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Dihydropyrimidine dehydrogenase deficiency
Journal of the Neurological Sciences, 1987, 78:71-77
71
Elsevier JNS 2780
Dihydropyrimidine dehydrogenase deficiency Neurological aspects J.P. Braakhekke 1, W.O. Renier 1, F . J . M . Gabreals 1, R.A. De Abreu 2, J. A. J. M. Bakkeren 2 and R. C.A. Sengers 2 Institutes of 1Neurology and 2pediatrics, St. Radboud Hospital, University of Nijmegen, Nijmegen (The Netherlands) (Received 11 August, 1986) (Revised, received 12 September, 1986) (Accepted 12 September, 1986)
SUMMARY
A family with dihydropyrimidine dehydrogenase (DPD) deficiency is presented. In 3 persons a complete deficiency, and in 3 others a partial deficiency was detected in cultured fibroblasts. Two homozygote subjects and 1 heterozygote subject suffered from epileptic manifestations, in one of these homozygote subjects also microcephaly was found. DPD deficiency might be an etiological factor in the clinical picture of these patients. An autosomal recessive mode of inheritance of this deficiency was found.
Key words: Dihydropyrimidine dehydrogenase (E.C. 1.3.1.2.); Epilepsy; Inborn error of metabolism; Mental retardation; Microcephaly; Pyrimidine metabolism; Thymine; Uracil
INTRODUCTION
The first step in the catabolism of the pyrimidine bases uracil and thymine in mammalian cells is catalyzed by dihydropyrimidine dehydrogenase (DPD; E.C. 1.3.1.2). A deficiency of this enzyme causes increased levels of uracil and thymine in body fluids. Recently, we described the biochemical findings in the first patient with Correspondence address: Dr. W. O. Renier, Department of Child Neurology,Institute of Neurology, St. Radboud University Hospital, PO Box 9101, 6500 HB Nijmegen, The Netherlands. 0022-510X/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
72 D P D deficiency (Bakkeren et al. 1984). Since then 4 other patients were reported in the literature (Berger et al. 1984; Wilcken et al. 1985). Detailed clinical data of these patients were not presented, a nonspecific clinical picture of cerebral dysfunction was mentioned. Therefore, a reevaluation of the clinical data of our patient (Bakkeren et al. 1984) and her family and comparison with the other patients (Berger et al. 1984; Wilcken et al. 1985) was done in order to evaluate whether a deficiency of DPD gives rise to a specific clinical picture. CASE R E P O R T S
The pedigree of the family presented here is given in Fig. 1.
i ill
IV
2
V
v
!
Vll
Vlll
IX
MC 7
Proposit us
D ~ O Homozygotemale~ female ~r~ 9D Heterozygotemale, female Deceased E -- Epilepsy M C = M~crocephaly
Fig. 1. Pedigree of a family with dihydropyrimidine dehydrogenase deficiency.
73 Case X-2
The propositus, a 6-year-old girl, is the second child of consanguineous Dutch parents. She was born at term; height and weight were normal. Psychomotor development was unremarkable. At age 3 years, she showed ill-defined epileptic manifestations without fever. At age 4 years, an electroencephalogram (EEG) demonstrated epileptic characteristics. She was treated with phenobarbitone and ethosuximide. In 1982, she was admitted to our department for observation of her fits. She was free of medication at that time. Examination revealed a right-handed microcephalic girl (head circumference 47 cm, below 2.5 percentile), with normal height and weight. The general physical and neurological examination showed no abnormalities. Her intelligence was normal. During the clinical observation no epileptic manifestations occurred. However, an EEG, without medication, showed generalized spike-wave paroxysms on hyperventilation. Computed tomography (CT) of the brain was normal. Extensive investigations of blood, urine and ¢erebrospinal fluid (CSF) showed no abnormalities. Endocrinologic disorders and chronic infectious diseases could be ruled out. No known metabolic disorders could be detected. However, screening of urine for accumulation of organic acids revealed large amounts of uracil and thymine. Case VIII-2
The grandmother of patient X-2 is a 47-year-old woman. Her early development was unremarkable. At age 19 years she presented with generalized tonic clonic seizures. Physical and neurological examination was normal. EEG showed generalized epileptic activity on photogenic stimulation. Case IX-2
The mother of our propositus, a 28-year-old woman, is the child of a consanguineous relationship, her father is her grandfather (VII-3). She was born at term, her psychomotor development was normal. From the age of 12 years, generalized tonic clonic seizures occurred. Physical and neurological examination revealed no abnormalities. EEG showed generalized epileptic activity. CT scanning of the brain was normal. Case IX-1
The father of patient X-2 is a 38-year-old man, child of consanguineous parents. His medical history is unremarkable. Except for an essential hypertension (160/100 mm Hg), physical and neurological examination was normal. An EEG showed no abnormalities. Cases X-1 and X-3
A 10-year-old sister and a 4-year-old brother of the propositus are normal and healthy children. Their EEGs are normal. Headcircumference was normal in all subjects but one (X-2).
