[Clinical and genetic characterization of FIPA (familial isolated pituitary adenomas)]

Pituitary adenomas are common brain tumours at autopsy and radiological series of unselected population. Historically, few epidemiologic data regarding the prevalence of clinically apparent pituitary adenomas have been available. Recently, a cross-sectional study conducted in Liège, Belgium, noted that clinically-apparent pituitary adenomas occurred with a prevalence of 1:1064 inhabitants, which is 3.5-5 times the previously reported prevalence. Pituitary adenomas occur predominantly as sporadic tumors, but also in a familial setting or associated to some familial/isolated tumoral syndromes. The recent characterization of the novel clinical entity FIPA (Familial Isolated Pituitary Adenomas) increased the prevalence of familial pituitary adenomas which account now for about 5% of pituitary tumors. Distinct genetic mechanisms are continuously identified and increase our understanding of the complex clinical presentation and sometimes unpredictable evolution of pituitary adenomas.

Regulation of spermatogenesis in McCune-Albright syndrome: lessons from a 15-year follow-up

CONTEXT

McCune-Albright syndrome (MAS) is a disorder caused by a post-zygotic gain-of-function mutation in the gene encoding the Gs-alpha protein. Sexual precocity, common in girls, has been reported in only 15% of boys, and little is known on the long-term evolution of MAS in males.

OBJECTIVE

In a boy with MAS, we studied spermatogenesis, testis histology, and immunohistochemistry with the aim to shed light on seminiferous tubule activity.

DESIGN

A boy who presented at the age of 2.9 years with sexual precocity, monolateral macroorchidism, increased testosterone levels, and suppressed gonadotropins was followed up until the age of 18.

RESULTS

Throughout follow-up testicular asymmetry persisted and gonadotropin and testosterone pattern did not change. At the age of 18, inhibin B was undetectable while alpha-immunoreactive inhibin was within normal range. Anti-Mullerian hormone level was slightly subnormal. Sperm cells were 3,900,000 per ejaculate. Histology of both testes showed spermatogonia, spermatocytes, and, in some tubes, matured spermatozoa. Sertoli cells were markedly stained with anti-inhibin alpha-subunit antibody in both the testes. There was no immunostaining of Sertoli, Leydig, or germ cells with anti-betaA or anti-betaB antibody. MAS R201H mutation was identified in both the testes.

CONCLUSION

The 15-year follow-up in this boy with MAS demonstrated that autonomous testicular activation and gonadotropin suppression persisted over time. This provides an interesting model of active spermatogenesis despite long-term FSH suppression. It also suggests that FSH is needed for the full expression of the inhibin betaB-subunit gene, an expression previously reported in the germ and Leydig cells of normal adult subjects.

Preimplantation genetic diagnosis for severe albright hereditary osteodystrophy

CONTEXT

Preimplantation genetic diagnosis (PGD) enables the selection of embryos without mutations for implantation and has not been described to our knowledge for mutations in GNAS. Phocomelia in a patient with Albright hereditary osteodystrophy (AHO) has also not been previously described.

OBJECTIVE

The aim of this study was to identify a GNAS mutation in a patient with a severe form of AHO and pseudohypoparathyroidism type 1a with phocomelia and to perform PGD on embryos derived by in vitro fertilization to deliver an unaffected infant.

DESIGN

A proband and his family are described clinically, the GNAS gene was sequenced to identify a novel mutation in the proband, and PGD was performed on embryos.

SETTING

The setting was in a tertiary-care hospital.

PATIENTS

The patients were from a single family in which the proband has a severe form of AHO.

INTERVENTIONS

Interventions were PGD and in vitro fertilization.

MAIN OUTCOME MEASURES

The main outcome measures were the clinical phenotypes and GNAS gene sequences of the proband, embryos, and family members.

RESULTS

After PGD, three genotypically normal embryos were transferred back to the mother. Pregnancy ensued, and a healthy male infant was delivered at 36.5 wk gestation. The GNAS genes in the baby were confirmed as wild-type, and the infant is free of any signs of AHO.

CONCLUSIONS

We describe herein a proband with AHO and severe skeletal deformities (including phocomelia) related to a novel GNAS mutation and the delivery of a male infant with homozygous normal GNAS genotype after PGD.

Clinical and molecular genetics of acromegaly: MEN1, Carney complex, McCune-Albright syndrome, familial acromegaly and genetic defects in sporadic tumors

Pituitary tumors are among the most common neoplasms in man; they account for approximately 15% of all primary intracranial lesions (Jagannathan et al., Neurosurg Focus, 19:E4, 2005). Although almost never malignant and rarely clinically expressed, pituitary tumors may cause significant morbidity in affected patients. First, given the critical location of the gland, large tumors may lead to mass effects, and, second, proliferation of hormone-secreting pituitary cells leads to endocrine syndromes. Acromegaly results from oversecretion of growth hormone (GH) by the proliferating somatotrophs. Despite the significant efforts made over the last decade, still little is known about the genetic causes of common pituitary tumors and even less is applied from this knowledge therapeutically. In this review, we present an update on the genetic syndromes associated with pituitary adenomas and discuss the related genetic defects. We next review findings on sporadic, non-genetic, pituitary tumors with an emphasis on pathways and animal models of pituitary disease. In conclusion, we attempt to present an overall, integrative approach to the human molecular genetics of both familiar and sporadic pituitary tumors.

A maternal epimutation of GNAS leads to Albright osteodystrophy and parathyroid hormone resistance

CONTEXT

Pseudohypoparathyroidism (PHP) type Ia is a rare maternally transmitted disease due to maternal loss-of-function mutations of GNAS, the gene encoding Galphas, the alpha-stimulatory subunit of the G protein. Affected individuals display hormonal resistance (mainly PTH and TSH resistance) and Albright hereditary osteodystrophy. PHP type Ib (PHP-Ib), usually defined by isolated renal resistance to PTH and sometimes mild TSH resistance, is due to a maternal loss of GNAS exon A/B methylation, leading to decreased Galphas expression in specific tissues.

OBJECTIVE AND RESULTS

We report a girl with obvious Albright osteodystrophy features, PTH resistance, normal Galphas bioactivity in red blood cells, yet no loss-of-function mutation in the GNAS coding sequence (exons 1-13). The methylation analysis of the four GNAS differentially methylated regions, i.e. NESP, AS, XL, and A/B, revealed broad methylation changes at all differentially methylated regions, including GNAS exon A/B, leading to a paternal epigenotype on both alleles.

CONCLUSIONS

This observation suggests that: 1) the decreased expression of Galphas due to GNAS epimutations is not restricted to the renal tubule but may affect nonimprinted tissues like bone; 2) PHP-Ib is a heterogeneous disorder that should lead to studying GNAS epigenotype in patients with PHP and no mutation in GNAS exons 1-13, regardless of their physical features.

