Prenatal diagnosis of chromosomal imbalances

A multicenter study of fetal chromosomal abnormalities in Chinese women of advanced maternal age

OBJECTIVE

This study aimed to determine the rates of different fetal chromosomal abnormalities among women of advanced maternal age in China and to discuss the possible misdiagnosis risks of newer molecular techniques, for selection of appropriate prenatal screening and diagnostic technologies.

MATERIALS AND METHODS

Second trimester amniocentesis and fetal karyotype results of 46,258 women were retrospectively reviewed. All women were ≥ 35 years old with singleton pregnancies. The rates of clinically significant chromosomal abnormalities (CSCAs), incidence of chromosomal abnormalities, and correlations with age were determined.

RESULTS

From 2001 to 2010, the proportion of women of advanced maternal age undergoing prenatal diagnosis increased from 20% to 46%. The mean age was 37.4 years (range, 35-46 years). A total of 708 cases of CSCAs, with a rate of 1.53% were found. Trisomy 21 was the most common single chromosome abnormality and accounted for 55.9% of all CSCAs with an incidence of 0.86%. Trisomy 13, trisomy 18, and trisomy 21, the most common chromosome autosomal aneuploidies, accounted for 73.6% of all CSCAs, with a rate of 1.13%. As a group, the most common chromosomal aneuploidies (13/18/21/X/Y) accounted for 93.9% of all abnormalities, with a rate of 1.44%. The incidence of trisomy 21, trisomy 13/18/21 as a group, and 13/18/21/X/Y as a group was significantly greater in women aged 39 years and older (p < 0.001), but was not different between women aged 35 years, 36 years, 37 years, and 38 years.

CONCLUSION

These findings may assist in genetic counseling of advanced maternal age pregnant women, and provide a basis for the selection of prenatal screening and diagnostic technologies.

What results to disclose, when, and who decides? Healthcare professionals' views on prenatal chromosomal microarray analysis

Objectives

This study explored the views of healthcare professionals (HCPs) in the UK about what information should be disclosed, when; and whether women/parents should be given a choice as to what they wish to know.

Methods

Q‐methodology was used to assess the views of 40 HCPs (genetic HCPs, fetal medicine experts, lab‐scientists).

Results

Most participants agreed that variants of unknown clinical significance should not be disclosed. Participants were divided between those who considered variants of uncertain clinical significance helpful for parents and clinicians, and those who considered them harmful. Although recognising the potential disadvantages of disclosing risks for adult‐onset conditions, participants thought it would be difficult to withhold such information once identified. Participants largely supported some parental involvement in determining which results should be returned. Most participants believed that information obtained via CMA testing in pregnancy should either be disclosed during pregnancy, or not at all.

Conclusion

HCPs taking part in the study largely believed that variants that will inform the management of the pregnancy, or are relevant to other family members, should be reported. Recent UK guidelines, published after this research was completed, reflect these opinions. © 2016 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

What's already known about this topic?

Empirical data on healthcare professionals' (HCPs) and parents' experience with prenatal CMA are scarce.

Published data mainly focused on issues around uncertain results obtained via CMA, and on genetic health professionals.

The two main difficulties expressed by genetic counsellors associated with testing were interpreting uncertain results, and termination of pregnancies based on uncertain results

What does this study add?

It is the first study examining attitudes of a wide range of professionals involved in CMA testing: laboratory professionals, fetal medicine experts, and genetic health professionals.

We describe what types of results professionals think should or should not be disclosed and with whom they consider the onus for such decision making should lie.

These views are reflected in the recent UK guidelines about CMA testing.

Benefits and burdens of using a SNP array in pregnancies at increased risk for the common aneuploidies

We present the nature of pathogenic SNP array findings in pregnancies without ultrasound (US) abnormalities and show the additional diagnostic value of SNP array as compared with rapid aneuploidy detection and karyotyping. 1,330 prenatal samples were investigated with a 0.5-Mb SNP array after the exclusion of the most common aneuploidies. In 2.7% (36/1,330) of the cases, pathogenic chromosome aberrations were found; a microscopically detectable abnormality in 0.7% and a submicroscopic aberration in 2%. Our results show that in addition to the age- or screening-related aneuploidy risk, in pregnancies without US abnormalities, there is a risk of 1:148 (9/1,330) for a (sub)microscopic abnormality associated with an early-onset often severe disease, 1:222 (6/1,330) for a submicroscopic aberration causing an early-onset disease, 1:74 (18/1,330) for carrying a susceptibility locus for a neurodevelopmental disorder, and 1:443 (3/1,330) for a late-onset disorder (hereditary neuropathy with liability to pressure palsies in all three cases). These risk figures are important for adequate pretest counseling so that prospective parents can make informed individualized choices between targeted prenatal testing and broad testing with SNP array. Based on our results, we believe if invasive testing is performed, SNP array should be the preferred cytogenetic technique irrespective of the indication.

First fetal case of the 8q24.3 contiguous genes syndrome

Molecular cytogenetics, particularly array-CGH, opened the way to the « genotype first approach » and for the discovery of new micro rearrangement syndromes. This was the case for the 8q24.3 microdeletion syndrome. Here, we describe the phenotype of a fetus with a 8q24.3 deletion. This rare condition has to be considered as a contiguous genes syndrome because its phenotype is generated by the SCRIB and PUF60 adjacent gene endophenotypes. The fetus presented atrioventricular septal defect and hypoplastic aortic arch, facial dysmorphism, microretrognathia, dysmorphic ears, clinodactyly of the 5th digit on both hands, mild rocker bottom feet and abnormal third sacral vertebra. This fetus is the first case where the endophenotype produced by SCRIB gene is absent. This case is compared with the previous published cases.