The genomic landscape of balanced cytogenetic abnormalities associated with human congenital anomalies

Despite the clinical significance of balanced chromosomal abnormalities (BCAs), their characterization has largely been restricted to cytogenetic resolution. We explored the landscape of BCAs at nucleotide resolution in 273 subjects with a spectrum of congenital anomalies. Whole-genome sequencing revised 93% of karyotypes and demonstrated complexity that was cryptic to karyotyping in 21% of BCAs, highlighting the limitations of conventional cytogenetic approaches. At least 33.9% of BCAs resulted in gene disruption that likely contributed to the developmental phenotype, 5.2% were associated with pathogenic genomic imbalances, and 7.3% disrupted topologically associated domains (TADs) encompassing known syndromic loci. Remarkably, BCA breakpoints in eight subjects altered a single TAD encompassing MEF2C, a known driver of 5q14.3 microdeletion syndrome, resulting in decreased MEF2C expression. We propose that sequence-level resolution dramatically improves prediction of clinical outcomes for balanced rearrangements and provides insight into new pathogenic mechanisms, such as altered regulation due to changes in chromosome topology

Disruption of a Novel Gene (IMMP2L) by a Breakpoint in 7q31 Associated with Tourette Syndrome

Gilles de la Tourette syndrome (GTS) is a complex neuropsychiatric disorder characterized by multiple motor and phonic tics. We identified a male patient with GTS and other anomalies. It was determined that he carried a de novo duplication of the long arm of chromosome 7 [46,XY,dup(7)(q22.1-q31.1)]. Further molecular analysis revealed that the duplication was inverted. The distal chromosomal breakpoint occurred between the two genetic markers D7S515 and D7S522, which define a region previously shown to be disrupted in a familiar case of GTS. Yeast and bacterial artificial chromosome clones spanning the breakpoints were identified by means of FISH analysis. To further characterize the distal breakpoint for a role in GTS, we performed Southern blot hybridization analysis and identified a 6.5-kb SacI junction fragment in the patient’s genomic DNA. The DNA sequence of this fragment revealed two different breaks in 7q31 within a region of ∼500 kb. IMMP2L, a novel gene coding for the apparent human homologue of the yeast mitochondrial inner membrane peptidase subunit 2, was found to be disrupted by both the breakpoint in the duplicated fragment and the insertion site in 7q31. The cDNA of the human IMMP2L gene was cloned, and analysis of the complete 1,522-bp transcript revealed that it encompassed six exons spanning 860 kb. The possible role of IMMP2L and several other candidate genes within the region of chromosomal rearrangement, including NRCAM, Leu-Rch Rep, and Reelin, is discussed. The 7q31 breakpoint interval has also been implicated in other neuropsychiatric diseases that demonstrate some clinical overlap with GTS, including autism and speech-language disorder

A new bacteriophage P1-derived vector for the propagation of large human DNA fragments

We have designed a P1 vector (pCYPAC−1) for the introduction of recombinant DNA into E. coli using electroporation procedures. The new cloning system, P1−derived arteficial chromosomes (PACs), was used to establish an initial 15,000 clone library with an average insert size of 130−150 kilobase pairs (kb). No chimaerism has been observed in 34 clones, by fluorescence in situ hybridization. Similarly, no insert instability has been observed after extended culturing, for 20 clones. We conclude that the PAC cloning system will be useful in the mapping and detailed analysis of complex genomes

Metopic and sagittal synostosis in Greig cephalopolysyndactyly syndrome: five cases with intragenic mutations or complete deletions of GLI3

Greig cephalopolysyndactyly syndrome (GCPS) is a multiple congenital malformation characterised by limb and craniofacial anomalies, caused by heterozygous mutation or deletion of GLI3. We report four boys and a girl who were presented with trigonocephaly due to metopic synostosis, in association with pre- and post-axial polydactyly and cutaneous syndactyly of hands and feet. Two cases had additional sagittal synostosis. None had a family history of similar features. In all five children, the diagnosis of GCPS was confirmed by molecular analysis of GLI3 (two had intragenic mutations and three had complete gene deletions detected on array comparative genomic hybridisation), thus highlighting the importance of trigonocephaly or overt metopic or sagittal synostosis as a distinct presenting feature of GCPS. These observations confirm and extend a recently proposed association of intragenic GLI3 mutations with metopic synostosis; moreover, the three individuals with complete deletion of GLI3 were previously considered to have Carpenter syndrome, highlighting an important source of diagnostic confusion