Characterization of a noncontiguous gene deletion of the growth hormone receptor in Laron's syndrome.

Abstract

Noncontiguous deletion of the GH receptor (GHR) gene has been described as a molecular defect causing Laron's syndrome (LS). The abnormal allele (GHR Del-3,5,6) lacks exons 3, 5, and 6. Exon 4 is retained on variant-sized restriction fragments. We studied DNA from 10 additional LS subjects of Jewish-oriental origin and found this allele in 3 samples. All subjects with this complex deletion allele were from Iran or Iraq and were not clinically distinguishable from other individuals with LS. Multiple restriction enzyme digests and Southern blotting with GHR exon 4-specific probes demonstrated that the allele retains genomic material for at least 9.8 kilobases 5' and 1.8 kilobases 3' to exon 4. Reverse transcription of mRNA, polymerase chain reaction amplification, and cDNA sequencing showed that exon 4 is syntenic and colinear with the other GHR exons. Normal splice sites were used, but the predicted protein was severely truncated due to a frameshift and a premature stop codon in exon 7. The premature stop codon terminated the protein after amino acid 53 and led to loss of the transmembrane and intracellular portions of the receptor. This mutant GHR gene results clinically in severe GH insensitivity.