Cognitive impairment is prevalent in pseudohypoparathyroidism type Ia, but not in pseudopseudohypoparathyroidism: possible cerebral imprinting of Gsalpha

OBJECTIVE

Pseudohypoparathyroidism type Ia (PHP-Ia) is a hereditary disorder characterized by resistance to multiple hormones that work via cAMP such as PTH and TSH, accompanied by typical skeletal features including short stature and brachydactyly, termed Albright hereditary osteodystrophy (AHO). In affected kindreds, some members may have AHO but not hormone resistance; they are termed as pseudopseudohypoparathyroidism (PPHP). The molecular basis for the disorder is heterozygous inactivating mutation of the Gsalpha gene. In affected families, subjects with both PHP-Ia and PPHP have the same Gsalpha mutations. The skeletal features common to PPHP and PHP-Ia are presumably caused by tissue-specific Gsalpha haploinsufficiency. Other features that distinguish between PPHP and PHP-Ia, such as the multihormone resistance, are presumably caused by tissue-specific paternal imprinting of Gsalpha. This suggests that major differences in phenotype between PHP-Ia and PPHP point to specific tissues with Gsalpha imprinting. One such major difference may be cognitive function in PHP-Ia and PPHP.

DESIGN

Description of a large family with PHP-Ia and PPHP.

PATIENTS

Eleven affected subjects with PHP-Ia or PPHP in one family.

MEASUREMENTS

Cognitive impairment (CI) was defined by a history of developmental delay, learning disability and the Wechsler intelligence scale.

RESULTS

CI occurred only in the five PHP-Ia but not in the six PPHP subjects. Hypothyroidism which occurred in all PHP-Ia subjects was apparently not the cause of CI as it was mild, and was treated promptly. Analysis of additional Israeli cases, and the published cases from the literature, all with documented Gsalpha mutations, revealed that CI is prevalent in PHP-Ia [60 of 77 subjects (79%)] but not in PPHP [3 of 30 subjects (10%)] (P < 1 x 10(-6)).

CONCLUSION

We suggest that Gsalpha is imprinted in the brain.

Restoration of ovulation after unilateral ovariectomy in a woman with McCune-Albright syndrome: a case report

INTRODUCTION

McCune-Albright syndrome (MAS) is characterized by peripheral precocious puberty, café-au-lait spots, and polyostotic fibrous dysplasia. This syndrome is due to a post-zygotic mutation of the GNAS1 gene with mosaic distribution and unilateral predominance. Clinical manifestations depend on the tissues carrying the mutation. We describe the ovarian function before and after unilateral ovariectomy in a woman with MAS and bilateral distribution of the GNAS1 gene mutation.

CASE REPORT

A 33-year-old patient, previously diagnosed as having MAS, presented irregular menstrual cycles (30-180 days) and monophasic temperature curves. Transvaginal ultrasound and blood tests were repeated at 3-day intervals over 3 months. Findings included a persistent quiescent left ovary, a persistent polycystic right ovary, constantly high estradiol-17beta (E2) levels, and very low FSH and LH levels. She also presented severe persistent pelvic pain. Because of unilateral ovarian activity, a unilateral right ovariectomy was performed as well as biopsy of the remaining left ovary. A GNAS1 gene mutation was identified in both ovaries. A regular monthly menstrual cycle was immediately restored. On day 3 of the menstrual cycle, E2 level was 30 pg/ml, FSH level was 7.5 mIU/ml, and LH level was 6.4 mIU/ml. On day 17, pelvic ultrasound showed one follicle of 25 mm in the left ovary. On day 21, the progesterone level was 13.1 ng/ml.

DISCUSSION

This is the first report of ovulation being restored following unilateral ovariectomy in an adult patient suffering from severe MAS with GNAS1 gene mutation identified in both ovaries.

Patients with mutations in Gsalpha have reduced activation of a downstream target in epithelial tissues due to haploinsufficiency

CONTEXT

Patients with Albright hereditary osteodystrophy (AHO) have defects in stimulatory G protein signaling due to loss of function mutations in GNAS. The mechanism by which these mutations lead to the AHO phenotype has been difficult to establish due to the inaccessibility of the affected tissues.

OBJECTIVE

The objective of the study was to gain insight into the downstream consequences of abnormal stimulatory G protein signaling in human epithelial tissues.

PATIENTS AND DESIGN

We assessed transcription of GNAS and Gsalpha-stimulated activation of the cystic fibrosis transmembrane conductance regulator (CFTR) in AHO patients, compared with normal controls and patients with cystic fibrosis.

MAIN OUTCOME MEASURES

Relative expression of Gsalpha transcripts from each parental GNAS allele and cAMP measurements from nasal epithelial cells were compared among normal controls and AHO patients. In vivo measurements of CFTR function, pulmonary function, and pancreatic function were assessed in AHO patients.

RESULTS

GNAS was expressed equally from each allele in normals and two of five AHO patients. cAMP generation was significantly reduced in nasal respiratory epithelial cells from AHO patients, compared with normal controls (0.4 vs. 0.6, P = 0.0008). Activation of CFTR in vivo in nasal (P = 0.0065) and sweat gland epithelia (P = 0.01) of AHO patients was significantly reduced from normal. In three patients, the reduction in activity was comparable with patients with cystic fibrosis due to mutations in CFTR. Yet no AHO patients had pulmonary or pancreatic disease consistent with cystic fibrosis.

CONCLUSIONS

In humans, haploinsufficiency of GNAS causes a significant reduction in the activation of the downstream target, CFTR, in vivo.

[Pseudopseudohypoparathyroidism and genomic imprinting]

Pseudopseudohypoparathyroidism (PPHP) is caused by the paternally-derived mutation in the coding region of GNAS gene. The phenotype of PPHP is produced by the sum of both decreased Gsalpha protein in biallelically expressed tissues and other proteins or non-coding RNAs by mutated paternal-allele specific expression. It has been believed that the haploinsufficiency of Gsalpha in non-imprinted tissues is responsible for the Albright hereditary dystrophy (AHO) phenotype. Recently it was reported that obesity is a more prominent feature in pseudohypoparathyroidism type I a than in PPHP. This result implicates paternal imprinting in the development of obesity in pseudohypoparathyroidism type I a. In this review, recent advances in clinical and experimental knowledge in genomic imprinting of GNAS gene were summarized.

[GNAS1 gene abnormality in pseudohypoparathyroidism I a]

Pseudophypoparathyroidism (PHP) is characterized by hypocalcemia, hyperphosphatemia and elevated levels of parathyroid hormone (PTH) due to resistance to PTH. PHP type I a is caused by heterozygous inactivating mutation of the GNAS1 gene, which encodes signal transducer, Gsalpha. PHP type I a is associated with Albright's osteodystrophy (AHO). Those patients who have AHO phenotype without hormone resistance are affected by pseudopseudohypoparathyroidism.

