Prenatal diagnosis of 21-hydroxylase deficiency caused by gene conversion and rearrangements: pitfalls and molecular diagnostic solutions.
OBJECTIVE
The present paper reports the prenatal diagnosis of congenital adrenal hyperplasia (CAH) in two cases of 21-hydroxylase deficiency. DNA diagnostic errors can be caused by the presence of the highly homologous 21-hydroxylase pseudogene, CYP21P, adjacent to the functional gene, CYP21. The present paper details how complex gene conversions and rearrangements between the CYP21 and CYP21P pose unique complications for prenatal diagnosis.


METHODS
Analysis of eight common mutations in the 21-hydroxylase gene as well as deletion of the entire gene is accomplished using polymerase chin reaction (PCR) followed by amplified created restriction site (ACRS) or allele-specific oligohybridization (ASO) and Southern blot followed by hybridization to a CYP21-specific probe. Linkage analysis was performed using microsatellite markers flanking the CYP21 gene.


RESULTS
The direct mutation detection assay indicated a complicated gene conversion and rearrangement in the probands of both families. Interpretation of these rearrangements made it difficult to determine whether or not the fetuses would be affected with CAH. Linkage studies revealed that each fetus had inherited both parental disease chromosomes and was therefore predicted to be affected with CAH.


CONCLUSIONS
As observed in the two reported cases, direct DNA analysis may provide limited information due to gene conversion or rearrangement between the CYP21 and CYP21P genes. These cases suggest that direct mutation detection should be supported by linkage analysis, whenever possible, to provide more comprehensive information for the family.
Mao
Rong
R
DNA Diagnostic Laboratory, University of Utah School of Medicine, Salt Lake City, UT 84108, USA. rong.mao@hsc.utah.edu
Nelson
Lesa
L
Kates
Richard
R
Miller
Christine E
CE
Donaldson
David L
DL
Tang
Wei
W
Ward
Kenneth
K
D000312:Adrenal Hyperplasia, Congenital / Q000201:enzymology* / Q000235:genetics; D002675:Child, Preschool; D002874:Chromosome Mapping; D003951:Diagnostic Errors; D005260:Female; D005785:Gene Conversion / Q000235:genetics*; D015321:Gene Rearrangement; D006801:Humans; D007223:Infant; D008297:Male; D018895:Microsatellite Repeats; D025202:Molecular Diagnostic Techniques / Q000379:methods; D015345:Oligonucleotide Probes; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D011296:Prenatal Diagnosis / Q000379:methods*; D011544:Pseudogenes; D013255:Steroid 21-Hydroxylase / Q000235:genetics*
D015345:Oligonucleotide Probes; D013255:Steroid 21-Hydroxylase