Recherche de mutation rare du trouble bipolaire de type I : étude familiale en Algérie

De nombreuses études ont affirmé l’association significative des Copy Number Variants (CNVs) aux troubles psychotiques et de l’humeur, remettant en question l’hypothèse « maladie commune-variants communs » pour un modèle « maladie commune-variants rares » [1]. Par ailleurs, plusieurs études ont montré l’association de même CNVs à des pathologies différentes telles que l’autisme, le trouble bipolaire, le retard mental ou l’épilepsie, ce qui suggère un effet pléiotropique de ces mutations qui pourrait conduire à reconsidérer la nosologie actuelle. Enfin, certains de ces CNVs apparaîtraient de novo, mais il existe peu d’études familiales, et aucune effectuée sur des pedigrees étendus pour préciser les relations génotype-phénotype au sein des familles [2]. Dans ce travail nous avons étudié une famille consanguine multi-générationnelle et multiplexe pour le phénotype de trouble bipolaire de type I et de schizophrénie ; identifiée dans la région de Tlemcen au nord ouest de l’Algérie. Une recherche pangénomique de CNVs utilisant le Kit 44 K Agilent Human Genome CGH Microarray, a été achevée pour quatre sujets dont deux atteints et deux sains. Cette analyse a permis de mettre en évidence la duplication 16p13.33 en position 3863532-3927262 (Hg19), qui présente un caractère de novo chez une patiente, car absente chez ses deux parents. La duplication de la région chromosomique 16p13.3 affectant le gène CREBBP dont la délétion et/ou la mutation est incriminée dans le syndrome de Rubinstein-Taybi est actuellement décrite dans une entité syndromique regroupant dysmorphie de la face, retard mental léger à moyen, croissance normale, arthrogrypose, anomalies orthopédiques des extrémités surtout des mains et des anomalies de développement cardiaque, génital et oculaire [3]. Ce CNV n’a jamais été décrit précédemment dans le phénotype de trouble bipolaire ; dans ce travail nous présentons une nouvelle description génotype-phénotype d’une dup16p13.33 de novo, dans le trouble bipolaire type I.

Molecular mechanisms generating and stabilizing terminal 22q13 deletions in 44 subjects with Phelan/McDermid syndrome

In this study, we used deletions at 22q13, which represent a substantial source of human pathology (Phelan/McDermid syndrome), as a model for investigating the molecular mechanisms of terminal deletions that are currently poorly understood. We characterized at the molecular level the genomic rearrangement in 44 unrelated patients with 22q13 monosomy resulting from simple terminal deletions (72%), ring chromosomes (14%), and unbalanced translocations (7%). We also discovered interstitial deletions between 17-74 kb in 9% of the patients. Haploinsufficiency of the SHANK3 gene, confirmed in all rearrangements, is very likely the cause of the major neurological features associated with PMS. SHANK3 mutations can also result in language and/or social interaction disabilities. We determined the breakpoint junctions in 29 cases, providing a realistic snapshot of the variety of mechanisms driving non-recurrent deletion and repair at chromosome ends. De novo telomere synthesis and telomere capture are used to repair terminal deletions; non-homologous end-joining or microhomology-mediated break-induced replication is probably involved in ring 22 formation and translocations; non-homologous end-joining and fork stalling and template switching prevail in cases with interstitial 22q13.3. For the first time, we also demonstrated that distinct stabilizing events of the same terminal deletion can occur in different early embryonic cells, proving that terminal deletions can be repaired by multistep healing events and supporting the recent hypothesis that rare pathogenic germline rearrangements may have mitotic origin. Finally, the progressive clinical deterioration observed throughout the longitudinal medical history of three subjects over forty years supports the hypothesis of a role for SHANK3 haploinsufficiency in neurological deterioration, in addition to its involvement in the neurobehavioral phenotype of PMS.

Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes

BACKGROUND

Duplications and deletions in the human genome can cause disease or predispose persons to disease. Advances in technologies to detect these changes allow for the routine identification of submicroscopic imbalances in large numbers of patients.

METHODS

We tested for the presence of microdeletions and microduplications at a specific region of chromosome 1q21.1 in two groups of patients with unexplained mental retardation, autism, or congenital anomalies and in unaffected persons.

RESULTS

We identified 25 persons with a recurrent 1.35-Mb deletion within 1q21.1 from screening 5218 patients. The microdeletions had arisen de novo in eight patients, were inherited from a mildly affected parent in three patients, were inherited from an apparently unaffected parent in six patients, and were of unknown inheritance in eight patients. The deletion was absent in a series of 4737 control persons (P=1.1x10(-7)). We found considerable variability in the level of phenotypic expression of the microdeletion; phenotypes included mild-to-moderate mental retardation, microcephaly, cardiac abnormalities, and cataracts. The reciprocal duplication was enriched in nine children with mental retardation or autism spectrum disorder and other variable features (P=0.02). We identified three deletions and three duplications of the 1q21.1 region in an independent sample of 788 patients with mental retardation and congenital anomalies.

CONCLUSIONS

We have identified recurrent molecular lesions that elude syndromic classification and whose disease manifestations must be considered in a broader context of development as opposed to being assigned to a specific disease. Clinical diagnosis in patients with these lesions may be most readily achieved on the basis of genotype rather than phenotype.

Islands of euchromatin-like sequence and expressed polymorphic sequences within the short arm of human chromosome 21

The goals of the human genome project did not include sequencing of the heterochromatic regions. We describe here an initial sequence of 1.1 Mb of the short arm of human chromosome 21 (HSA21p), estimated to be 10% of 21p. This region contains extensive euchromatic-like sequence and includes on average one transcript every 100 kb. These transcripts show multiple inter- and intrachromosomal copies, and extensive copy number and sequence variability. The sequencing of the "heterochromatic" regions of the human genome is likely to reveal many additional functional elements and provide important evolutionary information.