defective coupling of to adenylyl cyclase. This 
diminution of bioactivity was not associated with 
reduced immunologic levels of aG^ to adenylyl cy- 
clase. The defect in G^ bioactivity was limited to car- 
diac and skeletal muscle, occurred only in animals 
homozygous for the dystrophic trait, and was de- 
monstrable before any cardiac abnormalities were 
evident on light microscopic examination of the 
hearts. The molecular basis for this functional alter- 
ation of G^ remains under investigation. 
Finally, acute ethanol ingestion diminishes car- 
diac contractility; therefore Dr. Van Dop and his 
colleagues investigated the direct effects of ethanol 
on adenylyl cyclase activation in isolated cardiac 
membranes from normal hearts. Ethanol had no ef- 
fects on basal activity or on manganous ion-medi- 
ated activation of adenylyl cyclase. However, activa- 
tion of adenylyl cyclase by the nonhydrolyzable 
guanine nucleotide analogue guanylyl imidodi- 
phosphate and by fluoride ion was enhanced by 
ethanol. Similarly, ethanol also increased activity 
of adenylyl cyclase in membranes that had been 
pretreated with isoproterenol and guanylyl im- 
idodiphosphate. Ethanol thus appears to enhance 
acutely the coupling between activated G^ and the 
catalytic subunit of adenylyl cyclase. Further investi- 
gations of the mechanisms by which ethanol dimin- 
ishes excitation-contraction coupling in the heart 
continue. 
II. Molecular Lesions of Steroid 21 -Hydroxylase in 
Salt-losing Congenital Adrenal Hyperplasia. 
Genetic deficiency of the enzyme 21 -hydroxylase 
is the most frequent cause of salt-losing congenital 
adrenal hyperplasia (CAH), an autosomal recessive 
disorder of adrenal steroidogenesis. The CAH lo- 
cus, located within the major histocompatibility 
complex between HIA-B and HLA-D on chromo- 
some 6p, consists of a tandem duplicated pair of 
genes encoding steroid 21 -hydroxylase (CYP21) 
and the two fourth components of complement 
(C4A and C4B). One 21 -hydroxylase gene {CYP21B) 
PUBLICATIONS 
is expressed while the second gene (CYP21A) is a 
highly homologous pseudogene containing several 
deleterious mutations that prevent expression of 
active enzyme. Salt-losing CAH, the most severe 
form of CAH, frequently occurs with deletion of the 
CYP21B gene, which apparently results following 
unequal crossing over between the active gene and 
the pseudogene. In collaboration with Drs. Claude 
Migeon and Patricia Donohoue (The Johns Hopkins 
University), Dr. Van Dop has mapped the crossover 
sites in chimeric, recombinant CYP21 genes from 
six patients with salt-losing CAH. Nucleotide se- 
quences unique to the CYP21A pseudogene or to 
the active CYP21B gene were mapped, using gene- 
specific restriction sites and oligonucleotide hybrid- 
izations. Each chimeric CYP21 gene in the CYP21- 
deletion-linked haplotypes contained sequences 
near the 5 ' end that were characteristic of CYP21A 
and only a single transition of sequences of CYP21A 
to sequences of CYP21B to the 3' end. These nucle- 
otide sequence transitions all occurred within one 
of two discrete regions. All eight chimeric CYP21 
genes coupled with HLA-Bw47 in five unrelated pa- 
tients had the CYP21A-CYP21B sequence transition 
within the same gene region (+1,375 to +1,993). 
One of the three other CPP2i5-deletion haplotypes 
had a sequence transition within this same region, 
while in two other haplotypes the transition oc- 
curred between base pairs +470 and +999. Similar 
analysis of a haplotype with a gene conversion of 
the CYP21B gene to CyP21A suggests that sequen- 
tial, multiple crossings over or a single gene conver- 
sion affecting a long segment of the CYP21B gene 
produces the gene conversion genotypes that also 
occur in patients with salt-losing CAH. 
Dr. Van Dop was Assistant Professor of Pediatrics 
at Harvard Medical School and Director of the En- 
docrinology and Clinical Research Center Core Lab- 
oratories at Children's Hospital in Boston when 
these studies were conducted. He is now Associate 
Professor of Pediatrics at the University of California 
School of Medicine at Los Angeles. 
Articles 
Donohoue, PA., Jospe, N., Migeon, C.J., and Van Dop, C. 1989. Two distinct areas of unequal crossingover 
within the steroid 21 -hydroxylase genes produce absence of CYP21B. Genomics 5:397-406. 
Feldman, A.M., Gates, A.E., Bristow, M.R., and Van Dop, C. 1989. Altered expression of the a-subunits of 
G proteins in failing human hearts. J Mol Cell Cardiol 21:359-365. 
Continued 
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