Tyrosine hydroxylase deficiency is an autosomal recessive disorder resulting from cerebral catecholamine deficiency. Tyrosine hydroxylase deficiency has been reported in fewer than 40 patients worldwide. To recapitulate all available evidence on clinical phenotypes and rational diagnostic and therapeutic approaches for this devastating, but treatable, neurometabolic disorder, we studied 36 patients with tyrosine hydroxylase deficiency and reviewed the literature. Based on the presenting neurological features, tyrosine hydroxylase deficiency can be divided in two phenotypes: an infantile onset, progressive, hypokinetic-rigid syndrome with dystonia (type A), and a complex encephalopathy with neonatal onset (type B). Decreased cerebrospinal fluid concentrations of homovanillic acid and 3-methoxy-4-hydroxyphenylethylene glycol, with normal 5-hydroxyindoleacetic acid cerebrospinal fluid concentrations, are the biochemical hallmark of tyrosine hydroxylase deficiency. The homovanillic acid concentrations and homovanillic acid/5-hydroxyindoleacetic acid ratio in cerebrospinal fluid correlate with the severity of the phenotype. Tyrosine hydroxylase deficiency is almost exclusively caused by missense mutations in the TH gene and its promoter region, suggesting that mutations with more deleterious effects on the protein are incompatible with life. Genotype-phenotype correlations do not exist for the common c.698G>A and c.707T>C mutations. Carriership of at least one promotor mutation, however, apparently predicts type A tyrosine hydroxylase deficiency. Most patients with tyrosine hydroxylase deficiency can be successfully treated with l-dopa.

Summary:Purpose: When monothempy with antiepileptic drugs (AEDs) fails, combination therapy is tried in an attempt to improve effectiveness by improving efficacy, tolerability, or both. We reviewed the available studies (both animal and human) on AED polytherapy to determine whether AEDs can be selected for combination therapy based on their mechanisms of action, and if so, which cornbinations are associated with increased effectiveness. Because various designs and methods of analysis were used in these studies, it was also necessary to evaluate the appropriateness of these approaches.Methods: Published papers reporting on AED polytherapy in animals or humans were identified by Medline search and by checking references cited in these papers.Results: Thirty-nine papers were identified reporting on twodrug AED combinations. Several combinations were reported to offer improved effectiveness, but no uniform approach was used in either animal or human studies for the evaluation of pharmacodynamic drug interactions; efficacy was often the only end point. Conclusions:There is evidence that AED polytherapy based on mechanisms of action may enhance effectiveness. In particular, combining a sodium channel blocker with a drug enhancing GABAergic inhibition appears to be advantageous. Combining two GABA mimetic drugs or combining an AMPA antagonist with an NMDA antagonist may enhance efficacy, but tolerability is sometimes reduced. Combining two sodium channel blockers seeins less promising. However, given the incomplete knowledge of the pathophysiology of seizures and indeed of the exact mechanisms of action of AEDs, an empirical but rational approach for evaluating AED combinations is of fundamental importance. This would involve appropriate testing of all possible combinations in animal models and subsequent evaluation of advantageous combinations in clinical trials. Testing procedures in animals should include the isobologram method, and the concept of drug load should be the basis of studies in patients with epilepsy.

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Summary: Purpose:We reviewed the literature to determine whether an analysis of published data could clarify the relationship between antiepileptic drug (AED) polytherapy and adverse affects (AE). We highlight the problems encountered.Methods: We made a Medline-search for articles published between 1974 and 1994 reporting the number of AE and doses or serum levels of every AED, per patient or treatment group, and used the PDD/DDD ratio to calculate AED load per patient from doses or the OSL/AToxL ratio to do so from serum levels of individual drugs. The PDD/ DDD is the sum of ratios of the actual prescribed daily doses divided by the published average therapeutic dose of each drug. The OSL/AToxL is the sum of each observed serum level divided by its average toxic level.Results: We retrieved 118 trial reports. Most had to be excluded because of incomplete reporting of concomitant medication or AE. The data of the 15 articles selected for further analysis indicate a relationship between drug load and number of AE. We noted no relationship between the number of AEDs administered and AE. In add-on studies, the difference in neurotoxicity between the active and placebo arm may be obscured if the relative increase in drug load is small, as exemplified by the study of McGuire et al. (35).Conclusions: Articles reporting add-on trials of new AEDs generally do not provide detailed information about the basic medication to which the new AED is added, which makes calculation of total drug load impossible. Furthermore, often only frequency of A E is reported, not severity or development of tolerance, making it difficult to judge the impact of AE. However, despite the paucity of available information, we present some evidence that toxicity in AED polytherapy may be related to total drug load, rather than to the number of drugs administered. Therefore, the present trend to reject polytherapy for fear of increased toxicity is not warranted, which removes one of the objections to initiating specific research to prove or disprove the value of AED combinations as long as the drug load is appropriate. Key Words: PolytherapyAntiepileptic drugs-Adverse effects-Drug loadEpilepsy.Antiepileptic drug (AED) pharmacotherapy is aimed at reducing seizure frequency and severity without producing adverse effects (AE). However, the reporting of AE in clinical trials lacks quantitative data because AE are often described in terms of frequency and rarely in terms of severity (1). Although the incidence of AE is important, the degree to which they occur also determines the acceptability of individual AEDs. When quantitative data are presented, a comparison is complicated because of the different rating scales used (2,3).The risk of development of chronic toxicity has been one of the arguments against use of polypharmacy in epilepsy (4). Much of this toxicity is believed Accepted January 13, 1997. Address correspondence and reprint requests to Dr. H. Meinardi, c/o P.O. Box 21,2100 AA Heemstede, The Netherlands.to be directly related to the number ...