74 SPECIFIC INVESTIGATIONS
Methods
Uracil and thymine were detected in serum, urine and CSF with gas chromatography, combined with mass spectrometry, as described previously (Bakkeren et al. 1977; Bakkeren et al. 1984). Quantification of uracil and thymine was done with a high-performance liquid chromatograph (HPLC), equipped with a reverse phase column (De Abreu et al. 1982). DPD activity was determined in cultured fibroblasts, obtained from skin biopsy, as described previously (Bakkeren et al. 1984). In short, the supemate of lysed fibroblasts was incubated with [14C]thymine. At different times after incubation the decrease of [~4C]thymine and formation of [14C]dihydrothymine was measured by means of HPLC analysis and liquid scintillation counting of the incubation mixture. The quantity of dihydrothymine (DHT) produced was used as a measure of DPD activity. Serum was analyzed in all subjects, urine in subjects IX-I, IX-2 and X-2, CSF in patient X-2. Fibroblasts were obtained from all subjects, except from subject VIII-2. Results
High levels of uracil and thymine were present in the urine of subjects IX-2 and X-2. In subject IX-l, thymine concentration was also increased, but not as high as in the propositus, the uracil level was normal (Table 1). In serum and CSF of patient X-2 approximately the same uracil and thymine values were measured. The concentration of uracil in serum was 24 #mot/l (controls
TABLE 1 CONCENTRATIONS OF URACIL AND THYMINE IN URINE (mmol/mol creatinine), AND IN SERUM (#mol/1) Uracil
Thymine
8+ 3 594 263 6
<0.6 187 89 3
Urine
Controls (n = 36) Propositus (X-2) Mother (IX-2) Father (IX-I) Serum Controls (n = 100) Propositus (X-2) Grandmother (VIII-2) Mother (IX-2) Father (IX-l) Sister (X-l) Brother (X-3)
N D = not detectable.
0.2 + 0.2 24 5.5 15 8.2 2.6 30
ND 19 0.5 13 1.5 0.4 16
75 TABLE 2 D I H Y D R O P Y R I M I D I N E D E H Y D R O G E N A S E ACTIVITY IN C U L T U R E D F I B R O B L A S T S Activity is expressed in nmol dihydrothymine produced/rag protein, and was measured at different times after incubation. Two different batches of propositus' fibroblasts were examined. Hours atter incubation
Controls (n = 4) Propositus (X-2) Propositus (X-2) Mother (IX-2) Father (IX- 1) Sister (X-I) Brother (X-3)
0
1
2
4
6
0.03 + 0.04 0.03 0.05 0.01 0.01 0.02 0.02
0.69 + 0.13 0.01 0.01 0.01 0.35 0.28 0.03
1.25 + 0.24 0.02 0.03 0.01 0.62 0.57 0.02
2.16 + 0.45 0.02 0.03 0.01 1.07 0.91 0.02
2.50 + 0.45 0.01 0.02 -
0.2 + 0.2 #mol/1; n = 100) and in CSF 25 #mol/l (controls < 0.2 #mol/1; n = 25). The concentration of thymine in serum was 19 gmol/l (not detectable in controls; n = 100) and in CSF 15 #mol/1 (not detectable in controls; n = 25). Data concerning measurements in sera of the other members of the family are given in Table 1. The measured uracil and thymine concentrations in serum of subjects IX-2 and X-3 are comparable to those of patient X-2. Subjects VIII-2, IX-1 and X-1 had uracil and thymine concentrations between the values of controls and of the propositus. The activities of DPD are given in Table 2. In subjects IX-2, X-2 and X-3 a complete deficiency was found (no DHT production). A partial deficiency was detected in the fibroblasts of subjects IX-1 and X-I, DHT production was 0.31 and 0.28 nmol/mg protein/h, respectively (control value 0.61 + 0.10 nmol/mg protein/h, n = 4). DISCUSSION
