MONOALLELIC EXPRESSION OF NORMAL MESSENGER-RNA 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-negat ive 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 react ion and found monoallelic expression of normal allele in the father an d grandmother and skewed pattern of biallelic expression in the proban d. The phenotypic expression of PIT1 abnormality may depend on differe nt transcription of the PIT1 gene.