Fetal phenotypes of Mendelian disorders: A descriptive study from India.

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Fetal presentation of chondrodysplasia with joint dislocations, GPAPP type, caused by novel biallelic IMPAD1 variants.

Biallelic IMPAD1 pathogenic variants leads to deficiency of GPAPP (Golgi 3-prime phosphoadenosine 5-prime phosphate 3-prime phosphatase) protein and clinically causes chondrodysplasia, which is characterized by short stature with short limbs, craniofacial malformations, cleft palate, hand and foot anomalies, and various radiographic skeletal manifestations. Here we describe prenatal presentation of GPAPP deficiency caused by novel biallelic pathogenic variants, 2 base pair duplication in exon 2 of IMAPD1 gene in a patient of Asian-Indian origin. Further we report on diagnostic clues of prenatal presentation of GPAPP deficiency through ultrasonography, fetal MRI, and postmortem findings. We also provide evidence of pathophysiology of underlying GPAPP deficiency in the form of disorganization and dysplastic chondrocytes and reduced sulfation of glycoproteins through histopathology of cartilage similar to that described in mice IMPAD1 homozygous mutant model.