Somatic Mosaicisms Research Articles

First report of ATP2A2 somatic mosaicism occurring during embryogenesis in transient acantholytic dermatosis

AbstractTransient acantholytic dermatosis (TAD) is a relatively common skin disease that typically affects older individuals, which shows clinical and histologic similarities to autosomal dominant Darier disease. TAD was recently shown to be caused by somatic ATP2A2 damaging variants. In this study, we performed Sanger sequencing and droplet digital PCR (ddPCR) in a Japanese elderly male with TAD to identify ATP2A2 somatic mosaicism occurring during embryogenesis for the first time and mutant allelic fraction (MAF). Sanger sequencing revealed a known heterozygous substitution c.1645C>T, p.Arg549* in ATP2A2 from blood and the affected skin containing the epidermis and dermis, whereas the signals of the mutated allele were weaker, suggesting that discrepancy of signal intensities demonstrates the presence of somatic mosaicism. By ddPCR, the normal and mutant allele were identified in genomic DNAs and the MAFs were 20.1% (affected skin) and 14.7% (blood), respectively. In the present case, somatic mosaicisms observed in ectodermal (epidermis) and mesodermal (dermis and blood) origin DNA can be explained by a mutational event during the early‐stage differentiation of embryonic epiblast in embryogenesis, and mutant embryonic cells somewhat preferentially differentiate to form the epidermis, rather than the dermis and blood. Disrupted intracellular Ca2+ homoeostasis through clinical deterioration together with ATP2A2 somatic mosaicism in this patient might result in transient skin eruptions.

Is There Any Mosaicism in REarranged During Transfection Variant in Hirschsprung Disease’s Patients?

BackgroundHirschsprung disease (HSCR) is a heterogeneous genetic disease characterized by the absence of ganglion cells in the intestinal tract. The REarranged during Transfection (RET) is the most responsible gene for its pathogenesis. RET’s somatic mosaicisms have been reported for HSCR; however, they are still under-recognized. Therefore, we determined the frequency of somatic mutation of RET rs2435357 in HSCR patients at our institution.MethodsWe performed RET rs2435357 genotyping from 73 HSCR formalin-fixed and paraffin-embedded (FFPE) rectal and 60 non-HSCR controls using the PCR-RFLP method. Subsequently, we compared those frequencies of genotypes for RET rs2435357 with our previous genotyping data from 93 HSCR blood specimens.ResultsThe frequencies of genotypes for RET rs2435357 in HSCR paraffin-embedded rectal were CC 0, CT 11 (15%), and TT 62 (85%), whereas their frequencies in HSCR blood samples were CC 4 (4.3%), CT 22 (23.7%), and TT 67 (72%). Those frequencies differences almost reached a significant level (p = 0.06). Moreover, the frequency of RET rs2435357 risk allele (T) was significantly higher in HSCR patients (135/146, 92.5%) than controls (46/120, 38.3%) (p = 3.4 × 10–22), with an odds ratio of 19.74 (95% confidence interval = 9.65–40.41).ConclusionOur study suggests somatic mosaicism in HSCR patients. These findings further imply the complexity of the pathogenesis of HSCR. Moreover, our study confirms the RET rs2435357 as a significant genetic risk factor for HSCR patients.

L’esofagite eosinofila: quando deglutire diventa difficile

Knowledge in the genetic field of autoinflammatory diseases has progressively increased over the last decade. Starting from the genetic knowledge on a few initially known diseases (Familial Mediterranean Fever, Periodic Syndrome Associated with Tumor Necrosis Factor Receptor 1, Mevalonate Kinase Deficiency, Cryopyrinopathies), at least 40 genes associated with these conditions have been identified, and more than 100 genes are currently being tested with Next Generation Sequencing (NGS) technologies. Indeed, starting recommendations for the genetic diagnosis of autoinflammatory diseases were limited to a gene-by-gene diagnosis strategy, based on the Sanger method, and restricted to a few prototypic recurrent fevers. More recently, improvement of genetic technologies, in particular NGS, allowed identification of genetic variants among involved genes in an easier and more rapid way. Detection of more and more genetic variants made interpretation of results more complicated, and often a genetic diagnosis is not achieved. On the other hand, other mechanisms, namely somatic mosaicisms, epigenetic modifications, digenic inheritance, allow to explain some not genetically defined cases. Eventually, further genetic and non-genetic mechanisms will be probably identified in near future to explain underlying basis of autoinflammatory diseases, especially in a still large part of patients without a clearcut genetic basis.

