title: Duplications of BHLHA9 are associated with ectrodactyly and tibia hemimelia inherited in non-Mendelian fashion.
abstract: BACKGROUND
  Split-hand/foot malformation (SHFM)-also known as ectrodactyly-is a congenital disorder characterised by severe malformations of the distal limbs affecting the central rays of hands and/or feet. A distinct entity termed SHFLD presents with SHFM and long bone deficiency. Mouse models suggest that a defect of the central apical ectodermal ridge leads to the phenotype. Although six different loci/mutations (SHFM1-6) have been associated with SHFM, the underlying cause in a large number of cases is still unresolved.
  
  
  METHODS
  High resolution array comparative genomic hybridisation (CGH) was performed in patients with SHFLD to detect copy number changes. Candidate genes were further evaluated for expression and function during limb development by whole mount in situ hybridisation and morpholino knock-down experiments.
  
  
  RESULTS
  Array CGH showed microduplications on chromosome 17p13.3, a locus previously associated with SHFLD. Detailed analysis of 17 families revealed that this copy number variation serves as a susceptibility factor for a highly variable phenotype with reduced penetrance, particularly in females. Compared to other known causes for SHFLD 17p duplications appear to be the most frequent cause of SHFLD. A ~11.8 kb minimal critical region was identified encompassing a single gene, BHLHA9, a putative basic loop helix transcription factor. Whole mount in situ hybridisation showed expression restricted to the limb bud mesenchyme underlying the apical ectodermal ridge in mouse and zebrafish embryos. Knock down of bhlha9 in zebrafish resulted in shortening of the pectoral fins.
  
  
  CONCLUSIONS
  Genomic duplications encompassing BHLHA9 are associated with SHFLD and non-Mendelian inheritance characterised by a high degree of non-penetrance with sex bias. Knock-down of bhlha9 in zebrafish causes severe reduction defects of the pectoral fin, indicating a role for this gene in limb development.
authors.affiliation: Institute for Medical Genetics and Human Genetics, Charité-Universitätsmedizin Berlin, Berlin, Germany. eva.klopocki@charite.de
authors.forename: Eva
authors.initials: E
authors.lastname: Klopocki
authors.forename: Silke
authors.initials: S
authors.lastname: Lohan
authors.forename: Sandra C
authors.initials: SC
authors.lastname: Doelken
authors.forename: Sigmar
authors.initials: S
authors.lastname: Stricker
authors.forename: Charlotte W
authors.initials: CW
authors.lastname: Ockeloen
authors.forename: Renata
authors.initials: R
authors.lastname: Soares Thiele de Aguiar
authors.forename: Karina
authors.initials: K
authors.lastname: Lezirovitz
authors.forename: Regina Celia
authors.initials: RC
authors.lastname: Mingroni Netto
authors.forename: Aleksander
authors.initials: A
authors.lastname: Jamsheer
authors.forename: Hitesh
authors.initials: H
authors.lastname: Shah
authors.forename: Ingo
authors.initials: I
authors.lastname: Kurth
authors.forename: Rolf
authors.initials: R
authors.lastname: Habenicht
authors.forename: Matthew
authors.initials: M
authors.lastname: Warman
authors.forename: Koenraad
authors.initials: K
authors.lastname: Devriendt
authors.forename: Ulrike
authors.initials: U
authors.lastname: Kordass
authors.forename: Maja
authors.initials: M
authors.lastname: Hempel
authors.forename: Anna
authors.initials: A
authors.lastname: Rajab
authors.forename: Outi
authors.initials: O
authors.lastname: Mäkitie
authors.forename: Mohammed
authors.initials: M
authors.lastname: Naveed
authors.forename: Uppala
authors.initials: U
authors.lastname: Radhakrishna
authors.forename: Stylianos E
authors.initials: SE
authors.lastname: Antonarakis
authors.forename: Denise
authors.initials: D
authors.lastname: Horn
authors.forename: Stefan
authors.initials: S
authors.lastname: Mundlos
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics*; D004480:Ectromelia / Q000235:genetics*; D005260:Female; D005385:Fingers / Q000002:abnormalities; D020440:Gene Duplication; D055785:Gene Knockdown Techniques; D056726:Genetic Association Studies; D005838:Genotype; D006228:Hand Deformities, Congenital / Q000235:genetics*; D006801:Humans; D040582:Inheritance Patterns; D017880:Limb Deformities, Congenital / Q000235:genetics; D008297:Male; D010375:Pedigree; D010641:Phenotype; D013977:Tibia / Q000002:abnormalities*; D015027:Zebrafish / Q000196:embryology / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; C571985:BHLHA9 protein, human