Postzygotic Somatic Mutations Research Articles

Experimental treatment of NRAS-mutated neurocutaneous melanocytosis with MEK162, a MEK-inhibitor

Neurocutaneous melanosis (NCM) is a rare congenital disorder characterized by the association of large and/or multiple congenital melanocytic nevi (CMN) of the skin with melanocytic lesions of the leptomeninges, including melanocytosis. Leptomeningeal melanocytosis carries a poor prognosis once neurological symptoms develop. Despite surgery, which is often not radical, few other treatment options exist. Recently, it was demonstrated that early embryonic, post-zygotic somatic mutations in the NRAS gene are implicated in the pathogenesis of NCM.In this report, we present a 13-year-old boy with NCM and progressive symptomatic leptomeningeal melanocytosis. A somatic NRASQ61K mutation was present in both CMN as well as the melanocytosis. Despite repeated surgery, the patient showed clinical progression. Therefore, treatment with MEK162, a MEK inhibitor, was started on compassionate use base. The patient died only five days later, i.e. too early to expect a clinical effect of MEK162 therapy. We therefore studied the effect of MEK162 at the protein level in the leptomeningeal tumor by immunohistochemical and Western Blot analyses using Ki67 and pERK antibodies. We observed lower MIB-1 expression and lower pERK expression in the post-treatment samples compared to pre-treatment, suggesting a potential effect of MEK inhibiting therapy. Further studies are needed to determine whether MEK inhibitors can effectively target NRAS-mutated symptomatic NCM, a rare but potentially fatal disease.

McCune albright syndrome with severe facial disfigurement

Introduction: McCune Albright syndrome (MAS) is a rare disease due to post zygotic somatic activating mutation in the Gs protein. It includes skin patches, bone dysplasia, and hyperfunctioning endocrinopathies. Our objective is to report an unusual disfiguring form with precocious pseudo puberty (PPP), and hot thyroid nodule. Case report: A 19 year-old girl was hospitalized for the first time at the age of 5.5 years for breast development and vaginal bleeding which began when she was 6 months old. The diagnosis was PPP due to MAS. In addition to ovarian hyperfunction, there were multifocal disfiguring bone dysplasia, and brown skin patches. As aromatase inhibitors were not available, she was treated by cyproterone acetate, which was efficient on the ovarian function, but not on bone maturation (final height: 1.35m, bone deformities, and recurrent fractures). Fortunately, bone dysplasia was stabilized under biphosphonates. But, ovarian hyper functioning relapsed, because of polycystic ovaries. Following that, a hot thyroid nodule with normal thyroid function appeared. Conclusion: This patient has MAS with severe bone dysplasia leading to a disfiguring face, hot thyroid nodule, and ovarian hyper function causing PPP then polycystic ovaries. So, in future checking for tumours development due to estrogens excess is mandatory.

A new era in the discovery of de novomutations underlying human genetic disease

Editorial text Germline mutations arise anew during meiosis in every generation. Such spontaneously occurring genetic alterations are termed de novo mutations and serve to describe those heritable mutations that neither parent possessed or transmitted. Thus, de novo mutations denote mutations that arose in the gametes of the parents as distinct from post-zygotic somatic mutations that arise during embryonic development. Studies of de novo mutations in the human genome have been very challenging owing to past technological limitations. However, the advent of highthrough put next-generation sequencing (NGS) technologies has ushered in a new era in the study of de novo mutations. Whole-genome sequencing (WGS) and whole-exome sequencing (WES) can now be performed on parentoffspring trios to identify de novo point mutations in the entire genome or within protein-coding regions, respectively [1-3]. Although genome-wide de novo copy number variants (CNVs) were previously studied using microarrays [4-7], the study of de novo point mutations or single nucleotide variants (SNVs) required the advent of largescale sequencing, which was not feasible using Sanger sequencing [1-3]. As with inherited mutations, de novo mutations range in size from point mutations and small indels of multiple bases to much larger CNVs and structural rearrangements [8]. In this article, we focus on de novo point mutations/SNVs and their implications for our understanding of the etiology of common complex diseases as well as rare Mendelian diseases. The availability of NGS has allowed first estimations of the human genome mutation rate as well as a glimpse of

Meiotic errors followed by two parallel postzygotic trisomy rescue events are a frequent cause of constitutional segmental mosaicism

Structural copy number variation (CNV) is a frequent cause of human variation and disease. Evidence is mounting that somatic acquired CNVs are prevalent, with mosaicisms of large segmental CNVs in blood found in up to one percent of both the healthy and patient populations. It is generally accepted that such constitutional mosaicisms are derived from postzygotic somatic mutations. However, few studies have tested this assumption. Here we determined the origin of CNVs which coexist with a normal cell line in nine individuals. We show that in 2/9 the CNV originated during meiosis. The existence of two cell lines with 46 chromosomes thus resulted from two parallel trisomy rescue events during postzygotic mitoses.

