An activating Gs alpha mutation is present in fibrous dysplasia of bone in the McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a sporadic disease characterized by polyostotic fibrous dysplasia, café-au-lait spots, and multiple endocrinopathies. The etiology of fibrous dysplasia is unknown. Activating mutations of codon 201 in the gene encoding the alpha-subunit of Gs, the G-protein that stimulates adenylyl cyclase, have been found in all affected MAS tissues that have been studied. Initial attempts to amplify DNA from decalcified paraffin-embedded bone specimens from MAS patients were unsuccessful. Therefore, we analyzed DNA from frozen surgical bone specimens from five MAS patients using polymerase chain reaction and allele-specific oligonucleotide hybridization. Most of the cells in four specimens of dysplastic bone contained a heterozygous mutation encoding substitution of Arg201 of Gs alpha with His, but the mutation was barely detectable in peripheral blood specimens from the patients. Only a small amount of mutant allele was detected in a specimen of normal cortical bone from the fifth patient, although this patient had a high proportion of mutation in other, affected tissues. The mosaic distribution of mutant alleles is consistent with an embryological somatic cell mutation of the Gs alpha gene in MAS. The presence of an activating mutation of Gs alpha in osteoblastic progenitor cells may cause them to exhibit increased proliferation and abnormal differentiation, thereby producing the lesions of fibrous dysplasia.

A family pedigree exhibiting features of both multiple endocrine neoplasia type 1 and McCune-Albright syndromes

The multiple endocrine neoplasia (MEN) type 1 and McCune-Albright syndromes share many clinical and biochemical characteristics. This report documents for the first time the occurrence and natural history of the McCune-Albright syndrome in a female with a strong family history of MEN type 1. There may be a functional link between both of these conditions, and there is a need to look for G-protein mutations as a mechanism for disease in MEN type 1.

An unusual presentation of McCune-Albright syndrome confirmed by an activating mutation of the Gs alpha-subunit from a bone lesion

The McCune-Albright syndrome (MAS) is characterized clinically by polyostotic fibrous dysplasia, café-au-lait skin lesions, sexual precocity, and various other endocrinopathies. Recent investigations suggest an etiological role for embryonic somatic missense mutations that predict the substitution of a His or Cys for Arg at amino acid 201 of the Gs alpha-subunit (Gs alpha). Identification of these mutations in affected tissues is a sensitive assay that may help define a more complete clinical spectrum of the MAS. We investigated a woman who developed fibrous dysplasia 24 yr after premature menstruation. To determine if this was an unusual MAS variant, DNA and RNA were analyzed from affected and unaffected tissues. From samples of affected rib and normal rib DNA was extracted, amplified by polymerase chain reaction, subcloned, and sequenced. RNA was extracted from affected bone, reverse transcribed, amplified by polymerase chain reaction, subcloned, and sequenced. DNA sequence predicting a His for Arg substitution at Gs alpha amino acid 201 was found in 47% of the recombinant plasmids from DNA of affected bone and 17% of the plasmids from DNA of unaffected bone; a significant (P < 0.05) difference in frequency. The His201 substitution was found in 42% of the recombinant plasmids from RNA of affected bone. We conclude that this clinical variant is qualitatively indistinguishable from presentations of the complete MAS.