Factors Regulating the Activity of LINE1 Retrotransposons.

LINE-1 (L1) is a class of autonomous mobile genetic elements that form somatic mosaicisms in various tissues of the organism. The activity of L1 retrotransposons is strictly controlled by many factors in somatic and germ cells at all stages of ontogenesis. Alteration of L1 activity was noted in a number of diseases: in neuropsychiatric and autoimmune diseases, as well as in various forms of cancer. Altered activity of L1 retrotransposons for some pathologies is associated with epigenetic changes and defects in the genes involved in their repression. This review discusses the molecular genetic mechanisms of the retrotransposition and regulation of the activity of L1 elements. The contribution of various factors controlling the expression and distribution of L1 elements in the genome occurs at all stages of the retrotransposition. The regulation of L1 elements at the transcriptional, post-transcriptional and integration into the genome stages is described in detail. Finally, this review also focuses on the evolutionary aspects of L1 accumulation and their interplay with the host regulation system.

A late-onset male Fabry disease patient with somatic mosaicism of a classical GLA mutation: a case report

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the α-galactosidase A gene (GLA). Male patients of FD develop early sign and symptoms in childhood or adolescence. However, "de novo somatic mosaicism" is rare and might be developed a relatively mild phenotype despite carrying a classic type. A 34-year-old male patient visited with foamy urine. Renal biopsy findings were consistent with FD. Leukocyte α-galactosidase activity was markedly reduced at 5.3 nmol/hr/mg (normal range, 25-126). Sequence analysis of the patient's GLA gene identified mosaicism for the mutation GLA[NM_000169.2] c.820=/G>C. This mutation results in a substitution of the amino acid in position 274 from glycine to arginine. However, no family members showed FD-related symptoms, and the daughter of the patient was also tested for paternity and was identified as a real biological daughter, but DNA sequence analysis for FD showed no mutations. Based on these results, we diagnosed the patients as de novo mutation with somatic mosaicism. Next generation sequencing turned out that 58% of the readings had the mutated allele in buccal cells, 84% in blood, and 85% in urine, when 100% should be expected in a hemizygous affected male confirming the presence of somatic mosaicisms. The patient has been on treatment for enzyme replacement therapy (agalsidase-β, 1.0 mg/kg biweekly) for past 9 years and has maintained normal renal function (serum creatinine 1.0 mg/dL) with mild albuminuria (123 mg/g Cr). Therefore, this case suggests somatic mosaicism is one of important phenotype modifiers.

Management of Monogenic IL-1 Mediated Autoinflammatory Diseases in Childhood.

Monogenic Interleukin 1 (IL-1) mediated autoinflammatory diseases (AID) are rare, often severe illnesses of the innate immune system associated with constitutively increased secretion of pro-inflammatory cytokines. Clinical characteristics include recurrent fevers, inflammation of joints, skin, and serous membranes. CNS and eye inflammation can be seen. Characteristically, clinical symptoms are coupled with elevated inflammatory markers, such as C-reactive protein (CRP) and serum amyloid A (SAA). Typically, AID affect infants and children, but late-onset and atypical phenotypes are described. An in-depth understanding of autoinflammatory pathways and progress in molecular genetics has expanded the spectrum of AID. Increasing numbers of genetic variants with undetermined pathogenicity, somatic mosaicisms and phenotype variability make the diagnosis of AID challenging. AID should be diagnosed as early as possible to prevent organ damage. The diagnostic approach includes patient/family history, ethnicity, physical examination, specific functional testing and inflammatory markers (SAA, CRP) during, and in between flares. Genetic testing should be performed, when an AID is suspected. The selection of genetic tests is guided by clinical findings. Targeted and rapid treatment is crucial to reduce morbidity, mortality and psychosocial burden after an AID diagnosis. Management includes effective treat-to-target therapy and standardized, partnered monitoring of disease activity (e.g., AIDAI), organ damage (e.g., ADDI), patient/physician global assessment and health related quality of life. Optimal AID care in childhood mandates an interdisciplinary team approach. This review will summarize the current evidence of diagnosing and managing children with common monogenic IL-1 mediated AID.

