Aberrant SP-B mRNA in lung tissue of patients with congenital alveolar proteinosis (CAP)

Mutations in the surfactant protein (SP)‐B gene are responsible for SP‐B deficiency in congenital alveolar proteinosis (CAP) (Nogee et al. J Clin Invest 1994: 93: 1860–1883; Lin et al. Mol Genet Metab 1998: 64: 25–35; Klein et al. Pediatrics 1998: 132: 244–248; Ballard et al. Pediatrics 1995: 96: 1046–1052). The multigenerational consanguineous pedigree under study does not carry any of the known mutations, although this pedigree had 14 infant deaths following respiratory distress at birth. Immunostaining of the lungs from three such infants revealed decreased or absent SP‐B. By sequencing of SP‐B exons, exon–intron junctions, and the 5′ and 3′ flanking regions, nine polymorphisms were found in this pedigree, but none of them could explain the observed SP‐B deficiency. Further analysis of SP‐B mRNA by reverse transcription‐polymerase chain reaction from paraffin‐embedded lung tissue of CAP patients showed that SP‐B mRNA is not intact. Although the sequence of mRNA from exon 1–exon 7 and from exon 8–exon 10 could be amplified, the region between exons 7 and 8 could not. From fluorescence in situ hybridization of the short arm of chromosome 2p, only 2 signals were identified, eliminating the possibility of translocation as the cause of the SP‐B mRNA aberrance. Although the nature of the genetic basis of SP‐B deficiency in this family is currently unknown, the existence of aberrant SP‐B mRNA may, at least in part, be responsible for the SP‐B deficiency in this pedigree.