Several factors influence urinary excretion of pyrimidines (Tuchman et al. 1985): in patients with malignancies pyrimidine excretion is increased; dietary variations influence the magnitude of uracil excretion; an increase of pyrimidine production or a decrease of the 'salvage' of pyrimidines can cause urinary excretion of excessive amounts ofpyfimidines. All these factors could be excluded in our patient and her family members. The elevated levels of uracil and thymine in CSF, urine and blood in the presented family are due to a decrease of pyrimidine degradation, caused by a deficiency of DPD. The increased levels of uracil and thymine in serum are a good reflection of the degree of enzyme deficiency. In cases IX-2, X-2 and X-3 a complete deficiency and in cases VIII-2, IX-1 and X-1 a partial deficiency of DPD is found. Analogous to other inborn errors of metabolism, a partial and a complete deficiencyof DPD are interpreted as corresponding to heterozygosity and homozygosity
76 TABLE
3
DATA ON SUBJECTS WITH A COMPLETE DEHYDROGENASE
DEFICIENCY
OF DIHYDROPYRIMIDINE
1,2,3: p a t i e n t s f r o m B e r g e r et al. (1984); 4: p a t i e n t f r o m W i l c k e n et al. 0 9 8 5 ) ; IX-2, X-2, X-3: o u r subjects.
Epilepsy Microcephaly Mental retardation
1
2
3
4
IX- 1
X-2
+ -
+ +
_ + +
a + a
+ _
+ + _
X-3
a P a t i e n t 4 d i e d at a g e 7 w e e k s . E p i l e p s y w a s n o t r e p o r t e d , m e n t a l r e t a r d a t i o n is a l m o s t n o t possible to e v a l u a t e a t this age. H o w e v e r , f r o m t h e d a t a o f the a u t h o r s it is c l e a r t h a t a p a r t f r o m a spleno- a n d h e p a t o m e g a l y a clinical e n c e p h a l o p a t h y w a s p r e s e n t .
respectively and as compatible with an autosomal recessive mode of inheritance (Berger et al. 1984). The pedigree of the presented family is in complete agreement with this mode of inheritance. A deficiency of DPD is thought to give rise to a nonspecific clinical picture of cerebral dysfunction (Berger et al. 1984). It might be that a deficiency of DPD causes functional and/or structural damage of the brain, manifestating as epilepsy, microcephaly or mental retardation. Data on subjects with a complete deficiency of DPD reported up till now are shown in Table 3. The fact that 4 of 7 subjects have epilepsy is striking. Some bias concerning the relationship between DPD deficiency and clinical picture might be present. Our data on case X-3 could suggest that a deficiency of DPD is a coincidental finding in these subjects. On the other hand, it is possible that in this boy the first symptoms eventually will appear in the future, as was the case in subjects VIII-2 and IX-2. The pathophysiological mechanisms involved in the occurrence of neurological signs and symptoms in patients with a deficiency of DPD are unclear. Pyfimidine nucleotides enter into nucleic acid synthesis. Already in 1959 it was suggested that seizure etiology might be found at the nucleic acid level (Morell 1959). The pyrimidine nueleoside uridine has anticonvulsant effects in animals with experimental seizure phenomena, indicating that uridine and its related compounds play a role of vital importance in regulating nervous system activity (Roberts 1973). Pyrimidine nucleosides are involved in cerebral carbohydrate metabolism, in cerebral phospholipid metabolism, and are able to modify some mitochondrial enzymatic activities (Dagani et al. 1984). Disturbances of pyrimidine metabolism by anti-metabolites in cancer treatment are thought to be responsible for neurotoxicity presenting as seizures (Wiley et al. 1982). So, there are arguments that inborn errors of pyrimidine metabolism might cause a neurological picture, especially epilepsy. Whatsoever, up till now it can only be suggested that DPD deficiency is an etiological factor in some patients with neurological signs and symptoms. The prognosis of the clinical picture, associated with DPD dofieiency is variable. In Berget's patient 1