Diagnosis and Management of the Cryopyrin-Associated Periodic Syndromes (CAPS): What Do We Know Today?

The cryopyrin-associated periodic syndromes (CAPS) are usually caused by heterozygous NLRP3 gene variants, resulting in excessive inflammasome activation with subsequent overproduction of interleukin (IL)-1β. The CAPS spectrum includes mild, moderate, and severe phenotypes. The mild phenotype is called familial cold autoinflammatory syndrome (FCAS), the moderate phenotype is also known as Muckle–Wells syndrome (MWS), and the neonatal-onset multisystem inflammatory disease (NOMID)/chronic infantile neurologic cutaneous articular syndrome (CINCA) describes the severe phenotype. The CAPS phenotypes display unspecific and unique clinical signs. Dermatologic, musculoskeletal, ocular, otologic, and neurologic disease symptoms combined with chronic systemic inflammation are characteristic. Nevertheless, making the CAPS diagnosis is challenging as several patients show a heterogeneous multi-system clinical presentation and the spectrum of genetic variants is growing. Somatic mosaicisms and low-penetrance variants lead to atypical clinical symptoms and disease courses. To avoid morbidity and to reduce mortality, early diagnosis is crucial, and a targeted anti-IL-1 therapy should be started as soon as possible. Furthermore, continuous and precise monitoring of disease activity, organ damage, and health-related quality of life is important. This review summarizes the current evidence in diagnosis and management of patients with CAPS.

The Effects of Single Nucleotide Polymorphisms in Cancer RNAi Therapies.

Simple SummaryDespite the recent progress in RNAi delivery of siRNA-based therapeutics for cancer therapy, the presence of single nucleotide polymorphisms (SNPs) in the general population could dramatically reduce the effectiveness of RNAi therapy. Their ubiquitous presence can also lead to unpredictable and adverse side effects. Because both SNPs and somatic mosaicisms have also been implicated in a number of human diseases including cancer, however, these specific changes offer the ability to selectively and efficiently target cancer cells. Here, we discuss how SNPs influence the development and success of novel anticancer RNAi therapies.Tremendous progress in RNAi delivery methods and design has allowed for the effective development of siRNA-based therapeutics that are currently under clinical investigation for various cancer treatments. This approach has the potential to revolutionize cancer therapy by providing the ability to specifically downregulate or upregulate the mRNA of any protein of interest. This exquisite specificity, unfortunately, also has a downside. Genetic variations in the human population are common because of the presence of single nucleotide polymorphisms (SNPs). SNPs lead to synonymous and non-synonymous changes and they occur once in every 300 base pairs in both coding and non-coding regions in the human genome. Much less common are the somatic mosaicism variations associated with genetically distinct populations of cells within an individual that is derived from postzygotic mutations. These heterogeneities in the population can affect the RNAi’s efficacy or more problematically, which can lead to unpredictable and sometimes adverse side effects. From a more positive viewpoint, both SNPs and somatic mosaicisms have also been implicated in human diseases, including cancer, and these specific changes could offer the ability to effectively and, more importantly, selectively target the cancer cells. In this review, we discuss how SNPs in the human population can influence the development and success of novel anticancer RNAi therapies and the importance of why SNPs should be carefully considered.

