Barry Wolf

Clinical Findings in Four Children with Biotinidase Deficiency Detected through a Statewide Neonatal Screening Program

Four children with biotinidase deficiency were identified during the first year of a neonatal screening program for this disease in the Commonwealth of Virginia. Two unrelated probands were identified among the 81,243 newborn infants who were screened. In addition, two siblings of one of these infants were found to be affected. Both probands had mild neurologic symptoms at two and four months, respectively, and the two older children had more severe neurologic abnormalities, cutaneous findings, and developmental delay at two and three years of age. However, none of the affected children had acute metabolic decompensation. Previous studies have shown that the administration of biotin to affected children can be a lifesaving procedure that can reverse acute symptoms and prevent irreversible neurologic damage. Our findings demonstrate that subtle neurologic abnormalities may appear as early as at two months of age and that developmental abnormalities may occur even in the absence of episodes of overt metabolic decompensation. Since screening and treatment are both inexpensive and effective and the incidence of the disease is well within the range of that of other metabolic diseases for which screening is performed, biotinidase deficiency should be added to the group of metabolic diseases for which screening is done in the neonatal period.

Glycogen Storage Disease Type III (Glycogen Debranching Enzyme Deficiency): Correlation of Biochemical Defects with Myopathy and Cardiomyopathy

OBJECTIVEnTo determine whether a specific subtype of glycogen storage disease type III is associated with myopathy and cardiomyopathy.nnnDESIGNnCase series.nnnSETTINGnThree referral medical centers.nnnPATIENTSnAll patients with glycogen storage disease type III who were followed in 1990 and for whom both immunoblot analysis and clinical data were available.nnnMAIN OUTCOME MEASURESnEvaluation for myopathy and cardiomyopathy included determinations of serum creatine kinase activity; muscle strength testing; ischemic exercise testing; nerve conduction studies; and electromyographic, electrocardiographic, and echocardiographic studies.nnnRESULTSnThree patients with deficient debranching enzyme activity and deficient immunoreactive material in liver but normal debranching enzyme activity in muscle (glycogen storage disease IIIb) had no clinical evidence of myopathy or cardiomyopathy. Serum creatine kinase activity, muscle strength, ischemic exercise testing, electrocardiograms, and echocardiograms were normal in these patients. These studies and electromyograms were abnormal in seven patients with total debranching enzyme deficiency and an absence of immunoreactive material in both liver and muscle (glycogen storage disease IIIa) and in three patients who had debranching enzyme transferase deficiency but normal glucosidase activity in both liver and muscle (glycogen storage disease IIId). All 10 of these patients had progressive myopathy, and 6 had progressive cardiomyopathy.nnnCONCLUSIONnClinical features of glycogen storage disease type III correlate with the particular biochemical defect seen with the disorder. Assessments of debranching enzyme or debranching enzyme transferase activity in muscle can be used to predict whether patients with glycogen storage disease type III will develop myopathy and cardiomyopathy.

Neurologic symptoms of biotinidase deficiency: possible explanation

We found that the activity of biotinidase is much lower in human and rat brain or human CSF than in serum or other tissues that have biotin-dependent carboxylase activity. The brain seems to be unable to recycle biotin and depends on biotin transferred across the blood-brain barrier. The biotin-deficient state that results from an inherited lack of biotinidase results in a moderate decrease in brain pyruvate carboxylase activity. This is followed by more severe accumulation of lactate in brain than in other organs, which may explain why affected children have neurologic symptoms before many peripheral features.

Biotinidase deficiency: Accumulation of lactate in the brain and response to physiologic doses of biotin

Biotinidase deficiency is the most common cause of late onset, biotin-responsive multiple carboxylase deficiency (MCD). We studied the two oldest known boys with this disorder who had high CSF content of lactate that could have contributed to the clinical disorder. The symptoms of these patients implied that near physiologic, rather than pharmacologic, doses of biotin may be sufficient for treatment.

Nonketotic hyperglycinemia in two retarded adults A mild form of infantile nonketotic hyperglycinemia

Two mentally retarded adults with nonketotic hyperglycinemia had biochemical findings similar to those of the infantile form of the disease. Our patients differ from other adult patients and may represent the survival to adulthood of individuals with a mild form of infantile nonketotic hyperglycinemia.

