Jia-Huan Ding

Medium-Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency: The Prevalent Mutation G985 (K304E) Is Subject to a Strong Founder Effect from Northwestern Europe

Medium-chain acyl CoA dehydrogenase (MCAD) deficiency is a potentially fatal inherited defect of fatty acid beta-oxidation. Approximately 90% of the disease-causing alleles in diagnosed patients are due to a single base mutation, an A (adenine) to G (guanine) transition at position 985 of MCAD cDNA (G985). In a limited number of cases it was found that this mutation was always associated with a particular haplotype, defined by three intragenic restriction fragment length polymorphisms, indicating a founder effect [Kølvraa et al.; Hum Genet 1991; 87: 425-429]. In addition, recent studies of American patients and their ancestors suggested the existence of a founder from northern Europe [Yokota et al.; Am J Hum Genet 1991; 49: 1280-1291]. In the present study we document (1) that the G985 heterozygous frequency in the Caucasian population of North Carolina in the USA is 1/84, which is 5- to 10-fold higher than in non-Caucasian Americans; (2) that there exists a 100% association of the G985 mutation in 17 families with MCAD-deficient patients to a certain haplotype, defined by the restriction endonucleases BanII, PstI and TaqI; (3) that MCAD deficiency due to the G985 mutation is more frequent in the Netherlands, Ireland, England, Belgium and Denmark than in other western European countries, and (4) that the frequency distribution of G985 mutation carriers is 1/68-1/101 in newborns in the United Kingdom and Denmark, and 1/333 in Italy. These results support the notion of a founder effect in northwestern Europe.

Mild cystic fibrosis linked to chromosome 7q22 markers with an uncommon haplotype

Cystic fibrosis is the commonest autosomal recessive genetic disorder among northern Europeans and their descendants. Recently, investigators have mapped the gene for cystic fibrosis to chromosome 7. We report the results of DNA linkage analysis in a consanguineous family with mild cystic fibrosis. The probes used in this study were pmet D. pmet H, XV-2c, KM.19, and pJ3.11. Linkage to the identified cystic fibrosis locus of 7q22 was established with a peak logarithm of the odds (lod) score of 3.00 at a recombination fraction theta =0.00 using the tightly linked marker KM.19. In addition, we found the D haplotype, which is not commonly associated with cystic fibrosis, to be segregating in this family. The D haplotype is composed of the 1.4-kb allele detectable by XV-2c and the 6.6-kb allele detectable by KM.19. The three patients with cystic fibrosis who had consanguineous parents were homozygous DD, were among the least severely affected, and had no pancreatic insufficiency. The five patients with unrelated parents were heterozygous for the D haplotype and the commoner B haplotype, except one patient who was homozygous DD. All affected persons with pancreatic insufficiency had the DB genotype. These DNA linkage studies provide additional evidence for the existence of a cystic fibrosis allele that is associated with mild disease.

Vitamins E and K induce aryl hydrocarbon hydroxylase activity in human cell cultures

Two fat soluble vitamins, Vitamins E and K, when added into culture medium, were found to increase aryl hydrocarbon hydroxylase activity in human cultured cells. The extent of induction in a hepatoma-derived cell line (Hep G2) by these vitamins is of similar magnitude to those cells receiving benz[a]anthracene; whereas in a mammary tumor-derived cell line (MCF-7), benz[a]anthracene is the best inducer for the hydroxylase activity. The increase of the hydroxylase activity is associated with increased levels of a specific mRNA coding for polynuclear aromatic hydrocarbons-induced form of cytochrome P-450 with Vitamins E and K treatment. The size of the induced mRNA is 3.3 kilobase which is the same as that of benz[a]anthracene treatment.

Type III glycogen storage disease: An adult case with mild disease but complete absence of debrancher protein☆

A 54-yr-old woman who presented with chest pain and elevated serum creatine kinase levels was found to have type III glycogen storage disease. Except for a history of hepatomegaly in childhood, she was healthy and lived a normal life. There was no hypoglycemia, seizure disorder or growth retardation. Muscle weakness was not apparent until the sixth decade. Despite the mild clinical course, debranching enzyme activity was not detectable by biochemical assay, and immunoblot analysis using a polyclonal antibody showed a complete absence of debrancher protein. Thus, mild clinical manifestations in this patient could not be explained by the residual debrancher enzyme and/or activity.

LONG-CHAIN 3-HYDROXYACYL-COA DEHYDROGENASE DEFICIENCY: THE MAJOR DISEASE-CAUSING MUTATION AND DIAGNOSIS. 851

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, an autosomal recessive disorder of fatty acid oxidation, is clinically characterized by skeletal myopathy, Reye-like syndrome or sudden unexplained infant death. A common mutation G1528C has recently been reported (Ij1st, L. 1994). To screen a large number of patients, we have developed a double PCR/Pst I digestion method. Here, we report mutation studies in eleven additional unrelated patients with LCHAD deficiency. Genomic DNA fragments (117 bp) were amplified by double PCR, digested with Pst I and subjected to electrophoresis on 12% polyacrylamide gel. The G1528C mutation in four patients were found to be homozygous; seven patients were compound heterozygous, indicating significant genetic heterogeneity. Furthermore, this DNA test combined with tandem mass spectrometric in vitro probe analysis could easily recognize the affected individuals and the mutation carrier in the family with compound heterozygous for G1528C. “Supported by the Courtwright-Summers Research Fund.”