OBJECTIVE: To investigate the clinical phenotype and genetic diagnosis process of fetuses with 21 hydroxylase deficiency (21-OHD) caused by compound heterozygous variant of the CYP21A2 gene . METHODS: A fetus who was diagnosed at Taizhou Hospital in Zhejiang Province on December 4, 2020 due to unclear characteristics of external genitalia on ultrasound was selected as the study subject. Chromosome copy number variation sequencing (CNV-seq) and whole exome sequencing (WES) were performed on amniotic fluid samples. Candidate variants were validated by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA), and short tandem repeat (STR) analysis was used to exclude maternal blood contamination. The pathogenic mechanism of the variants was further explored. The procedure followed by this study was approved by the Medical Ethics Committee of Taizhou Hospital (Ethics No.: K20201009). RESULTS: The MRI examination of the fetal external genitalia showed thickening of labia minora and enlargement of the clitoris. The CNV-seq results of the fetus showed no significant abnormality. The WES results showed that the fetus had a homozygous c.293-13C>G variant in the CYP21A2 gene (NM-000500.9). STR testing excluded maternal blood contamination. Sanger sequencing verified the presence of heterozygous c.293-13C>G variant of the CYP21A2 gene in the fetus and its mother, while its father did not detect this mutation. Further MLPA testing results showed that the fetus and its father had heterozygous deletion (I2G-C locus) mutations in exon 1~7 of the CYP21A2 gene. Based on the "Standards and Guidelines for Interpretation of Sequence Variants" jointly developed by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP), both variants of the CYP21A2 gene carried by the fetus were predicted to be pathogenic. According to the imaging and genetic testing results of the external genitalia of the fetus, the fetus was prenatally diagnosed as 21-OHD caused by the CYP21A2 gene variant. Follow-up after prenatal diagnosis showed that the couple had opted to terminate the pregnancy at a local hospital at 31⁺ weeks of gestation, and the clinical phenotype of the abortion fetus was consistent with the imaging and molecular genetic diagnosis. CONCLUSION The imaging features of this fetus are suspected to be congenital adrenal hyperplasia (CAH). Combined with WES, Sanger sequencing, and MLPA testing results, the fetus was diagnosed with 21-OHD caused by compound heterozygous variants of the CYP21A2 gene, which provided a basis for prenatal diagnosis.
Humans ; Steroid 21-Hydroxylase/genetics* ; Female ; Pregnancy ; Adrenal Hyperplasia, Congenital/diagnosis* ; Heterozygote ; Prenatal Diagnosis/methods* ; Adult ; Fetus ; DNA Copy Number Variations ; Mutation ; Genetic Testing