Heike Stobbe

Functional Characterization of a Heterozygous GLI2 Missense Mutation in Patients With Multiple Pituitary Hormone Deficiency

CONTEXT The GLI2 transcription factor is a major effector protein of the sonic hedgehog pathway and suggested to play a key role in pituitary development. Genomic GLI2 aberrations that mainly result in truncated proteins have been reported to cause holoprosencephaly or holoprosencephaly-like features, sometimes associated with hypopituitarism. OBJECTIVE Our objective was to determine the frequency of GLI2 mutations in patients with multiple pituitary hormone deficiency (MPHD). DESIGN Patients were selected from participants in the Genetics and Neuroendocrinology of Short Stature International Study (GeNeSIS) program. Patients with mutations within established candidate genes were excluded. PATIENTS A total of 165 patients with MPHD defined as GH deficiency and at least 1 additional pituitary hormone deficiency were studied regardless of the presence of extrapituitary clinical manifestations. MAIN OUTCOME MEASURES Prevalence of GLI2 variations in MPHD patients was assessed and detailed phenotypic characterization is given. Transcriptional activity of identified GLI2 variants was evaluated by functional reporter assays. RESULTS In 5 subjects, 4 heterozygous missense variants were identified, of which 2 are unpublished so far. One variant, p.R516P, results in vitro in a complete loss of protein function. In addition to GH deficiency, the carrier of the mutation demonstrates deficiency of thyrotrope and gonadotrope function, a maldescended posterior pituitary lobe, and polydactyly, but no midline defects. CONCLUSIONS For the first time, we show that heterozygous amino acid substitutions within GLI2 may lead to MPHD with mild extrapituitary findings. The phenotype of GLI2 mutations is variable, and penetrance is incomplete. GLI2 mutations are associated with anterior pituitary hypoplasia, and frequently, ectopy of the posterior lobe occurs.

A novel homozygous HESX1 mutation causes panhypopituitarism without midline defects and optic nerve anomalies.

Abstract Objective: There are many genes reported to have been associated with combined pituitary hormone deficiencies, but mutations in HESX1strongly correlate with septo-optic dysplasia. Our aim was to determine the cause of panhypopituitarism in our patient. Patients and methods: We studied an 8-month-old child having panhypopituitarism. The coding exons of PIT1, PROP1, LHX3, and HESX1 genes were amplified. Direct sequencing was done after denaturing HLPC. Results: We identified a novel homozygous mutation (R160H) within the homeodomain of HESX1, which, to our knowledge, is the first to be described in humans. Neuroimaging studies revealed anterior pituitary aplasia, a normal posterior pituitary gland, and a thin pituitary stalk but no midline abnormalities. Optic nerve studies showed no pathology. This mutation is also carried in the parents of the affected child in a heterozygous pattern, suggesting an autosomal recessive inheritance. Conclusion: These data demonstrate that homozygous HESX1 mutation causing an R160H substitution can result in panhypopituitarism without midline defects.

Novel heterozygous IGF1R mutation in two brothers with developing impaired glucose tolerance.

Abstract Infants born small for gestational age (SGA) are at risk to develop metabolic complications. Insulin-like growth factor 1 (IGF-1) resistance due to IGF-1 receptor (IGF1R) mutations is a rare genetic condition that causes proportionate growth retardation. The contribution of an impaired IGF1R function to the development of comorbidities such as disturbed glucose homeostasis is not well understood. Genetic analysis and detailed auxological, endocrine and psychological investigations in two male SGA siblings were performed. The two patients and their father bear a novel heterozygous mutation (p.Cys1248Tyr) in the IGF1R gene. Both brothers displayed very similar growth pattern before and during recombinant human growth hormone treatment, whereas oral glucose tolerance tests showed variable manifestations of progressive impaired glucose tolerance. The father had already developed type 2 diabetes mellitus. Growth retardation in our patients is likely caused by the IGF1R mutation that might predispose to disturbances of carbohydrate homeostasis. Therefore, a close metabolic monitoring of affected patients is indicated, particularly if growth hormone therapy is commenced.

A Novel GH1 Mutation in a Family with Isolated Growth Hormone Deficiency Type II

Background: Four distinct familial types of isolated GH deficiency (IGHD) have been described so far. Objective: We report a novel nonsense GH1 mutation in a father and a son. Patients: Father’s height was 137.3 cm (–6.79 SDS); mother’s height was 157.3 cm (–1.86 SDS). By the age of 8.25 years, his height was 104.3 cm (–4.82 SDS) and his weight was 18.3 kg (–3.35 SDS). GH stimulation tests had low peak GH value of 6.5 ng/ml (proband) and 6.3 ng/ml (father). Other pituitary hormones and magnetic resonance imaging (MRI) of the pituitary region was normal in both patients. The proband received recombinant human GH (rhGH) treatment (30 µg/kg/day) and he grew 15.4 cm in 15 months. Results: Sequencing of the GH1 gene revealed a novel heterozygous nonsense mutation in both the father and the son (c.199A>T), which introduces a stop codon in exon 3. Conclusion: We present a family with IGHD II, with severe short stature, no phenotypic characteristics of GHD and a novel nonsense mutation in exon 3 of the GH1 gene. As fibroblasts were unavailable, we used computer analysis and we propose a unique mechanism that combines aberrant splicing and derogated GH release from the pituitary with residual secretion of a bioinactive truncated GH peptide.

Clinical and biochemical consequences of an intragenic growth hormone receptor (GHR) deletion in a large Chinese pedigree.

Growth hormone insensitivity (GHI) may be caused by failure of GH receptor function. Some patients bearing specific GHR mutations differ from classical GHI individuals by extremely elevated GH‐binding protein (GHBP) serum concentrations. We investigated clinical, genetic and biochemical characteristics of a severely growth‐retarded Chinese boy with classical Laron syndrome manifestations.

Alu-Mediated Recombination Defect in IGF1R: Haploinsufficiency in a Patient with Short Stature

Background: The insulin-like growth factor (IGF) receptor (IGF1R) is essential for normal development and growth. IGF1R mutations cause IGF-1 resistance resulting in intrauterine and postnatal growth failure. The phenotypic spectrum related to IGF1R mutations remains to be fully understood. Methods: Auxological and endocrinological data of a patient identified previously were assessed. The patients fibroblasts were studied to characterize the IGF1R deletion, mRNA fate, protein expression and signalling capabilities. Results: The boy, who carries a heterozygous IGF1R exon 6 deletion caused by Alu element-mediated recombination and a heterozygous SHOX variant (p.Met240Ile), was born appropriate for gestational age but developed proportionate short stature postnatally. IGF-1 levels were low-normal. None of the stigmata associated with SHOX deficiency or sporadically observed in IGF1R mutation carriers were present. Nonsense-mediated mRNA decay led to a substantial decline of IGF1R dosage and IGF-1-dependent receptor autophosphorylation but not impaired downstream signalling. Conclusion: We present the first detailed report of an intragenic IGF1R deletion identified in a patient who, apart from short stature, deviates from all established markers that qualify a growth-retarded child for IGF1R analysis. Although such children will usually escape routine clinical mutation screenings, they can contribute to the understanding of factors and mechanisms that cooperate with the IGF1R.