Exploratory analysis of transposable elements expression in the C. elegans early embryo

BackgroundTransposable Elements (TE) are mobile sequences that make up large portions of eukaryote genomes. The functions they play within the complex cellular architecture are still not clearly understood, but it is becoming evident that TE have a role in several physiological and pathological processes. In particular, it has been shown that TE transcription is necessary for the correct development of mice embryos and that their expression is able to finely modulate transcription of coding and non-coding genes. Moreover, their activity in the central nervous system (CNS) and other tissues has been correlated with the creation of somatic mosaicisms and with pathologies such as neurodevelopmental and neurodegenerative diseases as well as cancers.ResultsWe analyzed TE expression among different cell types of the Caenorhabditis elegans (C. elegans) early embryo asking if, where and when TE are expressed and whether their expression is correlated with genes playing a role in early embryo development. To answer these questions, we took advantage of a public C. elegans embryonic single-cell RNA-seq (sc-RNAseq) dataset and developed a bioinformatics pipeline able to quantify reads mapping specifically against TE, avoiding counting reads mapping on TE fragments embedded in coding/non-coding transcripts. Our results suggest that i) canonical TE expression analysis tools, which do not discard reads mapping on TE fragments embedded in annotated transcripts, may over-estimate TE expression levels, ii) Long Terminal Repeats (LTR) elements are mostly expressed in undifferentiated cells and might play a role in pluripotency maintenance and activation of the innate immune response, iii) non-LTR are expressed in differentiated cells, in particular in neurons and nervous system-associated tissues, and iv) DNA TE are homogenously expressed throughout the C. elegans early embryo development.ConclusionsTE expression appears finely modulated in the C. elegans early embryo and different TE classes are expressed in different cell types and stages, suggesting that TE might play diverse functions during early embryo development.

Detection of Solid Tumor Molecular Residual Disease(MRD) Using Circulating Tumor DNA (ctDNA).

Circulating tumor DNA (ctDNA) is a component of cell-free DNA that is shed by malignant tumors into the bloodstream and other bodily fluids. Levels of ctDNA are typically low, particularly in patients with localized disease, requiring highly sophisticated methods for detection and quantification. Multiple liquid biopsy methods have been developed for ctDNA analysis in solid tumor malignancies and are now enabling detection and assessment of earlier stages of disease, post-treatment molecular residual disease (MRD), resistance to targeted systemic therapy, and tumor mutational burden. Understanding ctDNA biology, mechanisms of release, and clearance and size characteristics, in conjunction with the application of molecular barcoding and targeted error correction, have increased the sensitivity and specificity of ctDNA detection techniques. Combinatorial approaches including integration of ctDNA data withcirculating protein biomarkers may further improve assay sensitivity and broaden the scope of ctDNA applications. Circulating viral DNA may be utilized to monitor disease in some virally induced malignancies. In spite of increasingly accurate methods of ctDNA detection, results need to be interpreted with caution given that somatic mosaicisms such as clonal hematopoiesis of indeterminate potential (CHIP) may give rise to genetic variants in the bloodstream unrelated to solid tumors, and the limited concordance observed between different commercial platforms. Overall, highly precise ctDNA detection and quantification methods have the potential to transform clinical practice via non-invasive monitoring of solid tumor malignancies, residual disease detection at earlier timepoints than standard clinical and/or imaging surveillance, and treatment personalization based on real-time assessment of the tumor genomic landscape.

Somatic mosaicisms of chromosome 1 at two different stages of ontogenetic development detected by Rh blood group discrepancies.

