Rare mutations of FGFR2 causing apert syndrome: identification of the first partial gene deletion, and an Alu element insertion from a new subfamily

Hum Mutat. 2009 Feb;30(2):204-11. doi: 10.1002/humu.20825.

Abstract

Apert syndrome (AS) is a severe disorder, characterized by craniosynostosis and complex syndactyly of the hands and feet. Two heterozygous gain-of-function substitutions (Ser252Trp and Pro253Arg) in exon IIIa of fibroblast growth factor receptor 2 (FGFR2) are responsible for >98% of cases. Here we describe two novel mutations in FGFR2 in the two patients in whom a mutation had not previously been found in our cohort of 227 AS cases. The first is a 1.93-kb deletion, removing exon IIIc and substantial portions of the flanking introns. This is the first large FGFR2 deletion described in any individual with craniosynostosis. The other mutation is a 5' truncated Alu insertion into exon IIIc. This is the third Alu insertion identified in AS; all have occurred within an interval of only 104 bp, representing an enrichment of over a million-fold compared to the background genomic rate. We show that the inserted Alu element belongs to a small subfamily, not previously known to be mobile, which we term Alu Yk13. Both the deletion and insertion are likely to act by a similar gain-of-function mechanism in which disruption of exon IIIc leads to illegitimate mesenchymal expression of an FGFR2 spliceform containing the alternatively spliced exon IIIb. All the AS-associated Alu insertions have arisen in the paternal germline; we propose that their enrichment in FGFR2 is driven by positive selection of the mutant spermatogonial progenitors, a mechanism analogous to that explaining why the canonical AS nucleotide substitutions also reach exceptionally high levels in sperm.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acrocephalosyndactylia / diagnosis
  • Acrocephalosyndactylia / genetics*
  • Adolescent
  • Adult
  • Alu Elements / genetics*
  • Base Pairing
  • Base Sequence
  • Child, Preschool
  • DNA Mutational Analysis
  • Exons / genetics
  • Fathers
  • Gene Deletion*
  • Genome, Human / genetics
  • Humans
  • Infant
  • Male
  • Molecular Sequence Data
  • Mutagenesis, Insertional / genetics*
  • Receptor, Fibroblast Growth Factor, Type 2 / genetics*

Substances

  • Receptor, Fibroblast Growth Factor, Type 2