Melanotic macules following Blaschko's lines in McCune-Albright syndrome

Hyperpigmented macules are a characteristic feature of neurofibromatosis and the McCune-Albright syndrome. Whereas neurofibromatosis 1 has an autosomal dominant mode of inheritance, it has been suggested that McCune-Albright syndrome is the result of a lethal gene surviving by mosaicism. Recent molecular studies have supported this concept by providing evidence of a somatic mutation of the gene encoding the G protein. We report two patients with McCune-Albright syndrome whose melanotic macules show a clear relation to the lines of Blaschko. The lines of Blaschko are thought to represent the dorso-ventral outgrowth of two different cell populations during embryogenesis, thus reflecting genetic mosaicism. A survey of published photographs of patients with McCune-Albright syndrome in the literature revealed additional cases with macules following Blaschko's lines. In other cases, the configuration of the macules was reminiscent of the flag-like rectangular pattern of pigmentation found in human chimaeras. A very early somatic mutation may have similar effects on the pigmentation pattern as a chimaeric state, which is the result of the double fertilization of an ovum. Café-au-lait spots in 10 of our own patients with neurofibromatosis 1 could not be associated with either Blaschko's lines or the rectangular pattern of pigmentation in chimaeras. We conclude that, in contrast with the café-au-lait spots in autosomal dominant neurofibromatosis 1, the configuration pattern of melanotic macules in McCune-Albright syndrome in many cases characteristically reflects the mosaic state of the organism.

G protein mutations in human disease

The heterotrimeric G proteins couple cell-surface receptors for extracellular signals to intracellular effectors that generate second messengers. Abnormal G protein signalling, resulting from posttranslational modifications by bacterial toxins, altered gene expression, or gene mutations, may lead to diverse biological consequences. Mutations within G protein alpha subunit genes that lead to either constitutive activation or loss of function have been identified. Such G protein mutations play a role in the pathogenesis of several human diseases, including sporadic endocrine tumors, McCune-Albright syndrome, and Albright hereditary osteodystrophy.

Severe endocrine and nonendocrine manifestations of the McCune-Albright syndrome associated with activating mutations of stimulatory G protein GS

McCune-Albright syndrome (MCAS) is a sporadic disease classically including polyostotic fibrous dysplasia, café au lait spots, sexual precocity, and other hyperfunctional endocrinopathies. An activating missense mutation in the gene for the alpha subunit of GS, the G protein that stimulates cyclic adenosine monophosphate formation, has been reported to be present in these patients. The mutation is found in variable abundance in different affected endocrine and nonendocrine tissues, consistent with the mosaic distribution of abnormal cells generated by a somatic cell mutation early in embryogenesis. We describe three patients with MCAS who had profound endocrine and nonendocrine disease and who died in childhood. Two of the patients were severely ill neonates whose complex symptoms did not immediately suggest MCAS. A mutation of residue Arg201 of GS alpha was found in affected tissues from all three children. A review of the literature and unpublished case histories emphasizes the existence of other patients with severe and unusual clinical manifestations. We conclude that the manifestations of MCAS are more extensive than is generally appreciated, and may include hepatobiliary disease, cardiac disease, other nonendocrine abnormalities, and sudden or premature death.

Identification of a mutation in the gene encoding the alpha subunit of the stimulatory G protein of adenylyl cyclase in McCune-Albright syndrome

McCune-Albright syndrome (MAS) is characterized by polyostotic fibrous dysplasia, café-au-lait lesions, and a variety of endocrine disorders, including precocious puberty, hyperthyroidism, hypercortisolism, growth hormone excess, and hyperprolactinemia. The diverse metabolic abnormalities seen in MAS share the involvement of cells that respond to extracellular signals through activation of the hormone-sensitive adenylyl cyclase system (EC 4.6.1.1). Mutations that lead to constitutive activation of Gs alpha, the guanine nucleotide-binding regulatory protein that stimulates adenylyl cyclase activity, have been identified in a subset of human growth hormone-secreting pituitary tumors and human thyroid tumors. We report here the identification of a mutation in the gene encoding Gs alpha in a patient with MAS. Denaturing gradient gel electrophoresis was used to analyze amplified DNA fragments including exon 8 or exon 9 of the Gs alpha gene. In one subject with MAS a G-to-A transition was found in exon 8 of one of the two alleles encoding Gs alpha. This single-base substitution results in the replacement of arginine by histidine at position 201 of the mature Gs alpha protein. Semiquantitative analysis of amplified DNA indicated that the mutant allele was less prevalent than the wild-type allele in peripheral leukocytes and was present in very low levels in skin. These findings support the previous contention that the segmental distribution and variable expression of the cutaneous, skeletal, and endocrine manifestations of MAS reflect an underlying somatic mosaicism. Further, these results suggest that the molecular basis of MAS is a postzygotic mutation in Gs alpha that causes constitutive activation of adenylyl cyclase.