Genetic and molecular aspects of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is characterized by the clinical triad of polyostotic fibrous dysplasia, café-au-lait pigmented skin lesions and endocrinopathy (1,2) The molecular lesion in MAS is a postzygotic mutation in the GNAS gene that leads to activation of Gsalpha, the alpha chain of the heterotrimeric G protein, Gsalpha. Cells that carry the activating mutation are distributed in a mosaic pattern. A clinical diagnosis of MAS can be made when a patient is found to have at least two features of the classical triad (3). Because of the restricted pattern of distribution of the GNAS mutation, termed gsp, initial molecular analyses were limited to lesional tissue, but recent techniques such as peptide nucleic acid clamping have improved the sensitivity of current assays and now enable the detection of gsp mutations in circulating cells from many patients with MAS.

GNAS mutation detection is related to disease severity in girls with McCune-Albright syndrome and precocious puberty

BACKGROUND

McCune-Albright syndrome (MAS) is characterized by a triad of gonadotropin-independent precocious puberty, café au lait skin pigmentation and fibrous dysplasia of bone. MAS is due to activating mutations of GNAS, the gene encoding Gsalpha. Interest exists in the use of GNAS mutation analysis to make a definitive diagnosis when the phenotype is not diagnostic, i.e. in partial forms of MAS. The utility of using peripheral blood for mutation analysis in this setting has not been thoroughly evaluated.

OBJECTIVE

We performed a systematic analysis of genomic DNA for the detection of GNAS activating mutations in girls with MAS who presented with precocious puberty to evaluate whether identification of an activating mutation in peripheral blood is related to the presence of other features of MAS.

STUDY DESIGN

Genomic DNA was isolated from blood from 13 girls with gonadotropin-independent precocious puberty. A polymerase chain reaction (PCR)-based technique was performed for GNAS mutation identification.

RESULTS

GNAS activating mutations were identified in 4 patients, all of whom had classic MAS based on clinical evidence.

CONCLUSIONS

Detection of activating mutations in leukocyte genomic DNA extracted from peripheral blood samples from girls with gonadotropin-independent precocious puberty was associated with the presence of other phenotypic manifestations of MAS. Until improvements in the diagnostic utility of GNAS activating mutation analysis from leukocyte genomic DNA occur, such testing in patients with atypical forms of MAS should continue to be reserved for research settings.

Epigenetic defects of GNAS in patients with pseudohypoparathyroidism and mild features of Albright's hereditary osteodystrophy

CONTEXT

Several endocrine disorders that share resistance to PTH are grouped under the term pseudohypoparathyroidism (PHP). PHP type I, associated with blunted PTH-induced nephrogenous cAMP formation and phosphate excretion, is subdivided according to the presence or absence of additional endocrine abnormalities, Albright's hereditary osteodystrophy (AHO), and reduced Gsalpha activity caused by GNAS mutations.

OBJECTIVE

We sought to identify the molecular defect in four unrelated patients who were thought to have PHP-Ia because of PTH and TSH resistance and mild AHO features.

METHODS

Gsalpha activity and mutation analysis, and assessment of GNAS haplotype, methylation, and gene expression were performed for probands and family members.

RESULTS

Two patients showed modest decreases in erythrocyte Gsalpha activity. Instead of Gsalpha point mutations, however, all four patients showed methylation defects of the GNAS locus, a feature previously described only for PHP-Ib. Furthermore, one patient with an isolated loss of GNAS exon A/B methylation had the 3-kb STX16 deletion frequently identified in PHP-Ib patients. In all but one of the remaining patients, haplotype analysis excluded large deletions or uniparental disomy as the cause of the observed methylation changes.

CONCLUSIONS

Our investigations indicate that an overlap may exist between molecular and clinical features of PHP-Ia and PHP-Ib. No current mechanisms can explain the AHO-like features of our patients, some of which may not be linked to GNAS. Therefore, patients with hormone resistance and AHO-like features in whom coding Gsalpha mutations have been excluded should be evaluated for epigenetic alterations within GNAS.

A disruptive mutation in exon 3 of the GNAS gene with albright hereditary osteodystrophy, normocalcemic pseudohypoparathyroidism, and selective long transcript variant Gsalpha-L deficiency

OBJECTIVE

The GNAS gene encodes the alpha-subunit of stimulatory G proteins, which play a crucial role in intracellular signal transduction of peptide and neurotransmitter receptors. In addition to transcript variants that differ in their first exon due to different promoters, there are two long (Gsalpha-L) and two short (Gsalpha-S) splice variants, created by alternative splicing. Heterozygous inactivating maternally inherited mutations of GNAS lead to a phenotype in which Albright hereditary osteodystrophy is associated with pseudohypoparathyroidism type Ia.

METHODS AND RESULTS

The GNAS gene of a 10-yr-old girl with brachymetacarpia, mental retardation, normocalcemic pseudohypoparathyroidism, and hypothyroidism was investigated. We found a heterozygous insertion of an adenosine in exon 3 altering codon 85 and leading to a frame shift inducing a stop codon in exon 4. Molecular studies of cDNA from blood RNA demonstrated normal, biallelic expression of Gsalpha-S transcripts, whereas expression of Gsalpha-L transcripts from the maternal allele was reduced. Immunoblot analysis revealed a reduced Gsalpha-L protein level to about 50%, whereas the protein level of Gsalpha-S was unaltered. Furthermore, the Gsalpha protein activity in erythrocyte membranes was diminished to about 75% of normal. Both the reduced activity and the mutation were also found in the mother and the affected younger brother.

CONCLUSION

This report demonstrates the first evidence for a pathogenic mutation in exon 3 of the GNAS gene. The mutation is associated with a phenotype of Albright hereditary osteodystrophy and pseudohypoparathyroidism type Ia due to selective deficiency of Gsalpha-L and a partial reduction of Gsalpha activity.

A novel MEN1 intronic mutation associated with multiple endocrine neoplasia type 1

OBJECTIVE

To investigate a family with an unusual combination of multiple endocrine neoplasia (MEN1) and the McCune-Albright syndrome for MEN1 mutations and activating GNAS1 mutations at codons Arg201 and Gln227.

METHODS

DNA sequences analyses were performed of the MEN1 gene and codons Arg201 and Gln227 of the GNAS1 gene, using leucocyte and endocrine tissue DNA.

RESULTS

A c-->g transversion at position -9 bp in intron 9 of the MEN1 gene was identified. This resulted in the generation of a BmrI restriction endonuclease site, and its presence and segregation with MEN1 in the family was demonstrated by restriction endonuclease analysis. The c-->g transversion was shown to result in the generation of a novel acceptor splice site (ccag) using reverse transcriptase-polymerase chain reaction (RT-PCR) and ribonucleic acid (RNA) obtained from Epstein-Barr virus (EBV)-transformed lymphoblasts. Utilization of this splice site resulted in an abnormal messenger RNA (mRNA) transcript that contained an additional eight bases. This predicted a frameshift that would result in nine missense amino acids followed by a premature termination signal. GNAS1 mutations were not detected in the patient with McCune-Albright syndrome.

CONCLUSIONS

The occurrence of MEN1 and the McCune-Albright syndrome in this family are coincidental findings and not due to a common genetic aetiology. However, our results have identified a novel MEN1 mutation that occurs in intron 9 and generates a novel acceptor splice site. Such splicing-affecting genomic variants (SpaGVs) are increasingly being recognized as a cause of human disease, and are likely to be of significance in the 10% of MEN1 patients who do not have coding region mutations.

