Can biochemical analysis be performed on a Chorionic Villus Sampling (CVS) sample?

Biochemical Analysis on Chorionic Villus Sampling (CVS) Samples

Yes, biochemical analysis can be performed on chorionic villus sampling (CVS) samples, particularly for the diagnosis of certain genetic disorders including collagen disorders and single-gene conditions. 1

Types of Biochemical Analyses Possible with CVS

• Biochemical analysis of type I collagen synthesized by cultured chorionic villi cells can be offered for conditions like osteogenesis imperfecta (OI) when collagen screening studies have been completed on an affected parent or previous affected infant and shown to be abnormal 1
• DNA-based diagnoses of mendelian (single-gene) conditions, such as cystic fibrosis, hemophilia, muscular dystrophy, and hemoglobinopathies, can be made by direct analysis of uncultured chorionic villus cells 1
• Direct analysis of uncultured chorionic villus cells is a more efficient method than culturing amniocytes for certain genetic analyses 1

Timing and Process

• CVS is typically performed between 10-12 weeks gestation, providing earlier results than amniocentesis (which is usually performed at 15-18 weeks) 1
• The time from CVS biopsy to final diagnosis for biochemical analysis is approximately 3-4 weeks 1
• CVS can be performed either transabdominally or transvaginally 2

Special Considerations for CVS Samples

• Methylation analysis in CVS samples has unique properties that must be considered when performing certain genetic tests 1
• The FMR1 region (relevant for Fragile X testing) usually does not have methylation associated with X-inactivation in chorionic villi, and may or may not have hypermethylation associated with full mutations if the CVS procedure was performed before 12.5 weeks gestation 1
• When testing DNA extracted from chorionic villi for conditions like Fragile X syndrome, methylation analysis is optional 1

Limitations and Potential Issues

• CVS has a higher rate of sampling and technical failures compared to amniocentesis 2
• Maternal cell contamination can occur in approximately 1.8% of cases for the culture method 3
• In some cases (approximately 5.7% in one study), patients may require a subsequent amniocentesis in the same pregnancy due to issues such as absent or insufficient villi (3.3%), culture failure (0.23%), or specimen contamination (0.15%) 4
• Unlike amniocentesis, CVS cannot be used for alphafetoprotein (AFP) testing, which is useful for neural tube defect screening 1

Advantages of CVS for Biochemical Analysis

• Earlier diagnosis allows for earlier decision-making regarding pregnancy management 1
• When combined with techniques like FISH (fluorescence in situ hybridization), results can be obtained within 24 hours for certain analyses 5
• The earlier timing of CVS is associated with lower maternal morbidity and mortality if pregnancy termination is chosen based on results 1

For genetic disorders like osteogenesis imperfecta, biochemical analysis of CVS samples provides a valuable first-trimester diagnostic option when a family history of the condition exists 1.