Monoallelic expression of normal mRNA in the PIT1 mutation heterozygotes with normal phenotype and biallelic expression in the abnormal phenotype.

The combined deficiency of thyrotropin, growth hormone and prolactin, caused by PIT1 abnormality manifests in the homozygous or heterozygous state. We studied a patient having an allele with Arg271Trp mutation, which produces clinical symptoms in heterozygotes by a dominant-negative effect. However, in the family, her father, grandmother and aunts had the same mutation without clinical symptoms, although the proband had typical phenotypic expression. We analyzed the PIT1 transcript in peripheral lymphocytes by reverse transcription-polymerase chain reaction and found monoallelic expression of normal allele in the father and grandmother and skewed pattern of biallelic expression in the proband. The phenotypic expression of PIT1 abnormality may depend on different transcription of the PIT1 gene.