Fine mapping of the human biotinidase gene and haplotype analysis of five common mutations

Biotinidase deficiency is an autosomal recessive defect in the recycling of biotin that can lead to a variety of neurologic and cutaneous symptoms. The disease can be prevented or effectively treated with exogenous biotin. The biotinidase locus (BTD) has been maped to 3p25 by in situ hybridization. The gene has been cloned, the coding region sequenced, the genomic organization determined, and a spectrum of mutations has been characterized in more than 90 individuals with profound or partial biotinidase deficiency. We have conducted haplotype analysis of 10 consanguineous and 39 nonconsanguineous probands from the United States and 8 consanguineous probands from Turkey to localize BTD with respect to polymorphic markers on 3p and to investigate the origins of five common mutations. The inbred probands were homozygous for overlapping regions of 3p ranging in size from 1.1 to 80 cM which were flanked most narrowly by D3S1259 and D3S1293. Radiation hybrids and haplotype analysis of markers within this region suggest that BTD is located within a 0.1-cM region flanked by D3S3510 and D3S1286. The radiation hybrid data suggest that the BTD gene is oriented 5′ to 3′ between the centromere and the 3p telomere. Association studies indicate that the gene is closer to a third locus D3S3613 than D3S3510, two markers which cannot be resolved by existing linkage data. The BTD locus and D3S3613 must therefore lie between D3S3510 and D3S1286. Comparison of haplotypes reveals evidence for possible founder effects for four of the five common mutations.

Fatty Acids in Biotin Deficiency

The biotin-dependent enzyme acetyl-CoA carboxylase (ACC) catalyzes the ratelimiting step in fatty acid biosynthesis. Cutaneous features similar to those in biotin deficiency are seen in essential fatty acid deficiency. In addition, since fatty acids are critical for myelination, the neurologic symptoms in biotin and biotinidase deficiency may result in part from disordered fatty acid metabolism. We have therefore compared the fatty acid composition of liver, cerebrum, and serum of biotin-deficient and control rats. Long chain fatty acid composition of total neutral lipids was measured by gas-liquid chromatography. Compared with control rats (n = 6), biotin-deficient rats (n = 6) had a marked reduction in total fatty acid content (C 14-C 27) of liver (mean control 18.5 r 3.2 pg/mg wet wt., deficient 10.8 2 1.4 kg/mg wet wt.,p < 0.001) and serum (mean control 145 * 48 mg/ml, deficient 45.5 r 17.1 mg/ml, p < 0.01). This effect was due to a relatively greater decrease in unsaturated compared with saturated fatty acids. No fatty acid abnormalities were noted in biotin-deficient rat cerebrum, consistent with a relative conservation of ACC activity in this tissue (57% of control activity) compared with that in liver (22% of control). Abnormalities in fatty acid composition in biotin deficiency may, therefore, account for some of the features of biotinidase deficiency. The absence of fatty acid abnormalities in the cerebrum may result from a longer half-life of fatty acids in the brain as compared with other tissues or from their decreased rate of synthesis a t a time when myelination is essentially complete.

763 THE CURRICULARIZATION OF McKUSICK: AN INNOVATION IN MEDICAL EDUCATION

Growing recognition of the urgent need for reform in medical education was underscored by a recent AAMC report which recommended the promotion of self education, problem solving and life long learning. We have implemented an instructional module in human genetics for first year medical students which achieved these and other desirable educational goals. During their second week in medical school each student was assigned a different entry from the 1983 edition of McKusicks Mendelian Inheritance in Man to revise and update in a semi-structured format. The resulting entries were discussed in small sections, reviewed and compiled to provide each student with a compendium of genetic disorders. Instructors found that nearly all of the important principles of Mendelian inheritance could be illustrated with the random sets of entities assigned to each discussion group. Students learned to use the library, gained an appreciation of the importance of genetic disease and were able to master clinical and experimental material with surprising ease. More than half the students spent 11-20 hours on the assignment and reviewed from 6-10 articles in detail. The caliber of the entries was significantly correlated with the time spent on the exercise, but not the number of papers reviewed, prior knowledge of the disease, the frequency with which a dictionary was used or undergraduate exposure to genetics. Student response to the exercise was favorable and raised the question of the extent to which this approach can be generalized to other disciplines.

Fatty liver and kidney syndrome in chickens as an animal model for Reye's syndrome

Fatty liver and kidney syndrome (FLKS), a naturally occurring but experimentally reproducible disease in chickens, has several clinical, pathological, and biochemical features in common with Reyes syndrome. Because of this, it has been suggested that FLKS may serve as an animal model of Reyes syndrome. We have examined, therefore, various parameters characteristic of Reyes syndrome in chickens affected with FLKS to further delineate the similarities and differences between the two disorders. Plasma glucose concentrations were significantly lower in chickens affected with FLKS which may be caused by the significantly reduced activity of pyruvate carboxylase in all FLKS-affected animals. The activity of propionyl CoA carboxylase was low in only the most severely affected chickens, and beta-methylcrotonyl CoA carboxylase showed no difference when compared with controls. This may be due to variable sensitivities of the three carboxylases to marginal biotin deficiency which occurs with FLKS. Plasma ammonia concentrations and activities of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase, however, were not elevated in the affected birds. Histological changes in the liver and kidney were noted in affected chickens, but these changes were not identical with those observed in Reyes syndrome. Although the mechanisms of nitrogen elimination in fowl differ from those in humans, failure to demonstrate hyperammonemia, elevated serum transaminase activities, or similar histological changes in tissues of affected birds indicates that FLKS is not an appropriate model for the study of Reyes syndrome.