Spontaneous Rh blood group changes are a striking sign, reported to occur mainly in patients with hematologic disorders. Upon routine blood grouping, 2 unrelated individuals showed unexplained mixed red cell phenotype regarding the highly immunogenic c antigen (RH4), clinically relevant for blood transfusion and fetomaternal incompatibility. About half of their red cells were c-positive, whereas the other half were c-negative. These apparently hematologically healthy females had no history of transfusion or transplantation, and they tested negative for chimerism. Genotyping of flanking chromosome 1 microsatellites in blood, finger nails, hair, leukocyte subpopulations, and erythroid progenitor cells showed partial loss of heterozygosity encompassing the RHD/RHCE loci, spanning a 1p region of 26.7 or 42.4 Mb, respectively. Remarkably, in one case this was detected in all investigated tissues, whereas in the other, exclusively myeloid cells showed loss of heterozygosity. Both carried the RhD-positive haplotypes CDe and the RhD-negative haplotype cde. RHD/RHCE genotypes of single erythroid colonies and dual-color fluorescent in situ hybridization analyses indicated loss of the cde haplotype and duplication of the CDe haplotype in the altered cell line. Accordingly, red cell C antigen (RH2) levels of both propositae were higher than those of heterozygous controls. Taken together, the Rhc phenotype splitting appeared to be caused by deletion of a part of 1p followed by duplication of homologous stretches of the sister chromosome. In one case, this phenomenon was confined to myeloid stem cells, while in the other, a pluripotent stem cell line was affected, demonstrating somatic mosaicism at different stages of ontogenesis.

Partial androgen insensitivity syndrome due to somatic mosaicism of the androgen receptor

Androgen insensitivity syndrome (AIS) is the most frequent etiology of 46,XY disorders of sex development (DSDs), and it is an X-linked disorder caused by mutations in the androgen receptor (AR) gene. AIS patients present a broad phenotypic spectrum and individuals with a partial phenotype present with different degrees of undervirilized external genitalia. There are more than 500 different AR gene allelic variants reported to be linked to AIS, but the presence of somatic mosaicisms has been rarely identified. In the presence of a wild-type AR gene, a significant degree of spontaneous virilization at puberty can be observed, and it could influence the gender assignment, genetic counseling and the clinical and psychological management of these patients and the psychosexual outcomes of these patients are not known. In this study, we report two patients with AR allelic variants in heterozygous (c.382G>T and c.1769-1G>C) causing a partial AIS (PAIS) phenotype. The first patient was raised as female and she had undergone a gonadectomy at puberty. In both patients there was congruency between gender of rearing and gender identity and gender role. Somatic mosaicism is rare in AIS and nonsense AR variant allelic can cause partial AIS phenotype in this situation. Despite the risk of virilization and prenatal androgen exposure, the gender identity and gender role was concordant with sex of rearing in both cases. A better testosterone response can be expected in male individuals and this should be considered in the clinical management.

Mosaicism and prenatal diagnosis options: insights from retinoblastoma.

In sporadic cases, a post-zygotic mutational event signifies a somatic mosaicism in the affected child only, which implies that these mutations affect only a portion of the body. Therefore siblings do not need follow-up. On the other hand, a pre-zygotic mutation transmitted by an unaffected mosaic parent implies recurrent risks in offspring. To better estimate the contribution of pre- and post-zygotic events, we analysed 124 consecutive bilateral retinoblastoma probands, carrying a heterozygous RB1 pathogenic variant and their unaffected, non-carrier parents. In order to evaluate somatic mosaicism in blood, the deleterious RB1 pathogenic variant identified in the proband, was searched for in the unaffected parents, using targeted deep sequencing. Observed recurrences, which represent an estimation of germline and somatic mosaicisms, were recorded and computed in the sibships. Deep sequencing revealed one mosaic-unaffected parent out of 124 tested couples, which provides an estimation of the maximal risk of recurrence, due to parental mosaicism, at 0.4%. Follow-up in the sibships showed one recurrence, providing a maximal recurrence risk, due to parental mosaicism, at 0.8%. Two different statistical strategies led to close estimates (0.4 and 0.8% risks) which appeared 266-533-fold higher, as compared with the general population. These recurrence estimates could be considered when counselling couples with retinoblastoma or diseases with a high de novo mutation rate.

Letter to the Editor: Hypothesis: Somatic Mosaicism and Parkinson Disease.

Letter to the Editor: Hypothesis: Somatic Mosaicism and Parkinson Disease.

Phenotypic and molecular insights into CASK-related disorders in males.