77 (Berger et al. 1984) and in our patient X-2, the clinical condition became unremarkable after a period during which epileptic manifestations occurred. Epilepsy in our subjects VIII-2 and IX-2 is under control with anti-epileptic drugs. In patients 2 and 3 of Berger et al. (1984) mental retardation remained unchanged. The patient of Wilcken et al. (1985) with clinical signs of an encephalopathy died because of tracheal aspiration. Up till now there are no indications that DPD deficiency gives rise to progressive, deteriorating neurological pictures. In conclusion, it seems justified to promote the analysis of pyrimidine catabolism in patients with epilepsy, mental retardation or microcephaly and in their family members in order to further analyse the role of DPD deficiency as an etiological factor in these clinical pictures. ACKNOWLEDGEMENT
We thank the Studygroup on Genetic Counseling, St. Radboud University Hospital, for support in unraveling the pedigree of the family. REFERENCES Bakkeren, J.A.J.M., R.C.A. Sengers, J.M.F. Trijbels and P.H.A.T. Engels (1977) Organic aciduria in hypoxic premature newborns simulating an inborn error of metabolism, Europ..L Pediat., 127: 41-47. B akkeren, J. A. J. M., R. A. De Abreu, R. C. A. Sengers, F. J. M. Gabre~ls, J. M. Maas and W. O. Renier (1984) Elevated urine, blood and cerebrospinal fluid levels of uracil and thymine in a child with dihydrothymine dehydrogenase deficiency, Clin. Chim. Acta, 140: 247-256. Berger, R., S.A. Stoker-De Vries, S.K. Wadman, M. Duran, F.A. Beemer, P.K. De Bree, J.J. Weits-Binnerts, T.J. Penders and J.K. Van der Woude (1984) Dihydropyrimidine dehydrogenase deficiency leading to thymine-uraciluria. An inborn error of pyrimidine metabolism, Clin. Chim. Acta, 141: 227-234. Dagani, F., F. Marzatico, D. Curti, M. Taglietti, F. Zanada and G. Benzi (1984) Influence of intermittent hypoxia and pyrimidinic nucleosides on cerebral enzymatic activities related to energy transduction, Neurochem. Res., 9: 1085-1099. De Abreu, R. A., J. M. Van Baal, C. H. M. M. De Bruyn, J. A. J. M. B akkeren and E. D. A. M. Schretlen (1982) High-performance liquid chromatographic determination of purine and pyrimidine bases, ribonucleosides, deoxyribonucleosides and cyclic ribonucleotides in biological fluids, J. Chromatogr., 229: 67-75. Morrell, F. (1959) Experimental focal epilepsy in animals, Arch. Neurol. (Chic.), 1: 140-147. Roberts, C.A. (1973) Anticonvulsant effects of uridine: comparative analysis of metrazol and penicillin induced foci, Brain Res., 55: 291-308. Tuchman, M., J. S. Stoeckeler, D.T. Kiang, R. F. O'Dea, M. L. Ramnaralne and B. L. Mirkin (1985) Familial pyrimidinemia and pyrimidinuria associated with severe fluorouracil toxicity, N. Engl. J. Med., 313: 245-249. Wilcken, B., J. Hammond, R. Berger, G. Wise and C. James (1985) Dihydropyrimidine dehydrogenase deficiency - - A further case, J. Inher. Metab. D/s., 8 (Suppl. 2): 115-116. Wiley, R.G., R.J. Gralla, E.S. Casper and N. Kemeny (1982) Neurotoxicity of the pyrimidine synthesis inhibitor N-phosphonoacetyl-t-aspartate, Ann. Neurol., 12: 175-183.