Genetic diagnosis of multiple affected tissues in a patient with McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a sporadic disorder characterized by the classic triad of polyostotic fibrous dysplasia, café-au-lait' skin pigmentation, and hyperfunctional endocrinopathy. It is caused by embryonic somatic mutations leading to the substitution of His or Cys for Arg at amino acid 201 of the alpha-subunit of the signal transduction protein Gs (Gsalpha). A 32-year-old man was diagnosed as McCune-Albright syndrome with the following findings: polyostotic fibrous dysplasia, café-au-lait' spots and acromegaly. An ultrasonic examination showed that he had left-pleural effusion, which disappeared after almost a year without special treatment. Genomic DNA was isolated from the peripheral blood, bone tissue, skin lesion and pleura samples of the patient. Then PCR and direct sequencing were performed. An activating mutation of the Gsalpha gene (Arg201Cys) was found in the genomic DNA isolated from the peripheral blood and the bone tissue, but not in genomic DNA isolated from the skin and pleura samples.

A case of McCune-Albright syndrome with associated multiple endocrinopathies

McCune-Albright syndrome (MAS) is a rare disorder that develops from an activating mutation in the Gs gene. It is characterized by an association with Polyostotic fibrous dysplasia, and precocious puberty, Caf-au-lait pigmentation, and other endocrinopathies that result from the hyperactivity of a variety of endocrine glands. Recently we encountered a patient with MAS with fibrous dysplasia, skin pigmentation, acromegaly, hyperprolactinemia and a thyroid nodule. A 23-year-old male presented for an evaluation of a change in his facial structures. Fibrous dysplasia was diagnosed by a bone biopsy and radiographic studies. The GH level increased paradoxically after an oral glucose load. The plasma prolactin, IGF-1 and alkaline phosphatase were high. Thyroid ultrasonography revealed multiple nodules. The brain MRI demonstrated a mass in the left pituitary gland. Genetic analysis identified a change from Arg (CGT) at codon 201 to Cys (TGT).

McCune-Albright syndrome with acromegaly and fibrous dysplasia associated with the GNAS gene mutation identified by sensitive PNA-clamping method

A 16-year-old girl presented with McCune-Albright syndrome associated with acromegaly and fibrous dysplasia. Brain MRI demonstrated a pituitary tumor. X-ray films showed bone deformities, and 99TmO4 bone scintigraphy revealed increased uptake of radioactivity in the affected bones. Although the serum FGF23 level was increased, the serum calcium, phosphate, and active vitamin D levels were all within normal limits. GNAS gene mutation was detected at neither codon 201 nor 227 by conventional PCR-based direct sequencing analysis. We performed a selective PCR with peptide nucleic acid (PNA) clamping to increase the sensitivity for gene mutation detection and identified the R201C GNAS mutation.

G(s)alpha mutations in fibrous dysplasia and McCune-Albright syndrome

Fibrous dysplasia (FD) is a focal bone lesion composed of immature mesenchymal osteoblastic precursor cells. Some FD patients also have hyperpigmented skin lesions (café-au-lait spots), gonadotropin-independent sexual precocity, and/or other endocrine and nonendocrine manifestations (McCune-Albright syndrome [MAS]). MAS results from somatic mutations occurring during early development, resulting in a widespread mosaic of normal and mutant-bearing cells, which predicts that the clinical presentation of each patient is determined by the extent and distribution of abnormal cells. These mutations encode constitutively active forms of G(s)alpha, the ubiquitously expressed G protein alpha-subunit that couples hormone receptors to intracellular cAMP generation. These mutations lead to substitution of amino acid residues that are critical for the intrinsic GTPase activity that is normally required to deactivate the G protein. This leads to prolonged activation of G(s)alpha and its downstream effectors even with minimal receptor activation. This explains why MAS patients have stimulation of multiple peripheral endocrine glands in the absence of circulating stimulatory pituitary hormones and increased skin pigment, which is normally induced by melanocyte-stimulating hormone through G(s)alpha/cAMP. Similar mutations are also present in 40% of pituitary tumors in acromegaly patients and less commonly in other endocrine tumors. FD results from increased cAMP in bone marrow stromal cells, leading to increased proliferation and abnormal differentiation. Parental origin of the mutated allele may also affect the clinical presentation, because G(s)alpha is imprinted and expressed only from the maternal allele in some tissues (e.g., pituitary somatotrophs).

Mutations in the Gs alpha gene causing hormone resistance

G-protein-coupled receptors (GPCRs) and G proteins mediate the effects of a number of hormones of relevance to endocrinology. Genes encoding these molecules may be targets of loss- or gain-of-function mutations, resulting in endocrine disorders. The only mutational change of G proteins so far unequivocally associated with endocrine disorders occurs in the Gsalpha gene (GNAS1, guanine nucleotide binding protein alpha stimulating activity polypeptide 1), which activates cyclic AMP (cAMP)-dependent pathways. Heterozygous loss-of-function mutations of GNAS1 in the active maternal allele cause resistance to hormones acting through Gsalpha-coupled GPCRs, whereas somatic gain-of-function mutations cause proliferation of endocrine cells recognizing cAMP as mitogen. This review will focus on inactivating mutations leading to hormone resistance syndromes, i.e., pseudohypoparathyroidism types Ia and Ib.

Searching for somatic mutations in McCune-Albright syndrome: a comparative study of the peptidic nucleic acid versus the nested PCR method based on 148 DNA samples

BACKGROUND

Activating mutations of the Gsalpha gene (GNAS), which encodes for the alpha-subunit of the stimulatory G protein, have been identified in patients with McCune-Albright syndrome (MAS). Accuracy and sensitivity in the molecular diagnosis of MAS is mandatory for optimal therapeutic strategy and adapted follow-up, especially for incomplete clinical forms of MAS. To date, the highly sensitive nested PCR method with intermediary digestion by a restriction enzyme at the mutation site is one of the most widely used techniques. This study evaluated a new diagnostic method using a peptidic nucleic acid (PNA) and compared it with the nested PCR method.

MATERIAL AND METHODS

One hundred and forty-eight DNA samples from eighty-eight patients presenting clinical symptoms compatible with MAS were included. The DNA samples were mainly obtained from peripheral blood, ovarian tissue or cyst liquid, and bone lesions. The nested PCR method required 4 days. PNA clamping required 1.5 days and utilized the higher thermal stability and specificity of PNA-DNA coupling to inhibit PCR product formation. Direct sequencing was subsequently performed in all cases.

RESULTS

The sensitivity of mutation detection was 54% (n = 80) for nested PCR and 46.6% (n = 69) for PNA (P > 0.05). The 11 cases where PNA failed to detect the mutation were mainly incomplete and atypical clinical forms of MAS (n = 10/11). The cost per sample was 50 Euros for PNA clamping versus 136 Euros for nested PCR.

