Spondylocostal dysostosis in a pregnancy complicated by confined placental mosaicism for tetrasomy 9p.

The spondylocostal dysostoses (SCD) are a clinically and genetically heterogeneous group of disorders characterized by defects of vertebral segmentation and rib abnormalities. We report on the diagnosis of two siblings with SCD. Diagnosis was first made in a female infant following a pregnancy that was complicated by early fetal hydrops and a nuchal translucency of 8.2 mm in the first trimester. The clinical picture was complicated by the co-existent diagnosis of confined placental mosaicism (CPM) for tetrasomy 9p. To our knowledge, this is the first report of CPM for tetrasomy 9p. Postnatally the diagnosis of SCD was made on the basis of radiographic findings comprising multiple anomalies of the cervical and thoracic vertebrae and multiple fused and dysplastic ribs. Radiographic investigation of other family members showed that the infant's 4-year-old sibling had fusion of four ribs on the right side, indicating a less severe form of SCD. Testing of the genes DLL3, MESP2, and LFNG did not identify a mutation, suggesting that the siblings may have a new molecular subtype of SCD.