Prenatal diagnosis of fetal skeletal dysplasias in a tertiary Hospital in Spain

Extended genetic testing in fetuses with sonographic skeletal system abnormalities

OBJECTIVES

To analyze genetic causes of skeletal system abnormalities diagnosed by prenatal sonography and to establish a diagnostic protocol with regard to extended genetic testing in this group of patients.

METHODS

This prospective observational cohort study included all singleton pregnancies with a sonographic abnormality of the skeletal system evaluated in a single ultrasound department during a 1-year period (2019). Fetuses underwent routine genetic testing by chromosomal microarray analysis (CMA) supplemented with polyploidy testing, and those with either a normal result or an abnormal result not consistent with the observed phenotype underwent exome sequencing (ES). Interpretation of variants was discussed by a panel of specialists to identify pathogenic/likely pathogenic variants.

RESULTS

The study group comprised 55 fetuses. A chromosomal abnormality consistent with the observed phenotype was detected in 24 (43.6%) cases. After exclusions, 26 (47.3%) cases underwent further molecular testing by ES, of which 18 (69.2%) were classified as having abnormal ES results, thus increasing the diagnostic yield by a further 18 (32.7%) cases and giving an abnormal genetic test result in 42/55 (76.4%) fetuses overall. Pathogenic or likely pathogenic sequence variants in 14 different genes were detected across 18 fetuses. Seven genes are already listed in the International Skeletal Dysplasia Society Nosology and seven are not typically found to be causal for skeletal dysplasias and are not listed in the Nosology.

CONCLUSIONS

In fetuses with skeletal system anomalies, chromosomal abnormality was the most common genetic diagnosis. Exome sequencing increased the diagnostic yield over that of CMA and polyploidy testing. Fetuses with skeletal abnormalities should undergo extended genetic testing following routine testing, as many genetic anomalies responsible for skeletal defects may otherwise be missed. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Combined exome sequencing and deep phenotyping in highly selected fetuses with skeletal dysplasia during the first and second trimesters improves diagnostic yield

OBJECTIVE

To investigate the genetic etiology of skeletal dysplasia in highly selected fetuses during the first and second trimesters using deep phenotyping and exome sequencing (ES).

METHOD

Fetuses with short femurs were identified using the established prenatal diagnostic approach. A multidisciplinary team reviewed fetal phenotypic information (prenatal ultrasound findings, fetal postmortem, and radiographs) in a cohort of highly selected fetuses with skeletal dysplasia during the first and second trimesters. The affected families underwent multiplatform genetic tests.

RESULTS

Of the 27 affected fetuses, 21 (77.8%) had pathogenic or potential pathogenic variations in the following genes: COL1A1, FGFR3, COL2A1, COL1A2, FLNB, DYNC2LI1, and TRIP11. Two fetuses had compound heterozygous mutations in DYNC2LI1 and TRIP11, respectively, and the other 19 carried de novo autosomal dominant variants. Novel variants were identified in COL1A1, COL2A1, COL1A2, DYNC2LI1, and TRIP11 in 11 fetuses. We also included the first description of the phenotype of odontochondrodysplasia in a prenatal setting.

CONCLUSIONS

ES or panel sequencing offers a high diagnostic yield for fetal skeletal dysplasia during the first and second trimesters. Comprehensive and complete phenotypic information is indispensable for genetic analysis and the expansion of genotype-phenotype correlations in fetal skeletal abnormalities.