CONCLUSION

PNA clamping is a rapid, reliable, and economical method to diagnose MAS. It should be the first-line diagnostic method, although negative results, especially for incomplete clinical forms of MAS, should be confirmed by nested PCR.

Unexpected mosaicism of R201H-GNAS1 mutant-bearing cells in the testes underlie macro-orchidism without sexual precocity in McCune-Albright syndrome

McCune-Albright syndrome (MAS), usually presenting with polyostotic bone dysplasia, café-au-lait skin lesions and sexual precocity, results from a somatic activating mutation of the GNAS1 gene, which encodes the Gs-alpha protein involved in signalling of several G-protein-coupled receptors. The clinical spectrum depends on tissue distribution of mutant-bearing cells. Sexual precocity has been ascribed to the occurrence of a mutant GNAS1 allele in the gonadal anlage, from which all somatic cells of the differentiated gonads arise. In boys, precocious activation of Leydig cell androgen secretion results in pubertal spermatogenesis, leading to testicular enlargement, and in the development of secondary sex characteristics. However, sexual precocity is rare in MAS males while isolated testicular enlargement is frequently observed. We recently reported the case of a boy with macro-orchidism and signs of Sertoli cell hyperactivity but no signs of hyperandrogenism, which was unexpected since Gs-alpha is functional in both Sertoli and Leydig cells. To understand its pathophysiology, we microdissected an available testicular biopsy to separate Sertoli from Leydig cells. The R201H-GNAS1 allele was present only in Sertoli cells, resulting in isolated Sertoli cell hyperfunction, evidenced by increased AMH expression and cell hyperplasia leading to prepubertal macro-orchidism, with no signs of Leydig cell activation. The different early embryologic origin of precursors contributing to Sertoli and Leydig cell lineages may underlie the differential existence of the mutated GNAS1 gene. Lack of occurrence of the mutation in Leydig cells may explain why sexual precocity is rarely observed in boys with MAS.

Calcinosis cutis bei hereditärer Albright-Osteodystrophie

Albright hereditary osteodystrophy (AHO) is characterized by a symptom complex including short stature, brachymetacarpia, obesity, round facies, cutaneous osteomas, and mental retardation. AHO is caused by mutations in the GNAS-gene localized on chromosome 20 encoding for Gsalpha protein, a signal transducer of endocrine pathways. Therefore, AHO is often associated with endocrinopathy such as pseudohypoparathyroidism or hypothyroidism. A nine-month-old boy presented with typical features of this syndrome. The diagnosis was confirmed by biochemical and molecular analyses. An unusual feature was calcinosis cutis at such an early age, which led to extensive differential diagnostic procedures.

Pegvisomant for the treatment of gsp-mediated growth hormone excess in patients with McCune-Albright syndrome

CONTEXT

GH excess affects approximately 20% of the patients with McCune-Albright syndrome (MAS). MAS is caused by sporadic, postzygotic, activating mutations in the GNAS gene, which codes for the cAMP-regulating protein, G(s)alpha (gsp oncogene). These same mutations are found in approximately one third of the sporadic cases of acromegaly.

OBJECTIVE

We examined efficacy of the GH receptor antagonist, pegvisomant, in controlling gsp oncogene-mediated GH excess and skeletal disease (fibrous dysplasia of bone) associated with MAS.

SETTING AND PATIENTS

Five MAS patients with GH excess were treated with 20 mg/d sc injection of pegvisomant for 12 wk in a randomized, double-blind, placebo-controlled crossover study at the National Institutes of Health.

MAIN OUTCOME MEASURES

The primary measure of efficacy was normalization of IGF-I. Secondary outcome measures were reduction in serum IGF binding protein-3 (IGFBP-3), improvement of fatigue and sweating, and reduction in markers of bone metabolism and bone pain.

RESULTS

Combined mean changes in serum IGF-I at 6 and 12 wk were -236.4 ng/ml (53%, P < 0.005) and -329.8 ng/ml (62%, P < 0.001), respectively. IGFBP-3 decreased by 0.8 mg/liter (24%, P < 0.01) and 2.9 mg/liter (37%, P < 0.005), respectively. There were no significant changes in signs and symptoms of acromegaly or markers of bone metabolism and bone pain, nor was there a significant change in pituitary size. Retrospective comparison of the degree of control achieved with pegvisomant vs. other medications (long-acting octreotide +/- dopamine agonist) in the same group showed that the two regimens were similarly effective.

CONCLUSIONS

Pegvisomant effectively reduced IGF-I and IGFBP-3 levels in gsp-mediated GH excess but had no effect on fibrous dysplasia.

Identification of a second-site suppressor mutation of the GTPase defect associated with McCune-Albright syndrome: a model using the yeast heterotrimeric G protein, GPA1

McCune-Albright syndrome (MAS) causes a variety of bone and endocrine abnormalities due to the post-zygotic mutation of the alpha subunit of the stimulatory G-protein Gsalpha. This mutation causes signal-independent activity of the G-protein in the affected cells. We report the development of a system to study the effects of MAS mutations using Saccharomyces cerevisiae, wherein activation of the yeast G-protein pathway results in growth arrest in a genetically recessive fashion. We introduced the MAS mutation into the analogous site in the yeast Galpha gene, GPA1 and randomly mutated the gene to produce intragenic suppressors. Yeast with normal and mutated G-protein genes were induced to lose the normal gene, and mutations able to intragenically suppress the constitutive activity of the MAS mutation were identified based on their ability to form colonies. We report one mutation in GPA1, also in the active site, that is an intragenic suppressor of the MAS defect.

Determination of Gs alpha protein activity in Albright's hereditary osteodystrophy

Albright's hereditary osteodystrophy (AHO) is a heterogeneous clinical entity in part associated with pseudohypoparathyroidism (PHP) and other endocrinopathies. It may be caused by diminished Gs alpha protein activity. Heterozygous mutations in the underlying GNAS gene on chromosome 20 have been described. One hundred and six patients with suspected AHO, were investigated, of whom 93 showed a laboratory profile of PHP with low or normal calcium and elevated parathormone with normal vitamin D metabolites, and 13 had no endocrine abnormalities. Gs alpha activity was determined in isolated erythrocyte membranes. Molecular genetic analysis of GNAS exons 2-13 was initiated. Significantly reduced Gs alpha activity was found in 91 patients. In 53 patients with reduced Gs alpha activity, a mutation within GNAS was demonstrated. The mutation detection rate was much lower in AHO patients without endocrinopathies than in those who had PHP. In addition, three of the 15 patients with AHO features but normal Gs alpha activity had genetic variations of GNAS. We conclude that determination of Gs alpha activity can be used as a diagnostic screening procedure in patients with suspected AHO. However, the mutation detection rate in GNAS is highly variable. The genetic heterogeneity of AHO needs further investigation.