71
Elsevier JNS 2780
Dihydropyrimidine dehydrogenase deficiency Neurological aspects J.P. Braakhekke 1, W.O. Renier 1, F . J . M . Gabreals 1, R.A. De Abreu 2, J. A. J. M. Bakkeren 2 and R. C.A. Sengers 2 Institutes of 1Neurology and 2pediatrics, St. Radboud Hospital, University of Nijmegen, Nijmegen (The Netherlands) (Received 11 August, 1986) (Revised, received 12 September, 1986) (Accepted 12 September, 1986)
SUMMARY
A family with dihydropyrimidine dehydrogenase (DPD) deficiency is presented. In 3 persons a complete deficiency, and in 3 others a partial deficiency was detected in cultured fibroblasts. Two homozygote subjects and 1 heterozygote subject suffered from epileptic manifestations, in one of these homozygote subjects also microcephaly was found. DPD deficiency might be an etiological factor in the clinical picture of these patients. An autosomal recessive mode of inheritance of this deficiency was found.
Key words: Dihydropyrimidine dehydrogenase (E.C. 1.3.1.2.); Epilepsy; Inborn error of metabolism; Mental retardation; Microcephaly; Pyrimidine metabolism; Thymine; Uracil
INTRODUCTION
The first step in the catabolism of the pyrimidine bases uracil and thymine in mammalian cells is catalyzed by dihydropyrimidine dehydrogenase (DPD; E.C. 1.3.1.2). A deficiency of this enzyme causes increased levels of uracil and thymine in body fluids. Recently, we described the biochemical findings in the first patient with Correspondence address: Dr. W. O. Renier, Department of Child Neurology,Institute of Neurology, St. Radboud University Hospital, PO Box 9101, 6500 HB Nijmegen, The Netherlands. 0022-510X/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
72 D P D deficiency (Bakkeren et al. 1984). Since then 4 other patients were reported in the literature (Berger et al. 1984; Wilcken et al. 1985). Detailed clinical data of these patients were not presented, a nonspecific clinical picture of cerebral dysfunction was mentioned. Therefore, a reevaluation of the clinical data of our patient (Bakkeren et al. 1984) and her family and comparison with the other patients (Berger et al. 1984; Wilcken et al. 1985) was done in order to evaluate whether a deficiency of DPD gives rise to a specific clinical picture. CASE R E P O R T S
The pedigree of the family presented here is given in Fig. 1.
i ill
IV
2
V
v
!
Vll
Vlll
IX
MC 7
Proposit us
D ~ O Homozygotemale~ female ~r~ 9D Heterozygotemale, female Deceased E -- Epilepsy M C = M~crocephaly
Fig. 1. Pedigree of a family with dihydropyrimidine dehydrogenase deficiency.
73 Case X-2
The propositus, a 6-year-old girl, is the second child of consanguineous Dutch parents. She was born at term; height and weight were normal. Psychomotor development was unremarkable. At age 3 years, she showed ill-defined epileptic manifestations without fever. At age 4 years, an electroencephalogram (EEG) demonstrated epileptic characteristics. She was treated with phenobarbitone and ethosuximide. In 1982, she was admitted to our department for observation of her fits. She was free of medication at that time. Examination revealed a right-handed microcephalic girl (head circumference 47 cm, below 2.5 percentile), with normal height and weight. The general physical and neurological examination showed no abnormalities. Her intelligence was normal. During the clinical observation no epileptic manifestations occurred. However, an EEG, without medication, showed generalized spike-wave paroxysms on hyperventilation. Computed tomography (CT) of the brain was normal. Extensive investigations of blood, urine and ¢erebrospinal fluid (CSF) showed no abnormalities. Endocrinologic disorders and chronic infectious diseases could be ruled out. No known metabolic disorders could be detected. However, screening of urine for accumulation of organic acids revealed large amounts of uracil and thymine. Case VIII-2
The grandmother of patient X-2 is a 47-year-old woman. Her early development was unremarkable. At age 19 years she presented with generalized tonic clonic seizures. Physical and neurological examination was normal. EEG showed generalized epileptic activity on photogenic stimulation. Case IX-2
The mother of our propositus, a 28-year-old woman, is the child of a consanguineous relationship, her father is her grandfather (VII-3). She was born at term, her psychomotor development was normal. From the age of 12 years, generalized tonic clonic seizures occurred. Physical and neurological examination revealed no abnormalities. EEG showed generalized epileptic activity. CT scanning of the brain was normal. Case IX-1
The father of patient X-2 is a 38-year-old man, child of consanguineous parents. His medical history is unremarkable. Except for an essential hypertension (160/100 mm Hg), physical and neurological examination was normal. An EEG showed no abnormalities. Cases X-1 and X-3
A 10-year-old sister and a 4-year-old brother of the propositus are normal and healthy children. Their EEGs are normal. Headcircumference was normal in all subjects but one (X-2).
