Genetic Factors in Birth Defects

Eunice Kennedy Shriver National Institute Of Child Health & Human Development

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Abstract

DNA has been obtained from approximately 20 major malformations for current and future investigations. We have recently expanded our investigations to include searching for copy number variants in rare defects. New York has an exceptionally valuable research resource in having approximately 250,000 births per year from which to identify children with rare defects. In addition to classic candidate gene approaches, cases have been selected for copy number variant studies. Since the last report, a publication has appeared on copy number variants and prune belly syndrome. The etiology of PBS is largely unresolved, but genetic factors are implicated given its recurrence in families. We examined cases of PBS to identify novel pathogenic copy number variants (CNVs). A total of 34 cases (30 males and 4 females) with PBS identified from all live births in New York State (1998-2005) were genotyped using Illumina HumanOmni2.5 microarrays. CNVs were prioritized if they were absent from in-house controls, encompassed 10 consecutive probes, were 20 Kb in size, had 20% overlap with common variants in population reference controls, and had 20% overlap with any variant previously detected in other birth defect phenotypes screened in our laboratory. We identified 17 candidate autosomal CNVs; 10 cases each had one CNV and four cases each had two CNVs. The CNVs included a 158 Kb duplication at 4q22 that overlaps the BMPR1B gene; duplications of different sizes carried by two cases in the intron of STIM1 gene; a 67 Kb duplication 202 Kb downstream of the NOG gene, and a 1.34 Mb deletion including the MYOCD gene. The identified rare CNVs spanned genes involved in mesodermal, muscle, and urinary tract development and differentiation, which might help in elucidating the genetic contribution to PBS. Our work on copy number variants and split hand/foot malformation has also been completed and published. Split hand/foot malformation (SHFM) is a congenital limb deficiency with missing or shortened central digits. Some SHFM genes have been identified but the cause of many SHFM cases is unknown. We used single-nucleotide polymorphism (SNP) microarray analysis to detect copy-number variants (CNVs) in 25 SHFM cases without other birth defects from New York State (NYS), prioritized CNVs absent from population CNV databases, and validated these CNVs using quantitative real-time polymerase chain reaction (qPCR). We tested for the validated CNVs in seven cases from Iowa using qPCR, and also sequenced 36 SHFM candidate genes in all the subjects. Seven NYS cases had a potentially deleterious variant: two had a p.R225H or p.R225L mutation in TP63, one had a 17q25 microdeletion, one had a 10q24 microduplication and three had a 17p13.3 microduplication. In addition, one Iowa case had a de novo 10q24 microduplication. The 17q25 microdeletion has not been reported previously in SHFM and included two SHFM candidate genes (SUMO2 and GRB2), while the 10q24 and 17p13.3 CNVs had breakpoints within genomic regions that contained putative regulatory elements and a limb development gene. In SHFM pathogenesis, the microdeletion may cause haploinsufficiency of SHFM genes and/or deletion of their regulatory regions, and the microduplications could disrupt regulatory elements that control transcription of limb development genes. Our collaboration with the CDC's National Birth Defects Prevention Study and Dr. Paul Romitti at the University of Iowa is currently examining genetic data for associations with choanal atresia, a defect in which the nasal passages fail to develop normally. This study involves testing samples from New York State and from the collaborative group that formed the National Birth Defects Prevention Study. Other defects currently being studied include oral clefts, hypertrophic pyloric stenosis and craniosynostosis. The previous work focused on saggital craniosynostosis. These collaborations expand on this to look for genetic factors associated with defects in other sutures. This work has received external funding and is ongoing. We have established a collaboration with the Statens Serum Institut in Copenhagen, Denmark to examine genetic factors in congenital hydrocephalus. Laboratory analysis is complete and the interpretation of the results has begun. We are beginning a new investigation of sacral agenesis using whole exome sequencing in collaboration with the CDC's National Birth Defects Prevention Study. We will also collaborate with the University of Iowa to examine genetic risk factors in club foot. We are finishing a study with the University of Iowa to examine risk factors in oral cleft cases.