Laparoscopic management of ovarian cysts in peripheral precocious puberty of McCune-Albright syndrome

Ovarian cysts are common in peripheral precocious puberty in McCune-Albright syndrome (MAS). The clinical course of these cysts is unpredictable due to episodes of hyperestrogenism typical of MAS ovarian hyperfunction. In persistent and recurrent large ovarian cysts with sustained estrogen hypersecretion and relevant clinical disturbances (increased linear growth and bone age maturation, vaginal bleeding and psychological disturbances) treatment is mandatory. Experimental courses of estrogen-blocking drugs may have insufficient or nil therapeutic effects. In these cases and when molecular analysis is required to obtain MAS diagnosis as in isolated peripheral precocious puberty, surgery is the option. Laparoscopy minimizes surgical aggression and facilitates obtaining tissue samples for molecular analysis, and sometimes relieves hyperestrogenism with the excision of hyperactive ovarian areas. It can be conducted with trans-umbilical laparoscopic ovarian cystectomy (TULOC) before 3 years of age and with traditional techniques afterwards.

McCune-Albright syndrome: clinical picture and natural history in children and adolescents

The classical triad of McCune-Albright syndrome (MAS) consists of polyostotic fibrous dysplasia (FD), skin hyperpigmentation (café-au-lait spots), and endocrine dysfunction, frequently seen in females as precocious puberty. Patients with MAS display mosaicism of activating somatic mutations of the alpha-subunit of Gs. Thus, the clinical presentation of each individual is dependent on the particular distribution of affected cells, causing a broad spectrum of endocrine and non-endocrine manifestations. Typical endocrinopathies are precocious puberty, hyperthyroidism, growth hormone excess, hyperprolactemia, and hypercortisolism. The onset of these manifestations is usually during infancy and childhood. Since specific treatment is required, the prognosis depends on the severity of each individual endocrine manifestation. Additionally, there are non-endocrine manifestations, such as fibrous dysplasia of bone (FD), renal phosphate wasting, and skin hyperpigmentation, i.e. café-au-lait spots. FD, mostly polyostotic, causes fractures needing surgical and orthopedic treatment. Since previous studies have suggested the overall prognosis of patients with McCune-Albright syndrome to be non-fatal, recent data have drawn our attention to non-endocrine affections, including hepatobiliary dysfunction and cardiac disease, which are probably an important risk factor for early death. In summary, the clinical picture in MAS is related to its mosaic nature, i.e. any cell, tissue and organ in any site of the body could be affected to varying degrees, ranging from one or two mild clinical signs with excellent long-term prognosis to a severe life-threatening multiorgan disease.

Genetics of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a rare proteiform disease due to postzygotic, somatic mutations at codon R201 of the GNAS1 gene that results in cellular mosaicism. Different methods have been used in the molecular analysis of DNA samples from several tissues of patients with one or more MAS signs, with various mutation detection rates. We review data from the literature to investigate whether patient inclusion criteria for GNAS1 analysis, the molecular methods used to search for R201 mutations, and the type of tissues analysed, can influence the mutation detection rate in MAS. Our study indicates that to overcome the problems related to GNAS1 analysis in MAS, sensitive and specific molecular methods must be used to look for the mutation from all available affected tissues and from easily accessible tissues, and even more so in the presence of atypical and monosymptomatic forms of MAS.

Genetics of pseudohypoparathyroidism types Ia and Ic

Pseudohypoparathyroidism (PHP) types Ia and Ic result from heterozygous inactivating mutations of Gs alpha, the alpha-subunit of the heterotrimeric stimulatory G-protein, Gs. Both are characterized by a combination of Albright's hereditary osteodystrophy and, when the mutation is maternally inherited, end-organ resistance to multiple hormones. Due to complex tissue-specific imprinting of Gs alpha, paternally-derived mutations do not usually lead to hormone resistance. More than 100 mutations have been characterized in patients with PHP-Ia and one mutation in type Ic. These are scattered throughout the gene, with one significant mutational hotspot in exon 7. Identification of mutations in a clinical service setting is important for accurate genetic counselling and clinical management of affected families. However, only 70-80% of mutations are identified by direct sequencing of coding exons and splice junctions. Screening for whole exon deletions and intronic or regulatory mutations in mutation-negative families is therefore now an important priority to establish the full mutational spectrum in these conditions.

Expression of FGF23 is correlated with serum phosphate level in isolated fibrous dysplasia

Fibrous dysplasia (FD) patients sometimes suffer from concomitant hypophosphatemic rickets/osteomalacia, resulting from renal phosphate wasting. It was recently reported that FD tissue in the patients with McCune-Albright syndrome (MAS) expressed fibroblast growth factor-23 (FGF-23), which is now known to be as a pathogenic phosphaturic factor in patients with oncogenic osteomalacia and X-linked hypophosphatemic rickets. Since it remains controversial whether serum phosphate levels are influenced by FGF23 expressions in FD tissue, isolated FD patients without MAS syndrome were examined for the relationship between FGF23 expressions, circulating levels of FGF-23 and phosphate to negate the effects of MAS-associated endocrine abnormalities on serum phosphate. Eighteen paraffin embedded FD tissues and 2 frozen tissues were obtained for the study. Sixteen of 18 isolated FD tissues were successfully analyzed GNAS gene, which exhibited activated mutations observed in MAS. Eight of 16 FD tissues, which exhibited GNAS mutations, revealed positive staining for FGF-23. These evidence indicate that postzygotic activated mutations of GNAS is necessary for the FD tissue formation by mosaic distribution of mutated osteogenic cell lineage, but is not sufficient to elevate FGF23 expression causing generalized osteomalacia with severe renal phosphate wasting. The expression level of FGF23 in isolated FD tissue with hypophosphatemic osteomalacia determined by real-time PCR was abundant close to the levels in OOM tumors. Osteoblasts/osteocytes in woven bone were predominant source of circulating FGF-23 in FD tissues by immunohistochemistry. A negative correlation of the intensity of FGF-23 staining with serum inorganic phosphate levels indicated that the expression of FGF23 in focal FD tissues could be a prominent determinant of serum phosphate levels in isolated FD patient. These data provide novel insights into the regulatory mechanism of serum inorganic phosphate levels in isolated FD patients and extend the notion that FGF-23 originating from FD tissue may cause hypophosphatemia not only in isolated FD patients but also in the patients with MAS syndrome.

[Clinical features and pathogenesis of Carney complex, a rare form of multiple endocrine neoplasia syndromes]

Carney-complex is the rarest and most recently described form of multiple endocrine neoplasia syndromes that is unique both from clinical and pathogenetic aspects. Clinical features include spotty skin pigmentation, cutaneous and cardiac myxomas, multiple endocrine abnormalities and schwannomas. The most characteristic endocrine abnormality is primary pigmented nodular adrenal hyperplasia that may result in clinically apparent Cushing's syndrome. Acromegaly, hyperprolactinaemia, tumours of the testis and ovaries have also been described. Approximately fifty percent of Carney-complex cases are familial, with an autosomal dominant inheritance pattern. About 45-65% of Carney-complex cases are related to mutations of the PRKAR1A gene encoding a regulatory subunit of protein kinase A, but other genetic mechanisms seem to be involved, as well. Here, the authors present a brief synopsis of its clinical and pathogenetical features.