74 SPECIFIC INVESTIGATIONS
Methods
Uracil and thymine were detected in serum, urine and CSF with gas chromatography, combined with mass spectrometry, as described previously (Bakkeren et al. 1977; Bakkeren et al. 1984). Quantification of uracil and thymine was done with a high-performance liquid chromatograph (HPLC), equipped with a reverse phase column (De Abreu et al. 1982). DPD activity was determined in cultured fibroblasts, obtained from skin biopsy, as described previously (Bakkeren et al. 1984). In short, the supemate of lysed fibroblasts was incubated with [14C]thymine. At different times after incubation the decrease of [~4C]thymine and formation of [14C]dihydrothymine was measured by means of HPLC analysis and liquid scintillation counting of the incubation mixture. The quantity of dihydrothymine (DHT) produced was used as a measure of DPD activity. Serum was analyzed in all subjects, urine in subjects IX-I, IX-2 and X-2, CSF in patient X-2. Fibroblasts were obtained from all subjects, except from subject VIII-2. Results
High levels of uracil and thymine were present in the urine of subjects IX-2 and X-2. In subject IX-l, thymine concentration was also increased, but not as high as in the propositus, the uracil level was normal (Table 1). In serum and CSF of patient X-2 approximately the same uracil and thymine values were measured. The concentration of uracil in serum was 24 #mot/l (controls
TABLE 1 CONCENTRATIONS OF URACIL AND THYMINE IN URINE (mmol/mol creatinine), AND IN SERUM (#mol/1) Uracil
Thymine
8+ 3 594 263 6
<0.6 187 89 3
Urine
Controls (n = 36) Propositus (X-2) Mother (IX-2) Father (IX-I) Serum Controls (n = 100) Propositus (X-2) Grandmother (VIII-2) Mother (IX-2) Father (IX-l) Sister (X-l) Brother (X-3)
N D = not detectable.
0.2 + 0.2 24 5.5 15 8.2 2.6 30
ND 19 0.5 13 1.5 0.4 16
75 TABLE 2 D I H Y D R O P Y R I M I D I N E D E H Y D R O G E N A S E ACTIVITY IN C U L T U R E D F I B R O B L A S T S Activity is expressed in nmol dihydrothymine produced/rag protein, and was measured at different times after incubation. Two different batches of propositus' fibroblasts were examined. Hours atter incubation
Controls (n = 4) Propositus (X-2) Propositus (X-2) Mother (IX-2) Father (IX- 1) Sister (X-I) Brother (X-3)
0
1
2
4
6
0.03 + 0.04 0.03 0.05 0.01 0.01 0.02 0.02
0.69 + 0.13 0.01 0.01 0.01 0.35 0.28 0.03
1.25 + 0.24 0.02 0.03 0.01 0.62 0.57 0.02
2.16 + 0.45 0.02 0.03 0.01 1.07 0.91 0.02
2.50 + 0.45 0.01 0.02 -
0.2 + 0.2 #mol/1; n = 100) and in CSF 25 #mol/l (controls < 0.2 #mol/1; n = 25). The concentration of thymine in serum was 19 gmol/l (not detectable in controls; n = 100) and in CSF 15 #mol/1 (not detectable in controls; n = 25). Data concerning measurements in sera of the other members of the family are given in Table 1. The measured uracil and thymine concentrations in serum of subjects IX-2 and X-3 are comparable to those of patient X-2. Subjects VIII-2, IX-1 and X-1 had uracil and thymine concentrations between the values of controls and of the propositus. The activities of DPD are given in Table 2. In subjects IX-2, X-2 and X-3 a complete deficiency was found (no DHT production). A partial deficiency was detected in the fibroblasts of subjects IX-1 and X-I, DHT production was 0.31 and 0.28 nmol/mg protein/h, respectively (control value 0.61 + 0.10 nmol/mg protein/h, n = 4). DISCUSSION
