Dilemmas in genetic counseling for low-penetrance neuro-susceptibility loci detected on prenatal chromosomal microarray analysis

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Abstract

Background

Chromosomal microarray analysis is standard of care in fetuses with malformations, detecting clinically significant copy number variants in 5–7% of cases over conventional karyotyping. However, it also detects variants of uncertain significance in 1.6–4.2% of the cases, some of which are low-penetrance neuro-susceptibility loci. The interpretation of these variants in pregnancy is particularly challenging because the significance is often unclear and the clinical implications may be difficult to predict.

Objective

The purpose of this study was to describe counseling dilemmas regarding low-penetrance neuro-susceptibility loci that are detected by prenatal chromosomal microarray analysis.

Study Design

During the study period (January 2014 to December 2015), 700 prenatal chromosomal microarray analyses were performed. Cases were categorized as “indicated” (n=375) if there were abnormal sonographic findings or suggestive medical history and “patient choice” (n=325) in the presence of a structurally normal fetus with no other particular indication. The laboratory reported on copy number variants ≥400 Kb in size in loci known to be associated with genetic syndromes and ≥1 Mb in other areas of genome. Results were classified as gross aneuploidy, copy number variants, and normal. Copy number variants were categorized according to the American College of Medical Genetics standards and guidelines: pathogenic, variants of uncertain significance, or benign. Variants of uncertain significance were further subdivided into categories of likely pathogenic, variants of uncertain significance with no subclassification, and likely benign. Statistical analysis was performed with the use of Chi square test and Fisher’s exact test to compare intergroup differences in incidence of the different result categories and demographic data.

Results

Patient choice cases became more prevalent with time (35.5% in the beginning of the study, compared with 48.4% at the end of the study period). Clinically significant copy number variants were found in 14 of 375 (3.7%) of indicated cases vs only 2 of 325 (0.6%) of patient choice cases (P=.009). All “likely benign” variants consisted of low-penetrance neuro-susceptibility loci. The incidence thereof was similar between the indicated and patient choice groups (3.7% vs 3.4%; P=.85). In the indicated group, some variants of uncertain significance may have contributed to the abnormal anatomic findings. Conversely, in the patient choice group, the finding of low-penetrance neuro-susceptibility loci was often unexpected and confounding for prospective parents.

Conclusion

Prenatal chromosomal microarray analysis added clinically significant information in both groups. However, it also detected low-penetrance neuro-susceptibility loci in approximately 3.5% of the cases. This fact should be conveyed during pretest counseling to allow patients to make informed choices, particularly when chromosomal microarray is to be performed for patient choice.

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