McCune-Albright syndrome in a boy may present with a monolateral macroorchidism as an early and isolated clinical manifestation

BACKGROUND

Testis enlargement in McCune-Albright syndrome (MAS) is generally bilateral and associated with clinical and biochemical manifestations of sexual precocity.

CASE REPORT

We describe for the first time an unreported clinical expression of MAS in a 4.6-year-old boy presenting with monolateral testis enlargement and no signs of sexual precocity or other clinical manifestations of MAS at the time of presenting with macroorchidism. Both testosterone and LHRH-stimulated gonadotropin levels were in the prepubertal range. Serum inhibin B was increased to a pubertal level indicating Sertoli cell activation. The histological and immunocytochemical evaluation of the enlarged testis revealed Sertoli cell hyperplasia with no mature Leydig cells. Mutation R201C of GNAS1 gene, classically responsible for MAS, was identified in DNA samples from the right testis biopsy and leukocytes.

CONCLUSIONS

(a) MAS should be taken into consideration in the clinicopathological approach to a boy with monolateral macroorchidism; (b) testicular enlargement may be only the presenting clinical manifestation of MAS and is not necessarily linked to manifestations of peripheral precocious puberty; (c) testicular autonomous hyperfunction in MAS may be restricted to Sertoli cells, as also demonstrated previously by others.

A case of McCune-Albright syndrome associated with Gs alpha mutation in the bone tissue

The syndrome of McCune-Albright syndrome (MAS) is clasically defined as a triad presentation with the findings of polyostotic fibrous dysplasia, café-au-lait spots, and sexual precocity. However, not all patients present with complete symptoms. A 52-year-old man was diagnosed as having a variant of McCune-Albright syndrome with the following findings: polyostotic fibrous dysplasia, acromegaly due to pituitary tumor and subclinical hyperthyroidism due to toxic multinodular goiter. Sexual precocity and café-au-lait spots were not noted. Acromegaly was confirmed by laboratory examination (IGF-1, glucose suppression test and TRH stimulation test). Long acting somatostatin analogue was used as treatment. Although the pituitary tumor could not be removed due to technical problems, mass lesions on the cranium were removed subtotally. Histopathological evaluation demonstrated that the lesion complied with fibrous dysplasia. Genomic DNAs were isolated from the craniofacial bones and peripheral leucocytes of the patient. After amplifying the related regions, Gs alpha (Gs alpha) gene was analysed by automatic DNA sequence analysis. An activating mutation of the Gs alpha gene (Arg 201 Cys) was found in the genomic DNA isolated from the bone tissue of the patient, but not in the genomic DNA isolated from the blood. We described a case of MAS associated with Gs alpha mutation in the bone tissue, presenting with polyostotic fibrous dysplasia, subclinical hyperthyroidism and acromegaly.

Clinical approach to clarifying the mechanism of abnormal bone metabolism in McCune-Albright syndrome

Recent advances in our knowledge of the abnormal bone metabolism associated with McCune-Albright syndrome (MAS) is briefly reviewed. Polyostotic fibrous bone dysplasia and hypophosphatemia are well-known characteristics of MAS. To clarify the mechanism of bone dysplasia, an approach that uses human cells isolated from MAS patients was important. It is now clear that normal skeletal stromal cells without mutation of the Gsalpha protein are necessary for the presence of bone dysplasia and that exaggerated production of interleukin-6 by fibrous bone cells with mutation of the Gsalpha protein is linked to the increased number of osteoclasts in bone tissues. The observation of increased bone resorption by the increased osteoclasts is one of the reasons for using bisphosphonates to treat the bone lesions of MAS. The key observation of the mechanism of hypophosphatemia in MAS was in a clinical report, which suggested that the presence of some humoral factors regulate phosphate metabolism. Recently, the humoral factor that causes hypophosphatemia in MAS was clarified to be fibroblast-growth factor 23 (FGF-23), although the possibility of some other humoral factors was not excluded. This is because a humoral factor inhibiting intestinal phosphate transport is present in culture medium obtained from the cells derived from fibrous bone dysplasia. The abnormal vitamin D mechanism in response to hypophosphatemia in MAS patients also proved recently to be caused by the increased circulating FGF-23 levels. The lines of evidence described suggest that FGF-23 and other factors may coexist, causing hyperphosphaturia and impaired intestinal absorption of phosphate, respectively.

Molecular delineation of deletions on 2q37.3 in three cases with an Albright hereditary osteodystrophy-like phenotype

A minority of the reported cases of terminal 2q37 deletion clinically resemble Albright hereditary osteodystrophy (AHO)/pseudopseudohypoparathyroidism and have only mild-to-moderate mental retardation. Our molecular and cytogenetic fluorescence in situ hybridization (FISH) findings on an additional three patients further reduce the size of the minimal critical region deleted in this syndrome to about 3 Mb. This region includes the G-protein-coupled receptor 35 (GPR35), glypican 1 (GPC1), and serine/threonine protein kinase 25 (STK25) genes on 2q37.3. We have further defined several polymorphic variants within the coding region and flanking regions of GPR35 gene, which could potentially be useful for rapid detection of GPR35 gene deletion. We postulate that the absence of GPR35 may, at least partly, account for the phenotypic resemblance to the AHO. We also believe that the deletion of GPR35 could be responsible for the entity brachydactyly mental retardation syndrome (OMIM #600430), which was coined based on the above minority of patients with terminal 2q37 deletion. We recommend that every patient with AHO phenotype should undergo 2q subtelomeric FISH screen and subsequently a molecular study on the GPR35 gene. GPC1 and/or STK25 haploinsufficiency may also contribute to the AHO-like phenotype.

A mouse model of albright hereditary osteodystrophy generated by targeted disruption of exon 1 of the Gnas gene

Albright hereditary osteodystrophy is caused by heterozygous inactivating mutations in GNAS, a gene that encodes not only the alpha-chain of Gs (Galphas), but also NESP55 and XLalphas through use of alternative first exons. Patients with GNAS mutations on maternally inherited alleles are resistant to multiple hormones such as PTH, TSH, LH/FSH, GHRH, and glucagon, whose receptors are coupled to Gs. This variant of Albright hereditary osteodystrophy is termed pseudohypoparathyroidism type 1a and is due to presumed tissue-specific paternal imprinting of Galphas. Previous studies have shown that mice heterozygous for a targeted disruption of exon 2 of Gnas, the murine homolog of GNAS, showed unique phenotypes dependent on the parent of origin of the mutated allele. However, hormone resistance occurred only when the disrupted gene was maternally inherited. Because disruption of exon 2 is predicted to inactivate Galphas as well as NESP55 and XLalphas, we created transgenic mice with disruption of exon 1 to investigate the effects of isolated loss of Galphas. Heterozygous mice that inherited the disruption maternally (-m/+) exhibited PTH and TSH resistance, whereas those with paternal inheritance (+/-p) had normal hormone responsiveness. Heterozygous mice were shorter and, when the disrupted allele was inherited maternally, weighed more than wild-type littermates. Galphas protein and mRNA expression was consistent with paternal imprinting in the renal cortex and thyroid, but there was no imprinting in renal medulla, heart, or adipose. These findings confirm the tissue-specific paternal imprinting of GNAS and demonstrate that Galphas deficiency alone is sufficient to account for the hormone resistance of pseudohypoparathyroidism type 1a.