Pamidronic acid and cabergoline as effective long-term therapy in a 12-year-old girl with extended facial polyostotic fibrous dysplasia, prolactinoma and acromegaly in McCune-Albright syndrome: a case report

IntroductionMcCune-Albright syndrome is a complex inborn disorder due to early embryonal postzygotic somatic activating mutations in the GNAS1 gene. The phenotype is very heterogeneous and includes polyostotic fibrous dysplasia, typically involving the facial skull, numerous café-au-lait spots and autonomous hyperfunctions of several endocrine systems, leading to hyperthyroidism, hypercortisolism, precocious puberty and acromegaly.Case presentationHere, we describe a 12-year-old Caucasian girl with severe facial involvement of fibrous dysplasia, along with massive acromegaly due to growth hormone excess and precocious puberty, with a prolactinoma. Our patient was treated with a bisphosphonate and the prolactin antagonist, cabergoline, resulting in the inhibition of fibrous dysplasia and involution of both the prolactinoma and growth hormone excess. During a follow-up of more than two years, no severe side effects were noted.ConclusionTreatment with bisphosphonates in combination with cabergoline is a suitable option in patients with McCune-Albright syndrome, especially in order to circumvent surgical interventions in patients suffering from polyostotic fibrous dysplasia involving the skull base.

Genetics of bone diseases: Paget's disease, fibrous dysplasia, osteopetrosis, and osteogenesis imperfecta

Over the last few years, research into the genetics of bone diseases has produced new insights into the pathophysiology of bone remodeling. The identification of SQSTM1 mutations in Paget's disease of bone established that osteoclast activation involved both binding to ubiquitin and the proteasome pathway. However, murine models fail to replicate the full phenotype, and somatic SQSTM1 mutations have been identified, suggesting a role for complex mechanisms. In patients with fibrous dysplasia of bone, postzygotic somatic mutations in the GNAS gene are now well documented. Technological advances have improved the detection of somatic mutations in peripheral blood cells. Osteopetrosis is characterized by increased bone density due to deficient osteoclastic bone resorption. Most of the genes involved in the various clinical patterns of osteopetrosis have been identified. The identification of LRP5 gain-of-function mutations in autosomal dominant osteopetrosis type I prompted a revision of the classification scheme, and this form is now being included among the high-bone-mass diseases. Osteogenesis imperfecta is characterized by an inherited abnormality in bone formation that manifests as osteopenia with increased bone fragility. Mutations in the COL1A1 and COL1A2 genes are found in over 90% of patients. The recent identification of mutations in the CRTAP, LEPRE1, and PPIB genes in recessive forms has radically changed the classification of osteogenesis imperfecta and generated new pathophysiological hypotheses.

Mosaic Uniparental Disomies and Aneuploidies as Large Structural Variants of the Human Genome

Mosaicism is defined as the coexistence of cells with different genetic composition within an individual, caused by postzygotic somatic mutation. Although somatic mosaicism for chromosomal abnormalities is a well-established cause of developmental and somatic disorders and has also been detected in different tissues, its frequency and extent in the adult normal population are still unknown. We provide here a genome-wide survey of mosaic genomic variation obtained by analyzing Illumina 1M SNP array data from blood or buccal DNA samples of 1991 adult individuals from the Spanish Bladder Cancer/EPICURO genome-wide association study. We found mosaic abnormalities in autosomes in 1.7% of samples, including 23 segmental uniparental disomies, 8 complete trisomies, and 11 large (1.5-37 Mb) copy-number variants. Alterations were observed across the different autosomes with recurrent events in chromosomes 9 and 20. No case-control differences were found in the frequency of events or the percentage of cells affected, thus indicating that most rearrangements found are not central to the development of bladder cancer. However, five out of six events tested were detected in both blood and bladder tissue from the same individual, indicating an early developmental origin. The high cellular frequency of the anomalies detected and their presence in normal adult individuals suggest that this type of mosaicism is a widespread phenomenon in the human genome. Somatic mosaicism should be considered in the expanding repertoire of inter- and intraindividual genetic variation, some of which may cause somatic human diseases but also contribute to modifying inherited disorders and/or late-onset multifactorial traits.