Activating mutations of the stimulatory G protein in the McCune-Albright syndrome

BACKGROUND

The McCune-Albright syndrome is a sporadic disease characterized by polyostotic fibrous dysplasia, café au lait spots, sexual precocity, and hyperfunction of multiple endocrine glands. These manifestations may be explained by a somatic mutation in affected tissues that results in activation of the signal-transduction pathway generating cyclic AMP (cAMP). We analyzed DNA from tissues of patients with the McCune-Albright syndrome for the presence of activating mutations of the gene for the alpha subunit of the G protein (Gs alpha) that stimulates cAMP formation.

METHODS

Genomic DNA fragments encompassing regions (exons 8 and 9) previously found to contain activating missense mutations of the Gs alpha gene (gsp mutations) in sporadically occurring pituitary tumors were amplified in tissues from four patients with the McCune-Albright syndrome by the polymerase chain reaction. The amplified DNA was analyzed for mutations by denaturing gradient gel electrophoresis and allele-specific oligonucleotide hybridization.

RESULTS

We detected one of two activating mutations within exon 8 of the Gs alpha gene in tissues from all four patients, including affected endocrine organs (gonads, adrenal glands, thyroid, and pituitary) and tissues not classically involved in the McCune-Albright syndrome. In two of the patients, histidine was substituted for arginine at position 201 of Gs alpha, and in the other two patients cysteine was substituted for the same arginine residue. In each patient the proportion of cells affected varied from tissue to tissue. In two endocrine organs, the highest proportion of mutant alleles was found in regions of abnormal cell proliferation.

CONCLUSIONS

Mutations within exon 8 of the Gs alpha gene that result in increased activity of the Gs protein and increased cAMP formation are present in various tissues of patients with the McCune-Albright syndrome. Somatic mutation of this gene early in embryogenesis could result in the mosaic population of normal and mutant-bearing tissues that may underlie the clinical manifestations of this disease.

Monozygotic twins discordant for the major signs of McCune-Albright syndrome

We describe a girl, one of monozygotic (MZ) twins, with endocrine dysfunction with precocious puberty, café-au-lait nevi and polyostotic fibrous dysplasia (PFD), McCune-Albright syndrome (MAS). After treatment with cyproterone acetate for 7 years the precocious puberty and excess growth improved but the bone-age still remain advanced. The co-twin had an advanced bone-age and a small café-au-lait spot, but showed neither endocrinopathy nor fibrous dysplasia of bone. On the basis of the findings in these twins, together with those in previously reported familial cases of MAS, including two pairs of MZ twins, a 2-hit mutation hypothesis is proposed: a dominant mutation may be inherited and leads to PFD in offspring as the primary defect of MAS; the second mutation may occur in somatic cell leading to mosaicism and thus resulting in MAS. This concept explains not only sporadic cases of MAS but also reported familial cases. If we assume that the second mutation occurred in an early somatic division, it would explain the discrepancy of clinical manifestation between MZ twins.

G protein Gs alpha (GNAS 1), the probable candidate gene for Albright hereditary osteodystrophy, is assigned to human chromosome 20q12-q13.2

Guanine nucleotide-binding proteins, also known as G proteins, mediate intracellular responses to a wide variety of extracellular stimuli. A variety of genes that specify the synthesis of the components of guanine nucleotide proteins have been identified. One of these proteins, termed Gs alpha (GNAS1), is the G protein component of the olfactory signal transduction cascade. Mutations in the GNAS1 gene leading to Gs alpha protein deficiency are known to be associated with pseudohypoparathyroidism Ia (Albright hereditary osteodystrophy) and certain pituitary tumors with acromegaly. Studies on the human--mouse somatic cell hybrids provisionally assigned this gene to chromosome 20. We have now confirmed this localization on chromosome 20 and regionally assigned the GNAS1 gene to 20q12-q13.2 by in situ hybridization.