A highly sensitive polymerase chain reaction method detects activating mutations of the GNAS gene in peripheral blood cells in McCune-Albright syndrome or isolated fibrous dysplasia

BACKGROUND

The somatic nature of mutations in the GNAS gene in McCune-Albright syndrome and isolated fibrous dysplasia makes their identification difficult. Conventional methods for the detection of mosaic mutations of GNAS have required polymerase chain reaction analysis of genomic DNA from affected tissues or multiple rounds of tandem polymerase chain reaction and endonuclease digestion to enrich for mutant alleles in genomic deoxyribonucleic acid (DNA) from other tissues. Peptide nucleic acid (PNA) primers specifically block synthesis from the nonmutant or wild-type allele. We therefore used PNA-clamping to detect low copy numbers of mutant GNAS alleles in DNA from peripheral blood cells from patients with McCune-Albright syndrome and fibrous dysplasia.

METHODS

We applied the PNA-clamping method to the analysis of genomic DNA from peripheral blood cells of thirteen patients with McCune-Albright syndrome and three patients with isolated fibrous dysplasia. Polymerase chain reaction was performed in the presence and absence of PNA, and the polymerase chain reaction products were sequenced. In the absence of PNA, a strong 325 base-pair polymerase chain reaction band was generated from all samples; in the presence of PNA, there was an approximately 50% to 90% reduction in the intensity of this polymerase chain reaction product.

RESULTS

In the absence of PNA, direct sequencing of the polymerase chain reaction products demonstrated R201 mutations in GNAS alleles of three of the thirteen patients with McCune-Albright syndrome and none of the three patients with fibrous dysplasia. In contrast, in the presence of PNA, R201 mutations were detected in eleven of the thirteen patients with McCune-Albright syndrome and in all three of the patients with fibrous dysplasia. In mixing experiments involving the use of wild-type and mutant DNA samples, we were able to determine the presence of a mutant GNAS allele in the equivalent of one cell in 1000 to 5000 cells.

CONCLUSIONS

Inclusion of a specific PNA primer in the polymerase chain reaction for GNAS exon 8 allows the selective amplification of low numbers of mutant alleles, and it permits detection of activating mutations in genomic DNA from peripheral blood cells in patients with McCune-Albright syndrome and fibrous dysplasia.

Genetic and hereditary aspects of childhood obesity

Genetic factors are involved in the regulation of body weight and in determining individual responses to environmental factors such as diet and exercise. The identification and characterization of monogenic obesity syndromes have led to an improved understanding of the precise nature of the inherited component of severe obesity and has had undoubted medical benefits, whilst helping to dispel the notion that obesity represents an individual defect in behaviour with no biological basis. For individuals at highest risk of the complications of severe obesity, such findings provide a starting point for providing more rational mechanism-based therapies, as has successfully been achieved for one disorder, congenital leptin deficiency.

Albright's hereditary osteodystrophy (pseudohypoparathyroidism type Ia): clinical case with a novel mutation of GNAS1

Albright's hereditary osteodystrophy is characterized by ectopic calcification and ossification, round face, short hands and feet with short terminal phalanges, short metacarpals (especially 4th and 5th) and absence of the 4th knuckle (brachydactyly type E). Here we describe a case that recently came to our attention of a girl suffering from seizures caused by hypocalcaemia, in which the clinical diagnosis of Albright's hereditary osteodystrophy and Pseudohypoparathyroidism (PHP) (Pseudohypoparathyroidism Ia) was confirmed by DNA molecular analysis. This analysis revealed a novel mutation of GNAS 1, resulting in the nonsense mutation of exon 13 (CAG-->TAG, codon 384). This result expands the spectrum of GNAS1 mutations associated with this disorder.

Molecular characterization of a cryptic 2q37 deletion in a patient with Albright hereditary osteodystrophy-like phenotype

The Albright hereditary osteodystrophy-like (AHO-like) syndrome was recently defined as a rare dysmorphic syndrome including brachymetaphalangism and mental retardation. This phenotype occurs in Albright hereditary osteodystrophy (AHO) but unlike it, the level of the Gs alpha protein activity is not reduced. To date 59 patients with these clinical and biochemical features have been reported, and for the majority of them (57/59) a cytogenetically visible 2q37 deletion has been observed. We report a new case of typical AHO-like syndrome with normal karyotype. Using the polymorphic marker D2S125 we found a loss of heterozygosity suggestive of a de novo 2q37 deletion of maternal origin. This hypothesis was confirmed by FISH analysis with a subtelomeric 2q probe containing the D2S90 marker. Genotypic analysis allowed us to map the proximal breakpoint of the subtelomeric deletion within an interval delimited by D2S2338 (present) and D2S2253 (deleted). This 2q subtelomeric deletion as small as 4 Mb is to date the smallest one observed in association with a typical AHO-like phenotype, and allows us to move the centromeric boundary of the AHO-like critical region by 750 kb towards the 2q telomere.

Minireview: GNAS: normal and abnormal functions

GNAS is a complex imprinted gene that uses multiple promoters to generate several gene products, including the G protein alpha-subunit (G(s)alpha) that couples seven-transmembrane receptors to the cAMP-generating enzyme adenylyl cyclase. Somatic activating G(s)alpha mutations, which alter key residues required for the GTPase turn-off reaction, are present in various endocrine tumors and fibrous dysplasia of bone, and in a more widespread distribution in patients with McCune- Albright syndrome. Heterozygous inactivating G(s)alpha mutations lead to Albright hereditary osteodystrophy. G(s)alpha is imprinted in a tissue-specific manner, being primarily expressed from the maternal allele in renal proximal tubules, thyroid, pituitary, and ovary. Maternally inherited mutations lead to Albright hereditary osteodystrophy (AHO) plus PTH, TSH, and gonadotropin resistance (pseudohypoparathyroidism type 1A), whereas paternally inherited mutations lead to AHO alone. Pseudohypoparathyroidism type 1B, in which patients develop PTH resistance without AHO, is almost always associated with a GNAS imprinting defect in which both alleles have a paternal-specific imprinting pattern on both parental alleles. Familial forms of the disease are associated with a mutation within a closely linked gene that deletes a region that is presumably required for establishing the maternal imprint, and therefore maternal inheritance of the mutation results in the GNAS imprinting defect. Imprinting of one differentially methylated region within GNAS is virtually always lost in pseudohypoparathyroidism type 1B, and this region is probably responsible for tissue-specific G(s)alpha imprinting. Mouse knockout models show that G(s)alpha and the alternative G(s)alpha isoform XLalphas that is expressed from the paternal GNAS allele may have opposite effects on energy metabolism in mice.