BackgroundHeterozygous loss-of-function mutations in the X-linked CASK gene cause progressive microcephaly with pontine and cerebellar hypoplasia (MICPCH) and severe intellectual disability (ID) in females. Different CASK mutations have also been reported in males. The associated phenotypes range from nonsyndromic ID to Ohtahara syndrome with cerebellar hypoplasia. However, the phenotypic spectrum in males has not been systematically evaluated to date.MethodsWe identified a CASK alteration in 8 novel unrelated male patients by targeted Sanger sequencing, copy number analysis (MLPA and/or FISH) and array CGH. CASK transcripts were investigated by RT-PCR followed by sequencing. Immunoblotting was used to detect CASK protein in patient-derived cells. The clinical phenotype and natural history of the 8 patients and 28 CASK-mutation positive males reported previously were reviewed and correlated with available molecular data.ResultsCASK alterations include one nonsense mutation, one 5-bp deletion, one mutation of the start codon, and five partial gene deletions and duplications; seven were de novo, including three somatic mosaicisms, and one was familial. In three subjects, specific mRNA junction fragments indicated in tandem duplication of CASK exons disrupting the integrity of the gene. The 5-bp deletion resulted in multiple aberrant CASK mRNAs. In fibroblasts from patients with a CASK loss-of-function mutation, no CASK protein could be detected. Individuals who are mosaic for a severe CASK mutation or carry a hypomorphic mutation still showed detectable amount of protein.ConclusionsBased on eight novel patients and all CASK-mutation positive males reported previously three phenotypic groups can be distinguished that represent a clinical continuum: (i) MICPCH with severe epileptic encephalopathy caused by hemizygous loss-of-function mutations, (ii) MICPCH associated with inactivating alterations in the mosaic state or a partly penetrant mutation, and (iii) syndromic/nonsyndromic mild to severe ID with or without nystagmus caused by CASK missense and splice mutations that leave the CASK protein intact but likely alter its function or reduce the amount of normal protein. Our findings facilitate focused testing of the CASK gene and interpreting sequence variants identified by next-generation sequencing in cases with a phenotype resembling either of the three groups.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-015-0256-3) contains supplementary material, which is available to authorized users.

Parental mosaicism of a novel PMP22 mutation with a minimal neuropathic phenotype

Genetic germinal and somatic mosaicisms of dominant Charcot-Marie-Tooth disease (CMT) mutations are rarely reported and/or recognized. We describe a novel heterozygous p.Trp39Cys missense mutation in the extracellular domain of the peripheral myelin protein 22 (PMP22) associated with an early-onset demyelinating CMT type 1 E (CMT1E) in two siblings born from asymptomatic non-consanguineous parents. The 29-year-old mother, harboring approximately 20% of the mutant PMP22 allele in blood, had minor signs of distal polyneuropathy (pes cavus, decreased ankle jerk reflexes and vibration sense in legs) and slight reduction of sural nerve action potentials (SNAPs). Authors suggest that mutations of CMT-related genes which originate in post-zygotic stages may be associated with mild phenotypes of peripheral neuropathy.

Mitotic instability in resynthesized and natural polyploids of the genus Arabidopsis (Brassicaceae)

Allopolyploids contain complete sets of chromosomes from two or more different progenitor species. Because allopolyploid hybridization can lead to speciation, allopolyploidy is an important mechanism in evolution. Meiotic instability in early-generation allopolyploids contributes to high lethality, but less is known about mitotic fidelity in allopolyploids. We compared mitotic stability in resynthesized Arabidopsis suecica-like neoallopolyploids with that in 13 natural lines of A. suecica (2n = 4x = 26). We used fluorescent in situ hybridization to distinguish the chromosomal contribution of each progenitor, A. thaliana (2n = 2x =10) and A. arenosa (2n = 4x = 32). Surprisingly, cells of the paternal parent A. arenosa had substantial aneuploidy, while cells of the maternal parent A. thaliana were more stable. Both natural and resynthesized allopolyploids had low to intermediate levels of aneuploidy. Our data suggest that polyploidy in Arabidopsis is correlated with aneuploidy, but varies in frequency by species. The chromosomal composition in aneuploid cells within individuals was variable, suggesting somatic mosaicisms of cell lineages, rather than the formation of distinct, stable cytotypes. Our results suggest that somatic aneuploidy can be tolerated in Arabidopsis polyploids, but there is no evidence that this type of aneuploidy leads to stable novel cytotypes.

