Partial trisomy 9p is one of the most common detected autosomal structural anomalies, so the phenotype-genotype correlation of this rearrangement has been well described. Despite variation in size of the 9p duplications, trisomy 9p syndrome is characterized by typical dysmorphic features and a variable but constant psychomotor and mental retardation. Previously reported phenotype genotype correlation studies proposed that the critical region for phenotype is located in 9p22. We report here on a new patient with partial trisomy 9p13.3→9pter in an 8-year-old boy with typical trisomy 9p dysmorphic features but a normal mental development. Cytogenetics investigations showed that our patient karyotype was 47,XY,+ der(22)t(9;22)(p13.q11) inherited by a 3:1 disjunction of a maternal reciprocal translocation t(9;22)(p13.q11). FISH and array CGH analysis were used to better characterize duplicated chromosomal regions and showed a large duplication of chromosome 9p13.3→9pter associated to microduplication in 22q11.1. The size of the duplications in chromosomes 9p and 22q were estimated about 33.9 and 2.67 Mb, respectively. The comparison between this case and those reported in the literature allows us to support that all syndromes show variability and that not all partial trisomies 9p are associated with intellectual disability.

Background: Lissencephaly represents a rare subgroup of genetically distinct neurological disorders of neuronal migration characterized by a paucity or absence of cerebral gyration. The most common form of lissencephaly has been isolated and referred to as classic or type 1 lissencephaly. It is frequently related to abnormalities within LIS1 or DCX genes, with abnormalities ranging from single base pair substitutions to contiguous gene deletions. Methods: In this study, we report, for the first time, a clinical and genetic characterization of eight unrelated Tunisian children presenting type 1 lissencephaly. We screened LIS1 and DCX abnormalities thanks to a combination of molecular cytogenetic methods and next generation sequencing. Results: One deletion of DCX and three deletions of LIS1 were observed. One of these deletions was inherited from a maternal reciprocal translocation and estimated to approximately 2,9 Mb length. In addition, a 26 Kb LIS1 deletion was detected and refined between exon 3 up to exon 11 by target capture and sequencing. The last LIS1 rearrangement was a mutation (c.779T>A, p.V260E). Finally, two novel DCX mutations were found out (c.910G>C, p.G304R/c.436T>C, p.F146L). Conclusions: Our data confirm the individuality and originality of type 1 lissencephaly on both the phenotypic and the genetic levels. Furthermore, our data confirm again that LIS1 and DCX are the most genes associated with type 1 lissencephaly and spotlight the usefulness of developing approaches and methods for detecting a large number of known causative gene mutations.