical abnormalities in our patients, demonstrating that high dose riboflavin is a potential treatment for the Brown-Vialetto-Van Laere syndrome as well as for the Fazio Londe syndrome which is considered to be the same disease entity without the deafness.

Inborn errors of pyrimidine degradation: clinical, biochemical and molecular aspects

The pyrimidines, uracil and thymine, are degraded in four steps. The first three steps of pyrimidine catabolism, controlled by enzymes shared by both pathways, result in the production of the neurotransmitter amino acid β-alanine from uracil and the nonfunctional (R)-(-)-β-aminoisobutyrate from thymine. The fourth step is controlled by several aminotransferases, which have different affinities for β-alanine, β-aminoisobutyrate and GABA. Defects concerning the first three steps all lead to a reduced production of β-alanine; defects of the transaminases involving the metabolism of β-alanine and GABA lead to accumulation of these neurotransmitter substances. In addition, other metabolites will accumulate or be reduced depending on the specific enzyme defect. Analysis of the abnormal concentrations of these metabolites in the body fluids is essential for the detection of patients with pyrimidine degradation defects. Clinically these disorders are often overlooked because symptomatology is highly aspecific. The growth in our knowledge concerning inborn errors of pyrimidine degradation has emphasized the importance of the clinical awareness of these defects as a possible cause of neurological disease and a contraindication for treatment of cancer patients with certain pyrimidine analogues. The various defects are discussed and attention is paid to clinical, genetic and diagnostic aspects.

Etiology of mental retardation in children referred to a tertiary care center: a prospective study.

A prospective assessment following a step-wise protocol in 281 patients with unexplained cognitive delay was used to assess diagnostic possibilities. Diagnostic procedures were complex and required a multidisciplinary approach. One third of diagnoses was established based on clinical history and physical exam only; for another third, clinical history and physical exam provided essential clues for additional investigations; and a third were established by additional investigations only. The likelihood to reach a diagnosis did not depend on the severity of mental retardation. We found that in a tertiary care center, a diagnosis can be established in 1 out of every 2 patients. Clinical history and physical examination are the most important instruments to reach a diagnosis.

Plasma and erythrocyte fatty acid patterns in patients with recurrent depression: a matched case-control study.

Background The polyunsaturated fatty acid (PUFA) composition of (nerve) cell membranes may be involved in the pathophysiology of depression. Studies so far, focussed mainly on omega-3 and omega-6 PUFAs. In the present study, saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and PUFAs of the omega-3, -6 and -9 series in plasma and erythrocytes of patients with recurrent major depressive disorder (MDD-R) were compared with controls. Methodology and Principal Findings We carried out a case-control study. The sample consisted of 137 patients with MDD-R and 65 matched non-depressed controls. In plasma and erythrocytes of patients with MDD-R the concentrations of most of the SFAs and MUFAs, and additionally erythrocyte PUFAs, all with a chain length >20 carbon (C) atoms, were significantly lower than in the controls. In contrast, the concentrations of most of the shorter chain members (≤18C) of the SFAs and MUFAs were significantly higher in the patients. Estimated activities of several elongases in plasma of patients were significantly altered, whereas delta-9 desaturase activity for C14∶0 and C18∶0 was significantly higher. Conclusions/Significance The fatty acid status of patients with MDD-R not only differs with regard to omega-3 and omega-6 PUFAs, but also concerns other fatty acids. These alterations may be due to: differences in diet, changes in synthesizing enzyme activities, higher levels of chronic (oxidative) stress but may also result from adaptive strategies by providing protection against enhanced oxidative stress and production of free radicals.

The Brown-Vialetto-Van Laere and Fazio Londe syndrome revisited: natural history, genetics, treatment and future perspectives

The Brown-Vialetto-Van Laere syndrome is a rare neurological disorder which may present at all ages with sensorineural deafness, bulbar palsy and respiratory compromise. Fazio-Londe syndrome is considered to be the same disease entity. Recently it was demonstrated that in some patients the disease is caused by mutations in the SLC52A3 gene which encodes the intestinal (hRFT2) riboflavin transporter. In these patients riboflavin deficiency is the cause of the BVVL/FL syndrome and supplementation of riboflavin proved a life saving treatment. Mutations in the SLC52A2 gene and the SLC52A1 (GPR172B) gene, coding for human riboflavin transporters hRFT3 and hRFT1 have been associated with the BVVL syndrome as well. We performed a review of the literature, with emphasis on the natural history and the effects of treatment in these patients. A total of 35 publications were traced reporting on the clinical presentation of 74 patients who presented before age 18. The most prevalent symptoms were bulbar palsy, hearing loss, facial weakness and respiratory compromise. Death was reported in 28 of the 61 untreated patients, with a very low survival in patients presenting before age 4. All 13 patients who were treated with riboflavin survived, with a strong clinical improvement after days to months of treatment in eight patients. Three patients demonstrated a stable clinical course and treatment was stopped early in two patients. Abnormalities in plasma flavin levels and/or plasma acylcarnitine profiles were observed in some but not in all patients, and also patients with normal plasma flavin levels and acylcarnitine profiles demonstrated a striking clinical improvement on riboflavin supplementation. It is now clear that proper diagnosis requires mutation analysis of all three transporter genes and treatment should be started immediately without first awaiting results of molecular analysis. Clinical improvement may be rapid or gradual over a period of more than 12 months.