Somatic and germline mosaicisms in Severe Myoclonic Epilepsy of Infancy

Severe Myoclonic Epilepsy in Infancy (SMEI) is an intractable epileptic syndrome with onset in the first year of life and is commonly caused by de novo mutations in the SCN1A gene, encoding the α1-subunit of the neuronal voltage-gated sodium channel. We report two unrelated families in which probands were affected by SMEI and their parents showed a single febrile seizure during early childhood or no neurological symptoms. Semiquantitative analysis of SCN1A mutations allowed the detection of a somatic and germline mosaicism in one of the parents. The study provides the first example of parental mosaicisms in SMEI and opens a new insight into the phenotypic variability and complex inheritance of this condition. The identification of germline mosaicisms has important consequences in genetic counseling of SMEI when SCN1A mutations appear to occur de novo with standard screening methods.

Androgen Insensitivity Syndrome: Somatic Mosaicism of the Androgen Receptor in Seven Families and Consequences for Sex Assignment and Genetic Counseling

Androgen insensitivity syndrome (AIS) is caused by numerous mutations of the androgen receptor (AR) gene. The phenotype may range from partial AIS (PAIS) with ambiguous genitalia to complete AIS (CAIS) with female genitalia. In 70% of the cases, AR mutations are transmitted in an X-linked recessive manner through the carrier mothers, but in 30%, the mutations arise de novo. When de novo mutations occur after the zygotic stage, they result in somatic mosaicisms, which are an important consideration for both virilization in later life-because both mutant and wild-type receptors are expressed-and genetic counseling. We report here six patients with AIS due to somatic mutations of the AR and one mother with somatic mosaicism who transmitted the mutation twice. Of the four patients with PAIS, three presented spontaneous or induced virilization at birth or puberty. These cases underline the crucial role of the remnant wild-type AR for virilization because the same mutations, when they are inherited, lead to CAIS. We also report two novel mutations of the AR, with somatic mosaicism, detected in patients with CAIS. Thus, the remnant wild-type receptor does not always lead to virilization. In one of these patients, a high ratio of wild-type to mutant AR expression was found in the gonads and genital skin fibroblasts. Although no prenatal virilization occurred, the possibility of virilization at puberty could not be excluded, and early gonadectomy was performed. A seventh patient had a CAIS with a novel germline AR mutation. The mutation was inherited from the mother, in whom mosaicism was detected in blood and who transmitted the mutation to a second, XX, offspring. The detection of somatic AR mutations is particularly important for the clinical management and genetic counseling of patients with AIS. Before definite sex assignment, a testosterone treatment trial should be performed in all patients with PAIS, but it becomes crucial when an AR mosaicism has been detected. In patients with CAIS or severe PAIS raised as female, there is no consensus about when (early childhood or puberty) gonadectomy should be performed. When somatic AR mutations are detected, however, gonadectomy should be performed earlier because of the risk of virilization during puberty. When a germline de novo mutation is identified in the index case, the risk of transmission to a second child due to a possible germ cell mosaicism in the mother cannot be excluded. However, given the high number of AR de novo mutations and the rarity of such reports, this risk appears to be very low.

Exclusion of mosaicism in Spanish haemophilia A families with inversion of intron 22

Inversion of intron 22, the most frequent mutation event in haemophilia A (HA), was tested in our HA families to diagnose the females at risk of being carriers, to trace the origin of the mutation and to investigate the presence of germinal or somatic mosaicism. A total of 166 females belonging to 54 families with inversion, were analysed. All but one of the mothers tested were carriers and the inversion originated almost exclusively in male germ cells. Somatic or germline mosaicisms were excluded in 53 of these women and in 20 grandfathers, suggesting that such mosaicisms may be a rare event in families with inversion of intron 22.