Fetal phenotypes of Mendelian disorders: A descriptive study from India

Exome sequencing (ES)-based diagnosis of Mendelian diseases in the fetus is limited by paucity of phenotypic information. This study reports the comprehensive phenotypes of some fetuses with Mendelian disorders.

Next generation technology-based sequencing of all coding regions of the genome (Exome sequencing) or targeted gene sequencing using Sanger or next generation platforms was performed in a cohort of deeply phenotyped, cytogenetically normal fetuses with morphological defects. Prenatal ultrasonographic phenotypes and postmortem details including dysmorphology, histopathology, and radiography were ascertained. Novel candidate genes, novel/unusual findings, and unusual genotypes in cases with confirmed Mendelian disorders are described.

Of the 102 fetuses sequenced, 45 (44%) achieved definitive diagnosis of a Mendelian disorder with 50 pathogenic/likely pathogenic variants. The majority (87%) were autosomal recessive, 69% families were consanguineous, and 54% variants were novel. Dysmorphic syndromes, skeletal dysplasias, and metabolic disorders were the commonest disease categories, ciliopathies and dystroglycanopathies, commonest molecular categories. We describe the first fetal description of six monogenic diseases, and nine cases with novel histological findings. Nineteen cases had novel/unusual findings.

This cohort demonstrates how deep fetal phenotypes of some Mendelian disorders can show novel/unusual findings, which have important implications for prenatal diagnosis of these conditions.