Several factors influence urinary excretion of pyrimidines (Tuchman et al. 1985): in patients with malignancies pyrimidine excretion is increased; dietary variations influence the magnitude of uracil excretion; an increase of pyrimidine production or a decrease of the 'salvage' of pyrimidines can cause urinary excretion of excessive amounts ofpyfimidines. All these factors could be excluded in our patient and her family members. The elevated levels of uracil and thymine in CSF, urine and blood in the presented family are due to a decrease of pyrimidine degradation, caused by a deficiency of DPD. The increased levels of uracil and thymine in serum are a good reflection of the degree of enzyme deficiency. In cases IX-2, X-2 and X-3 a complete deficiency and in cases VIII-2, IX-1 and X-1 a partial deficiency of DPD is found. Analogous to other inborn errors of metabolism, a partial and a complete deficiencyof DPD are interpreted as corresponding to heterozygosity and homozygosity
76 TABLE
3
DATA ON SUBJECTS WITH A COMPLETE DEHYDROGENASE
DEFICIENCY
OF DIHYDROPYRIMIDINE
1,2,3: p a t i e n t s f r o m B e r g e r et al. (1984); 4: p a t i e n t f r o m W i l c k e n et al. 0 9 8 5 ) ; IX-2, X-2, X-3: o u r subjects.
Epilepsy Microcephaly Mental retardation
1
2
3
4
IX- 1
X-2
+ -
+ +
_ + +
a + a
+ _
+ + _
X-3
a P a t i e n t 4 d i e d at a g e 7 w e e k s . E p i l e p s y w a s n o t r e p o r t e d , m e n t a l r e t a r d a t i o n is a l m o s t n o t possible to e v a l u a t e a t this age. H o w e v e r , f r o m t h e d a t a o f the a u t h o r s it is c l e a r t h a t a p a r t f r o m a spleno- a n d h e p a t o m e g a l y a clinical e n c e p h a l o p a t h y w a s p r e s e n t .
respectively and as compatible with an autosomal recessive mode of inheritance (Berger et al. 1984). The pedigree of the presented family is in complete agreement with this mode of inheritance. A deficiency of DPD is thought to give rise to a nonspecific clinical picture of cerebral dysfunction (Berger et al. 1984). It might be that a deficiency of DPD causes functional and/or structural damage of the brain, manifestating as epilepsy, microcephaly or mental retardation. Data on subjects with a complete deficiency of DPD reported up till now are shown in Table 3. The fact that 4 of 7 subjects have epilepsy is striking. Some bias concerning the relationship between DPD deficiency and clinical picture might be present. Our data on case X-3 could suggest that a deficiency of DPD is a coincidental finding in these subjects. On the other hand, it is possible that in this boy the first symptoms eventually will appear in the future, as was the case in subjects VIII-2 and IX-2. The pathophysiological mechanisms involved in the occurrence of neurological signs and symptoms in patients with a deficiency of DPD are unclear. Pyfimidine nucleotides enter into nucleic acid synthesis. Already in 1959 it was suggested that seizure etiology might be found at the nucleic acid level (Morell 1959). The pyrimidine nueleoside uridine has anticonvulsant effects in animals with experimental seizure phenomena, indicating that uridine and its related compounds play a role of vital importance in regulating nervous system activity (Roberts 1973). Pyrimidine nucleosides are involved in cerebral carbohydrate metabolism, in cerebral phospholipid metabolism, and are able to modify some mitochondrial enzymatic activities (Dagani et al. 1984). Disturbances of pyrimidine metabolism by anti-metabolites in cancer treatment are thought to be responsible for neurotoxicity presenting as seizures (Wiley et al. 1982). So, there are arguments that inborn errors of pyrimidine metabolism might cause a neurological picture, especially epilepsy. Whatsoever, up till now it can only be suggested that DPD deficiency is an etiological factor in some patients with neurological signs and symptoms. The prognosis of the clinical picture, associated with DPD dofieiency is variable. In Berget's patient 1