Eniluracil Treatment Completely Inactivates Dihydropyrimidine Dehydrogenase in Colorectal Tumors

PURPOSE To determine the effect of eniluracil on colorectal tumor dihydropyrimidine dehydrogenase (DPD) activity. PATIENTS AND METHODS Patients who were to undergo primary colorectal tumor resection received oral eniluracil 10 mg/m(2) twice daily for 3 days before surgery. Mononuclear cells were obtained before the start of eniluracil and on the morning of surgery, to measure DPD activity, protein, and mRNA. Plasma uracil was also measured at these two time points to assess the effect of eniluracil on pyrimidine accumulation. DPD activity, protein, and mRNA were also assessed in colorectal tumors and adjacent normal mucosa of patients who received eniluracil and untreated control patients. RESULTS DPD activity in tumors from 10 untreated patients ranged from 30 to 92 pmol/min/mg of protein. In contrast, there was no detectable tumor DPD activity in 10 patients who received eniluracil. A similar pattern was observed in mononuclear cells, where median pretherapy activity was 366.5 pmol/min/mg of protein (range, 265 to 494 pmol/min/mg of protein) and was undetectable immediately before surgery. Plasma uracil changed from a median less than 0.2 micromol/L before therapy to 27.76 micromol/L before surgery. No difference in DPD protein or mRNA was observed between pretherapy and presurgery mononuclear cell samples or between treated and untreated tumor samples. CONCLUSION This study provides definitive evidence that eniluracil completely inactivates DPD activity in human solid tumors. The increased plasma uracil and decreased DPD activity are consistent with systemic inactivation of the enzyme. The mechanism of inactivation is at the catalytic level, because no changes in DPD protein or mRNA were observed. Treatment with eniluracil will eliminate DPD activity as a source of pharmacokinetic fluorouracil variability or resistance in human colorectal cancer.

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.

Tyrosine hydroxylase deficiency unresponsive to L-dopa treatment with unusual clinical and biochemical presentation

Tyrosine hydroxylase (TH) deficiency is generally considered as a cause of the autosomal recessive form of dopa-responsive dystonia, also known as Segawa disease. Clinical hallmarks comprise parkinsonian and other extrapyramidal symptoms. Biochemically the defect leads to the defective synthesis of catecholamines, in particular dopamine. The diagnosis relies on a characteristic pattern of biogenic amine metabolites exclusively in the CSF and can be confirmed by establishing a mutation in the TH gene. Here we present a patient meeting all diagnostic criteria, including a new homozygous mutation (926T>C) with confirmed parental heterozygosity, extrapyramidal symptoms, but atypical other symptoms with periodic neurological episodes observed every 4 days and unresponsive to dopa treatment. The CSF biochemical abnormalities were severe. Uncharacteristically, a strongly abnormal urinary catecholamine metabolite pattern was also consistently observed. The atypical presentation of this patient shows that the clinical and metabolic phenotype of TH deficiency is more variable than formerly thought, and that the condition should no longer be considered as a treatable disorder per se.

An aetiological study of 25 mentally retarded adults with autism

Autism is a chronic and severe neuropsychiatric disorder with an early onset, characterised by qualitative impairments of social interaction, deviant development of language and other communicative skills, delayed cognitive development, and restricted repetitive and stereotyped interests and behaviours.1,2 The prevalence in the general population was estimated at 5.5/10 000 but more recent investigations report higher rates.3 Males are affected more often than females, with a predominance of 3 to 1.4 Mental retardation is present in about 75 to 85% of patients with autism,1,5,6 and almost half of all autistic patients are functionally mute.5 The causes and mechanisms underlying autism are heterogeneous, varying from genetic causes, that is, chromosome abnormalities and conditions with Mendelian inheritance such as metabolic disturbances, to infectious causes and teratogenic influences.7–9 The prevailing view is that autism is caused by a pathophysiological process arising from the interaction of an early environmental insult and a genetic predisposition.10 However, the aetiology often remains obscure and earlier studies reported that causal medical conditions were detectable in a relatively small percentage of autistic patients.11,12 There is increasing evidence that genetic factors may well play a major role in the remaining idiopathic cases.13 In support of this hypothesis is the recent identification of deletions in the short arm of the X chromosome,14 duplications of the Prader-Willi/Angelman critical region on chromosome 15q,15,16 linkage to 7q31 and 2q,17,18 as well as the high monozygotic twin concordance rates,19,20 and high recurrence risk among sibs of patients with idiopathic autism.21 Autism poses an extremely heavy burden for affected subjects, their families, and society. Research focusing on biological causes and on guidelines for these studies in each specific person is important, both in diagnostics, management, …