Fibrous dysplasia and cherubism as an hereditary familial disease. Follow-up of four generations

Five cases of dysplasia of the jaws in one family which has been under our observation since 1970 are reported. The disease appeared as a mixed display of jaw lesions, in some members as fibrous dysplasia and in others as cherubism. We were able to trace the disorder through an unbroken line of four generations, and thus to demonstrate autosomal dominant inheritance. Cytogenetic analysis performed on three members of this family revealed a significantly increased rate of chromosomal breakage.

[Type I pseudohypoparathyroidism. Study and prolonged follow-up of a case]

The prolonged evolution of a case of pseudohypoparathyroidism with hereditary osteodystrophy (AHO) and osteitis fibrosa is presented. The diagnosis was confirmed by the existence of a peculiar phenotype, hypocalcaemia, hyperphosphatemia, increased PTH values, and a lack of tubular response after PTH and radiological signs of hyperparathyroidism. The clinical and biochemical evolution, under 1.25 (OH)2D3 therapy with special emphasis on the growth and development were shown. The bibliography was also reviewed.

Lethal genes surviving by mosaicism: a possible explanation for sporadic birth defects involving the skin

A genetic concept is advanced to explain the origin of several sporadic syndromes characterized by a mosaic distribution of skin defects. It is postulated that these disorders are due to the action of a lethal gene surviving by mosaicism. The presence of the mutation in the zygote will lead to death of the embryo at an early stage of development. Cells bearing the mutation can survive only in a mosaic state, in close proximity with normal cells. The mosaic may arise either from a gametic half chromatid mutation or from an early somatic mutation. This concept of origin is proposed to apply to the Schimmelpenning-Feuerstein-Mims syndrome, the McCune-Albright syndrome, the Klippel-Trenaunay syndrome, the Sturge-Weber syndrome, and neurocutaneous melanosis. Moreover, this etiologic hypothesis may apply to two other birth defects that have recently been delineated, the Proteus syndrome (partial gigantism of hands or feet, hemihypertrophy, macrocephaly, linear papillomatous epidermal nevus, subcutaneous hemangiomas and lipomas, accelerated growth, and visceral anomalies), and the Delleman-Oorthuys syndrome (orbital cyst, porencephaly, periorbital appendages, and focal aplasia of the skin.

Neurofibromatosis and Albright's syndrome

For both NF and Albright's syndrome, the pathogenetic relationships between the various elements of the respective syndromes remain a mystery, and the importance of nontumorous endocrine abnormalities in neurofibromatosis has, in my opinion, been overstated. Nonetheless, the parallel between the two disorders is striking, and the consistent occurrence of skin and skeletal dyplasias in both suggests that a search for the fundamental defect in either can be advanced by focusing on what is common to these two types of tissue. For example, how does one reconcile a disturbance of the melanosome with skeletal aberrations? An answer to that question will put us on the right track. One final question must be asked. Are neurofibromatosis and Albright's syndrome alternate manifestations of the same disorder? In a trivial sense, the answer may be yes. That is, in at least some instances, one condition may have been mistaken for the other, and thus a factitious overlap or "sameness" misconstrued. Upon closer scrutiny, however, there are two important points that would cast doubt on a positive response to this question: Neurofibromatosis, or at least neurofibromatosis I, is heritable as an autosomal dominant trait, whereas heritability has not been documented for Albright's syndrome; and I am unaware of reported cases that describe both disorders, diagnosed by criteria beyond café au lait spots and bone dysplasia, in one and the same individual, although such a case has been shared with me by S. A. Sorensen, M.D., of the Genetics Institute of Copenhagen, Denmark. The full reporting of such a case would be of great interest.