77 (Berger et al. 1984) and in our patient X-2, the clinical condition became unremarkable after a period during which epileptic manifestations occurred. Epilepsy in our subjects VIII-2 and IX-2 is under control with anti-epileptic drugs. In patients 2 and 3 of Berger et al. (1984) mental retardation remained unchanged. The patient of Wilcken et al. (1985) with clinical signs of an encephalopathy died because of tracheal aspiration. Up till now there are no indications that DPD deficiency gives rise to progressive, deteriorating neurological pictures. In conclusion, it seems justified to promote the analysis of pyrimidine catabolism in patients with epilepsy, mental retardation or microcephaly and in their family members in order to further analyse the role of DPD deficiency as an etiological factor in these clinical pictures. ACKNOWLEDGEMENT
We thank the Studygroup on Genetic Counseling, St. Radboud University Hospital, for support in unraveling the pedigree of the family. REFERENCES Bakkeren, J.A.J.M., R.C.A. Sengers, J.M.F. Trijbels and P.H.A.T. Engels (1977) Organic aciduria in hypoxic premature newborns simulating an inborn error of metabolism, Europ..L Pediat., 127: 41-47. B akkeren, J. A. J. M., R. A. De Abreu, R. C. A. Sengers, F. J. M. Gabre~ls, J. M. Maas and W. O. Renier (1984) Elevated urine, blood and cerebrospinal fluid levels of uracil and thymine in a child with dihydrothymine dehydrogenase deficiency, Clin. Chim. Acta, 140: 247-256. Berger, R., S.A. Stoker-De Vries, S.K. Wadman, M. Duran, F.A. Beemer, P.K. De Bree, J.J. Weits-Binnerts, T.J. Penders and J.K. Van der Woude (1984) Dihydropyrimidine dehydrogenase deficiency leading to thymine-uraciluria. An inborn error of pyrimidine metabolism, Clin. Chim. Acta, 141: 227-234. Dagani, F., F. Marzatico, D. Curti, M. Taglietti, F. Zanada and G. Benzi (1984) Influence of intermittent hypoxia and pyrimidinic nucleosides on cerebral enzymatic activities related to energy transduction, Neurochem. Res., 9: 1085-1099. De Abreu, R. A., J. M. Van Baal, C. H. M. M. De Bruyn, J. A. J. M. B akkeren and E. D. A. M. Schretlen (1982) High-performance liquid chromatographic determination of purine and pyrimidine bases, ribonucleosides, deoxyribonucleosides and cyclic ribonucleotides in biological fluids, J. Chromatogr., 229: 67-75. Morrell, F. (1959) Experimental focal epilepsy in animals, Arch. Neurol. (Chic.), 1: 140-147. Roberts, C.A. (1973) Anticonvulsant effects of uridine: comparative analysis of metrazol and penicillin induced foci, Brain Res., 55: 291-308. Tuchman, M., J. S. Stoeckeler, D.T. Kiang, R. F. O'Dea, M. L. Ramnaralne and B. L. Mirkin (1985) Familial pyrimidinemia and pyrimidinuria associated with severe fluorouracil toxicity, N. Engl. J. Med., 313: 245-249. Wilcken, B., J. Hammond, R. Berger, G. Wise and C. James (1985) Dihydropyrimidine dehydrogenase deficiency - - A further case, J. Inher. Metab. D/s., 8 (Suppl. 2): 115-116. Wiley, R.G., R.J. Gralla, E.S. Casper and N. Kemeny (1982) Neurotoxicity of the pyrimidine synthesis inhibitor N-phosphonoacetyl-t-aspartate, Ann. Neurol., 12: 175-183.