The Zellweger syndrome: Book review and bibliography. The cerebro-hepato-renal syndrome of Zellweger. L.C.P. Govaerts. Nijmegen: Stichting Studentenpers, 1984, 195 pp

Paul Dyken Lecture of the Southern Pediatric Neurology Society. Inherited neurodegenerative disease: the evolution of our thinking

The past 3 decades have witnessed impressive progress in our understanding of inherited neurometabolic diseases, promoted by the rapid development and application of molecular genetic strategies. Such progress has required the juxtaposition of clinical evaluations and basic science techniques. The central role of careful and complete assessment of affected children cannot be overemphasized and in no way has been diminished by technologic advances. Indeed, enhanced clinical and laboratory evaluations have led to important conceptual advances. Molecular genetics has elucidated those disorders with known metabolic defects through functional cloning and explained the variability of disease expression based on specific mutational events. Alternatively, positional cloning has identified molecular defects for those disorders with clear phenotypic patterns, but lacking a defined metabolic abnormality. Regarding heterogeneous expression, disorders with clearly different phenotypes can arise from different mutations within the same gene. The multiple variants of beta-hexosaminidase deficiency (Tay-Sachs disease) are, arguably, the best examples. Conversely, disorders with similar phenotypes are explainable by quite different mutational events. In addition, the identification of specific diseases exhibiting both biochemical abnormalities and disturbed organogenesis has blurred conventional dogma regarding separation of genetic disorders into strict metabolic and structural categories. Disorders of peroxisomal function and the neuronal ceroid lipofuscinoses are prototypes for the points noted above and raise important issues regarding our approaches to children with these disorders. These issues include a high index of suspicion for an inherited neurometabolic disease and an open mind to possible interrelations with other known and seemingly dissimilar conditions.

Peroxisomal disorders in neurology

Although peroxisomes were initially believed to play only a minor role in mammalian metabolism, it is now clear that they catalyse essential reactions in a number of different metabolic pathways and thus play an indispensable role in intermediary metabolism. The metabolic pathways in which peroxisomes are involved include the biosynthesis of ether phospholipids and bile acids, the oxidation of very long chain fatty acids, prostaglandins and unsaturated long chain fatty acids and the catabolism of phytanate and (in man) pipecolate and glyoxylate. The importance of peroxisomes in cellular metabolism is stressed by the existence of a group of inherited diseases, the peroxisomal disorders, caused by an impairment in one or more peroxisomal functions. In the last decade our knowledge about peroxisomes and peroxisomal disorders has progressed enormously and has been the subject of several reviews. New developments include the identification of several additional peroxisomal disorders, the discovery of the primary defect in several of these peroxisomal disorders, the recognition of novel peroxisomal functions and the application of complementation analysis to obtain information on the genetic relationship between the different peroxisomal disorders. The peroxisomal disorders recognized at present comprise 12 different diseases, with neurological involvement in 10 of them. These diseases include: (1) those in which peroxisomes are virtually absent leading to a generalized impairment of peroxisomal functions (the cerebro-hepato-renal syndrome of Zellweger, neonatal adrenoleukodystrophy, infantile Refsum disease and hyperpipecolic acidaemia); (2) those in which peroxisomes are present and several peroxisomal functions are impaired (the rhizomelic form of chondrodysplasia punctata, combined peroxisomal beta-oxidation enzyme protein deficiency); and (3) those in which peroxisomes are present and only a single peroxisomal function is impaired (X-linked adrenoleukodystrophy, peroxisomal thiolase deficiency (pseudo-Zellweger syndrome), acyl-CoA oxidase deficiency (pseudo-neonatal adrenoleukodystrophy) and probably, the classic form of Refsum disease.

Peroxisomal disorders: clinical commentary and future prospects

Recent progress in the classification, biochemistry, and molecular biology of peroxisomal disorders is reviewed from a clinical perspective. Diseases such as Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, hyperpipecolic acidemia, chondrodysplasia punctata, and Leber amaurosis share a common phenotype and involve deficiency of multiple peroxisomal enzymes. These disorders are associated with diverse metabolic abnormalities which are useful in pre- or postnatal diagnosis and distinguish these disorders from others such as X-linked adrenoleukodystrophy, adult Refsum disease, hyperoxaluria type I, and acatalasemia. Peroxisome structure is difficult to quantify histologically, since recent studies emphasize its developmental variability and tissue heterogeneity. The ability to manipulate this structure by dietary or pharmaceutical means provides a novel approach to therapy. At the molecular level, deficiency of peroxisomal enzymes responsible for fatty acid beta-oxidation or ether lipid synthesis reflects enhanced protein degradation due to abnormal peroxisomes; messenger RNA for the beta-oxidation enzymes is transcribed normally in peroxisomal disorders and can be increased by peroxisome proliferators. At least one integral structural protein of the peroxisome is synthesized normally in Zellweger syndrome. Hypotheses for the basic defect include defective regulation, uptake, or coenzyme stimulation of imported proteins, as well as defective biosynthesis. One clue to this defect may be a similar evolutionary history of peroxisomes and mitochondria which would explain their common alteration in Zellweger syndrome.

The Neu-Laxova syndrome in female sibs: clinical and pathological features with prenatal diagnosis in the second sib

We report on affected sisters with the Neu-Laxova syndrome. Prenatal diagnosis of the condition was achieved by serial ultrasound examinations which demonstrated abnormal fetal growth in the second affected fetus before 24 weeks gestation.