We report a patient presenting with neurodevelopmental disorder, cleft palate, micrognathia, relatively mild microcephaly (-2 SD), and ventricular septal defect for whom a 9p terminal deletion was identified by aCGH at birth. The analyses of the samples taken prenatally showed that this terminal deletion resulted from the recombination of a dicentric chromosome which was transmitted to the zygote. Indeed, an inverted duplication with terminal deletion of the short arm of chromosome 9 [invdupdel(9p)] was found in a mosaic state in the placenta. To our knowledge, it is the first reported patient with a terminal deletion present in all tested cells of the blood associated with an invdupdel of the same chromosome in the placenta. This case highlights the role of postzygotic breakages of dicentric chromosomes, a possible underestimated mechanism of formation of terminal deletions. It raises the question of genetic counseling in cases of prenatally detected invdupdels.

The premature fusion of metopic sutures results in the clinical phenotype of trigonocephaly. An association of this characteristic with the monosomy 9p syndrome is well established and the receptor-type protein tyrosine phosphatase gene (PTPRD), located in the 9p24.1p23 region and encoding a major component of the excitatory and inhibitory synaptic organization, is considered as a good candidate to be responsible for this form of craniosynostosis. Moreover PTPRD is known to recruit multiple postsynaptic partners such as IL1RAPL1 which gene alterations lead to non syndromic intellectual disability (ID). We describe a 30 month old boy with severe intellectual disability, trigonocephaly and dysmorphic facial features such as a midface hypoplasia, a flat nose, a depressed nasal bridge, hypertelorism, a long philtrum and a drooping mouth. Microarray chromosomal analysis revealed the presence of a homozygous deletion involving the PTPRD gene, located on chromosome 9p22.3. Reverse Transcription PCR (RT-PCR) amplifications all along the gene failed to amplify the patient's cDNA in fibroblasts, indicating the presence of two null PTPRD alleles. Synaptic PTPRD interacts with IL1RAPL1 which defects have been associated with intellectual disability (ID) and autism spectrum disorder. The absence of the PTPRD transcript leads to a decrease in the expression of IL1RAPL1. These results suggest the direct involvement of PTPRD in ID, which is consistent with the PTPRD -/- mice phenotype. Deletions of PTPRD have been previously suggested as a cause of trigonocephaly in patients with monosomy 9p and genome-wide association study suggested variations in PTPRD are associated with hearing loss. The deletion identified in the reported patient supports previous hypotheses on its function in ID and hearing loss. However, its involvement in the occurrence of metopic synostosis is still to be discussed as more investigation of patients with the 9p monosomy syndrome is required.