Differences in DNA methylation status explain phenotypic variability in patients with 5p- syndrome.

Cri Du Chat syndrome, or 5p- syndrome, is characterized by a terminal or interstitial deletion on the short arm of chromosome 5 that causes variable clinical manifestations, including high-pitched cry in newborns, delayed growth, and global development. Different cytogenomic rearrangements, family history, and environmental factors may hinder the genotype-phenotype association. Thus, the phenotypic variability of this syndrome may not be limited only to variations in gene structure, such as deletions and duplications. It is possible that other mechanisms related to the activation or inactivation of promoters and/or exons of actively transcribed genes, such as DNA methylation are involved. Therefore, we studied the genome-wide methylation status profile of peripheral blood samples from fifteen patients with Cri du Chat Syndrome and nine control samples through the array method to look for Differentially Methylated Regions. We found that Differentially Methylated Regions outside the 5p region are mainly associated with regulating gene transcription, splicing, and chromatin remodeling. Most biological pathways are related to transcription, histone and chromatin binding, spliceosome and ribosomal complex, and RNA processing. Our results suggest that changes in the 5p region can cause an imbalance in other chromosomal regions capable of affecting gene modulation and thus explain the phenotypic differences in patients with 5p-.

Cri-du-Chat Syndrome: Revealing a Familial Atypical Deletion in 5p.

Introduction: Cri-du-chat syndrome is generally diagnosed when patients present a high-pitched cry at birth, microcephaly, ocular hypertelorism, and prominent nasal bridge. The karyotype is useful to confirm deletions in the short arm of chromosome 5 (5p-) greater than 10 Mb. In cases of smaller deletions, it is necessary to resort to other molecular techniques such as fluorescence in situ hybridization, multiplex ligation-dependent probe amplification (MLPA) or genomic array. Case Presentation: We report a family with an atypical deletion in 5p (mother and 2 children) and variable phenotypes compared with the literature. We applied a P064 MLPA kit to evaluate 5p- in the mother and the 2 children, and we used the Infinium CytoSNP-850K BeadChip genomic array to evaluate the siblings, an 11-year-old boy and a 13-year-old girl, to better define the 5p breakpoints. Both children presented a high-pitched cry at birth, but they did not present any of the typical physical features of 5p- syndrome. The MLPA technique with 5 probes for the 5p region revealed that the patients and their mother presented an atypical deletion with only 4 probes deleted (TERT_ex2, TERT_ex13, CLPTM1L, and IRX4). The genomic array performed in the siblings' samples revealed a 6.2-Mb terminal deletion in 5p15.33p15.32, which was likely inherited from their mother, who presented similar molecular features, seen in MLPA. Discussion: The sparing of the CTNND2 gene, which is associated with cerebral development, in both siblings may explain why these 2 patients had features such as better communication skills which most patients with larger 5p deletions usually do not present. In addition, both patients had smaller deletions than those found in patients with a typical 5p- phenotype. This report demonstrates the utility of genomic arrays as a diagnostic tool to better characterize atypical deletions in known syndromes such as 5p- syndrome, which will allow a better understanding of the genotype-phenotype correlations.