Phenotypic homogeneity and genotypic variability in a large series of congenital isolated ACTH-deficiency patients with TPIT gene mutations.

Abstract

Congenital isolated ACTH deficiency (IAD) is a rare disease characterized by low plasma ACTH and cortisol levels and preservation of all other pituitary hormones. This condition was poorly defined before we identified TPIT, a T-box transcription factor with a specific role in differentiation of the corticotroph lineage in mice and humans, as its principal molecular cause. We have enlarged our series of IAD patients to better characterize the phenotype and the genotype of this rare disease. Each exon of the TPIT gene was amplified and sequenced in IAD patients without any identified cause. A functional analysis of each new TPIT mutation was performed. We described the largest series of 91 IAD patients and identified three distinct groups: neonatal onset complete or partial IAD or late onset IAD. We did not identify any TPIT mutation in patients with partial or late-onset IAD. However, we found a TPIT mutation in 65% of patients with neonatal-onset complete IAD. These patients are homozygous or compound heterozygous for TPIT mutations, and their parents are healthy heterozygous carriers. We identified nine new mutations: four missense, one one-nucleotide deletion, three splice-site mutations, and one large deletion. TPIT mutations lead to loss of function by different mechanisms, such as non-sense-mediated mRNA decay, abnormal mRNA splicing, loss of TPIT DNA binding or protein-protein interaction defects. TPIT mutations are responsible for two thirds of neonatal-onset complete IAD but can not be detected in partial or late-onset IAD.