Cranial sclerosis with striated bone disease (osteopathia striata)

This report concerns another case of striped bone disease (Osteopathia striata) together with sclerosis of the base of the skull. The mode of inheritance of this rare genetic disorder is still unknown. The clinical characteristics of 20 cases reported in the international literature are summarized and compared with our own findings.

The McCune-Albright syndrome: a lethal gene surviving by mosaicism

In the McCune-Albright syndrome, fibrous dysplasia of bones and various forms of endocrine dysfunction are associated with multiple pigmented skin lesions. Examination of a 4-year-old female patient and comparison with photographs published in the literature revealed that the cutaneous pigmentation is arranged in a systematized pattern following the lines of Blaschko. Apparently, this pattern visualizes the dorso-ventral outgrowth of two different populations of cells during early embryogenesis. As all cases of the syndrome are sporadic, it is postulated that the disease is caused by an autosomal "dominant" lethal gene, leading to loss of the zygote in utero. Cells bearing the mutation can only survive when they are intermingled with normal cells. The mosaic may arise either from a gametic half chromatid mutation, or from an early somatic mutation. This concept offers an explanation for the scattered asymmetric distribution of bone lesions, and for the observation that the endocrinopathy may be either of central or peripheral origin, according to the random distribution of the mutant population of cells.

A probable monogenic form of polyostotic fibrous dysplasia

A 37 year-old female patient with polyostotic fibrous dysplasia (PFD) is described. She presented the typical "café au lait" spots and severe bone involvement including a maxillary osteosarcoma. The father, four sibs, two nephews, two paternal aunts and two paternal first cousins were clinically examined, and seven of them also radiologically evaluated. "Café au lait" spots were found in the father, three sibs, one nephew, one aunt and one first cousin. Although no definite PFD bone lesions, mild radiological abnormalities were found in the father, three sibs and one nephew. These findings were interpreted as the variable expression of a pleiotropic gene. The present observation and three previous familial cases of this entity strongly suggest the existence of a form of PFD determined by an autosomal dominant gene.

Osteosarcoma, fibrous dysplasia, and a chromosomal abnormality in a 3-year-old child

Osteosarcoma is a type of malignant bone tumor that is rare among children less than five years old. This report describes a 3-year-old boy with osteosarcoma of the right proximal femur and polyostotic fibrous dysplasia of the right femur and tibia. After hemipelvectomy, histologic examination of the amputated limb disclosed that the osteosarcoma had developed in a focus of fibrous dysplasia. Cytogenetic analysis of the patient's blood lymphocytes revealed a 4q-/7p + translocation in all cells. The patient's mother had an identical translocation but did not have a history of osteosarcoma or evidence of fibrous dysplasia. The chromosomal abnormality and the developmental osseous disorder may have predisposed this patient to developing osteosarcoma at an exceptionally young age.

Albright's hereditary osteodystrophy

The authors observed different clinical forms of Albright's hereditary osteodystrophy in 4 members of a family (two sisters, their mother and the maternal grandfather). The sisters were affected by pseudohypoparathyroidism type I, the older manifested the hypocalcemic variety, the younger the normocalcemic variety; the mother and the grandfather presented only with short stature and subcutaneous calcifications. The variety of clinical and biochemical alterations observed in these 3 generations supports evidence that Albright's hereditary osteodystrophy has a broad spectrum and that distinctions between the various forms of pseudohypoparathyroidsim should not be rigidly considered.

Familial polyostotic fibrous dysplasia

A case of polyostotic fibrous dysplasia of the craniofacial type is presented, together with substantial evidence that this condition had a genetic basis in this patient. A review of the literature indicates that there is absolutely no previous evidence of a genetic basis to this condition. The possibility that the propositus suffered from polyostotic fibrous dysplasia of the Jaffe or the Albright type was excluded.