Génétique des maladies osseuses

During the past years, genetics of bone disease led to a better understanding of bone remodelling pathophysiology. Thus, the discovery of SQSTM1 mutations in Paget's disease of bone has highlighted the role of ubiquitin-binding and proteasomal pathway in osteoclast activation. However, the absence of reproduction of the whole phenotype in mice models and the recent identification of somatic mutations of SQSTM1 suggest more complex mechanisms. In fibrous dysplasia of bone, the presence of post-zygotic somatic mutations of GNAS gene is now well known. Technological progresses have been accomplished to increase the detection of somatic mutations in peripheral blood. Osteopetrosis is characterized by an increased bone density due to a defect in osteoclastic resorption. Most of the genes involved in the different clinical forms are now known. The discovery of “gain of function” in the LRP5 gene in type 1 autosomal dominant osteopetrosis led to a revision of the classification, this form now belonging to the high bone mass family. Osteogenesis imperfecta is characterized by a hereditary disorder of bone formation with osteopenia and bone fragility. COL1A1 and COL1A2 genes are mutated in 90 % of cases. The recent identification of mutations in CRTAP, LEPRE1 and PPIB genes in autosomal recessive forms drastically alters the classification of this entity and opens new pathophysiological horizons.

Monozygotic Twins Discordant for Klippel-Feil Syndrome

In a pair of Japanese monozygotic twins, one manifested Klippel-Feil syndrome, a short neck with C(1-4) vertebra fusion, whereas the other was normal. The discordance between the twins suggests that Klippel-Feil syndrome results in part from a postzygotic somatic mutation or intrauterine environmental factors.

Clinical implications of genetic defects in G proteins. The molecular basis of McCune-Albright syndrome and Albright hereditary osteodystrophy.

Inactivating and activating mutations in the gene encoding G alpha s (GNAS1) are known to be the basis for 2 well-described contrasting clinical disorders, Albright hereditary osteodystrophy (AHO) and McCune-Albright syndrome (MAS). AHO is an autosomal dominant disorder due to germline mutations in GNAS1 that decrease expression or function of G alpha s protein. Loss of G alpha s function leads to tissue resistance to multiple hormones whose receptors couple to G alpha s. By contrast, MAS results from postzygotic somatic mutations in GNAS1 that lead to enhanced function of G alpha s protein. Acquisition of the activating mutation early in life leads to a more generalized distribution of the mosaicism and is associated with the classic clinical triad of polyostotic fibrous dysplasia, endocrine hyperfunction, and café au lait skin lesions described in MAS. Acquisition of a similar activating mutation in GNAS1 later in life presumably accounts for the restricted distribution of the gsp oncogene, and is associated with the development of isolated lesions (for example, fibrous dysplasia, pituitary or thyroid tumors) without other manifestations of MAS. Tissues that are affected by loss of G alpha s function in AHO are also affected by gain of G alpha s function in MAS, thus identifying specific tissues in which the second messenger cAMP plays a dominant role in cell growth, proliferation, or function. Further investigations of the functions of G alpha s and other members of the GTPase binding protein family will provide more insight into the pathogenesis and clinical manifestations of human disease.

Anatomic, Metabolic, Neuropsychological, and Molecular Genetic Studies of Three Pairs of Identical Twins Discordant for Dementia of the Alzheimer's Type

Three pairs of twins, each with proved monozygosity, were shown to be discordant for dementia of the Alzheimer's type and to have remained discordant for periods of 8 to 11 years. Dementia of the Alzheimer's type was demonstrated by history; serial clinical examinations; serial measurements of cerebral glucose utilization using positron emission tomography and of cerebral ventricular volumes and of rates of change of volumes using quantitative computed tomography; and by serial neuropsychological tests. The results of each of these measures showed no evidence of clinical abnormality in any unaffected twin. DNA markers from the proximal long arm of chromosome 21 did not distinguish between the affected and the unaffected member of any pair of identical twins. Family pedigrees were negative for Alzheimer's disease. The results suggest that environmental or other nongenetic factors contribute to Alzheimer's disease in discordant monozygotic twins, or that some cases arise by a postzygotic somatic mutation.