Mutation Analysis of the FOXF1 Gene
Two lines of evidence suggested that FOXF1 haploinsufficiency might be responsible for ACD/MPV in our initial cohort. First, patients with deletions harboring FOXF1 (D1–D6) had a severe respiratory phenotype (confirmed histologically as ACD/MPV in three cases), whereas a patient with a deletion harboring FOXC2 and FOXL1 but not FOXF1, patient D7, did not. Second, mice haploinsufficient for Foxf1 have abnormal alveolar development, notwithstanding the fact that the histological changes are not identical to those of ACD/MPV.18,19 We therefore sequenced FOXF1 in a cohort of 18 patients with ACD/MPV and other malformations.10 We identified four de novo heterozygous mutations in the coding sequence of FOXF1 in four unrelated patients with sporadic ACD/MPV. Patient M1 had a nonsense mutation (c.150C→A; p.Y50X) in exon 1; patient M2 had a frameshift mutation (c.775dupT; p.Y259Lfs11X) in exon 1; patient M3 had a frameshift mutation (c.956_957delTT; p.F319CfsX66) in exon 2 adding 29 amino acids to the protein, as predicted by conceptual translation; and patient M4 had a T→C substitution in the first base of the stop codon, a no-stop mutation (c.1063T→C; p.X355RextX74) adding 73 amino acids to the protein, as predicted by conceptual translation (Figures 3A–3D). All four patients had associated malformations, including a partial atrioventricular canal defect (1/4 cases), patent ductus arteriosus (1/4), bowel malrotation (3/4), a congenital short bowel (1/4), an annular pancreas (1/4), and urinary tract malformations (3/4) (Table 2).