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Mutations in the coding region of the TWIST gene (encoding a basic helix-loop-helix transcription factor) have been identified in some cases of Saethre-Chotzen syndrome. Haploinsufficiency appears to be the pathogenic mechanism involved. To investigate the possibility that complete deletions of the TWIST gene also contribute to this disorder, we have developed a comprehensive strategy to screen for coding-region mutations and for complete gene deletions. Heterozygous TWIST mutations were identified in 8 of 10 patients with Saethre-Chotzen syndrome and in 2 of 43 craniosynostosis patients with no clear diagnosis. In addition to six coding-region mutations, our strategy revealed four complete TWIST deletions, only one of which associated with a translocation was suspected on the basis of conventional cytogenetic analysis. This case and two interstitial deletions were detectable by analysis of polymorphic microsatellite loci, including a novel (CA)n locus 7.9 kb away from TWIST, combined with FISH; these deletions ranged in size from 3.5 Mb to >11.6 Mb. The remaining, much smaller deletion was detected by Southern blot analysis and removed 2,924 bp, with a 2-bp orphan sequence at the breakpoint. Significant learning difficulties were present in the three patients with megabase-sized deletions, which suggests that haploinsufficiency of genes neighboring TWIST contributes to developmental delay. Our results identify a new microdeletion disorder that maps to chromosome band 7p21.1 and that causes a significant proportion of Saethre-Chotzen syndrome.

Original publication

DOI

10.1086/302122

Type

Journal article

Journal

Am J Hum Genet

Publication Date

11/1998

Volume

63

Pages

1282 - 1293

Keywords

Acrocephalosyndactylia, Chromosome Banding, Chromosome Mapping, Chromosomes, Human, Pair 7, Craniosynostoses, DNA Primers, Female, Genetic Markers, Helix-Loop-Helix Motifs, Humans, Karyotyping, Male, Mass Screening, Molecular Sequence Data, Nuclear Proteins, Polymerase Chain Reaction, Sequence Deletion, Transcription Factors, Twist-Related Protein 1