Pituitary stalk interruption and ectopic posterior lobe on magnetic resonance imaging (MRI) are frequently observed in patients with GH deficiency (GHD), but their pathogenesis remains controversial. We performed pituitary stimulation tests, MRI, and studied GH-1, GHRH receptor (GHRH-R), and Prophet of Pit-1 (PROP-1) genes in 76 patients with GHD. Of 33 patients with isolated GHD, 4 had GH-1 deletions and 4 had GHRH-R mutations; of 43 patients with combined pituitary hormone deficiency, 1 had PIT-1 and 5 had PROP-1 mutations. Compared with the 62 patients without mutations, 14 patients with mutations had higher frequency of consanguinity (57 vs. 2%, P < 0.001), familial cases (21 vs. 3%, P < 0.05), and lower frequency of breech delivery or hypoxemia at birth (0 vs. 39%, P < 0.005). On MRI, all patients with mutations had an intact stalk, whereas it was interrupted or thin in 74% without mutations (P < 0.001). The posterior pituitary lobe was in normal position in 92% of patients with mutations against 13% without mutations (P < 0.001). Among patients with combined pituitary hormone deficiency, hormonal deficiencies were of pituitary origin in all with PROP-1 and PIT-1 mutations and suggestive of hypothalamic origin in 81% without mutations. Perinatal insults were associated with thin/interrupted pituitary stalk, ectopic posterior lobe, and hypothalamic origin of hormonal deficiencies. In contrast, GH-1, GHRH-R, and PROP-1 mutations were associated with consanguineous parents, intact pituitary stalk, normal posterior lobe, and pituitary origin of hormonal deficiencies. We conclude that pituitary MRI and hormonal response to stimulation tests are useful in selection of patients and candidate genes to elucidate the etiological diagnosis of GHD.

Objective: To establish the cut-off values of GH measured by immunofluorometric assay, a more sensitive and specific assay, in normal prepubertal children and compare their values with those of proven GH-deficient patients. Methods: 30 normal children (20 males) and 26 patients with known causes of GH deficiency were submitted to the clonidine test and their GH values were compared. A powdered clonidine tablet (0.1 mg/m²) was given orally and blood samples for GH measurements were drawn at times –30, 0, 60, 90 and 120 min. Results: GH peak values presented a wide variation ranging from 1.7 to 25 µg/l (mean ± SD = 12.87 ± 5.8 µg/l) in the normal group. The cut-off values for the 5th and 10th percentiles of the distribution curve were 3.3 and 5.5 µg/l, respectively. In the GH deficiency group, maximum GH levels after clonidine stimulation ranged from <0.1 to 2.1 µg/l (0.56 ± 0.58 µg/l). Conclusions: The cut-off values obtained with the immunofluorometric method are lower than the ones obtained by radioimmunoassay. We suggest a cut-off value of 3.3 µg/l (5th percentile) that ensures 100% of sensitivity along with 93% of specificity to exclude the diagnosis of GH deficiency when using this immunofluorometric method.

Mutations in the pituitary-specific paired-like homeodomain transcription factor, PROP-1, result in combined pituitary hormone deficiency. We studied a Brazilian girl, offspring of first cousins, who presented with short stature and deficiencies of GH, TSH, PRL, LH, and FSH. Her cortisol response to hypoglycemia was determined at age 4.9, 10.7, and 14.1 yr and remained normal. Magnetic resonance imaging at the age of 9 yr revealed an anterior pituitary lobe of diminished height (3 mm; normal, 4.5 +/- 0.6), but radiography revealed a sella turcica volume above the normal mean. Direct sequencing of the PROP-1 gene revealed homozygosity for a novel 263T>C transition that results in the replacement of a highly conserved phenylalanine by serine at codon 88 (F88S). F88 constitutes the hydrophobic core of the first helix of the homeodomain of PROP-1, and the substitution by the polar residue serine is expected to alter the secondary structure and impair binding of the mutated PROP-1 to DNA target sequences. The F88S mutation (which corresponds to murine F85S) was introduced into the murine Prop-1 complementary DNA and its consequences on DNA binding and trans-activation were assessed in vitro. In contrast to wild-type Prop-1, the F88S mutant showed no significant DNA binding to a PRDQ9 Prop-1 response element in gel shift assays. Transcriptional activation of a luciferase reporter gene containing a PRDQ9 site upstream of a simian virus 40 promoter was reduced to approximately 34% compared with that of wild-type Prop-1 in transiently transfected TSA-201 human embryonic kidney cells. The F88S mutation further expands the repertoire of mutations in PROP-1.

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