Multiple independent second-site mutations in two siblings with somatic mosaicism for Wiskott-Aldrich syndrome

Wiskott–Aldrich syndrome (WAS) is an X-linked primary immunodeficiency disorder associated with microthrombocytopenia, eczema, autoimmunity and predisposition to malignant lymphoma. Although rare, few cases of somatic mosaicism have been published in WAS patients to date. We here report on two Ukrainian siblings who were referred to us at the age of 3 and 4 years, respectively. Both patients suffered from severe WAS caused by a nonsense mutation in exon 1 of the WAS gene. In both siblings, flow cytometric analysis revealed the presence of Wiskott–Aldrich syndrome protein (WASp)-positive and WASp-negative cell populations among T and B lymphocytes as well as natural killer (NK) cells. In contrast to previously described cases of revertant mosaicism in WAS, molecular analyses in both children showed that the WASp-positive T cells, B cells, and NK cells carried multiple different second-site mutations, resulting in different missense mutations. To our knowledge, this is the first report describing somatic mosaicism in WAS patients caused by several independent second-site mutations in the WAS gene.     

A comparative analysis of RAS variants in patients with disorders of somatic mosaicism

PurposeRAS genes (HRAS, KRAS, and NRAS) are commonly found to be mutated in cancers, and activating RAS variants are also found in disorders of somatic mosaicism (DoSM). A survey of the mutational spectrum of RAS variants in DoSM has not been performed.MethodsA total of 938 individuals with suspected DoSM underwent high-sensitivity clinical next-generation sequencing?based testing. We investigated the mutational spectrum and genotype?phenotype associations of mosaic RAS variants.ResultsIn this article, we present a series of individuals with DoSM with RAS variants. Classic hotspots, including Gly12, Gly13, and Gln61 constituted the majority of RAS variants observed in DoSM. Furthermore, we present 12 individuals with HRAS and KRAS in-frame duplication/insertion (dup/ins) variants in the switch II domain. Among the 18.3% individuals with RAS in-frame dup/ins variants, clinical findings were mainly associated with vascular malformations. Hotspots were associated with a broad phenotypic spectrum, including vascular tumors, vascular malformations, nevoid proliferations, segmental overgrowth, digital anomalies, and combinations of these. The median age at testing was higher and the variant allelic fraction was lower in individuals with in-frame dup/ins variants than those in individuals with mosaic RAS hotspots.ConclusionOur work provides insight into the allelic and clinical heterogeneity of mosaic RAS variants in nonmalignant conditions.     

Autosomal dominant polycystic kidney disease caused by somatic and germline mosaicism

Autosomal dominant polycystic kidney disease (ADPKD) is a heterogeneous genetic disorder caused by loss of function mutations of PKD1 or PKD2 genes. Although PKD1 is highly polymorphic and the new mutation rate is relatively high, the role of mosaicism is incompletely defined. Herein, we describe the molecular analysis of ADPKD in a 19‐year‐old female proband and her father. The proband had a PKD1 truncation mutation c.10745dupC (p.Val3584ArgfsX43), which was absent in paternal peripheral blood lymphocytes (PBL). However, very low quantities of this mutation were detected in the father's sperm DNA, but not in DNA from his buccal cells or urine sediment. Next generation sequencing (NGS) analysis determined the level of this mutation in the father's PBL, buccal cells and sperm to be ～3%, 4.5% and 10%, respectively, consistent with somatic and germline mosaicism. The PKD1 mutation in ～10% of her father's sperm indicates that it probably occurred early in embryogenesis. In ADPKD cases where a de novo mutation is suspected because of negative PKD gene testing of PBL, additional evaluation with more sensitive methods (e.g. NGS) of the proband PBL and paternal sperm can enhance detection of mosaicism and facilitate genetic counseling.     

L1 retrotransposition occurs mainly in embryogenesis and creates somatic mosaicism

Long Interspersed Element 1 (L1) is a retrotransposon that comprises ∼17% of the human genome. Despite its abundance in mammalian genomes, relatively little is understood about L1 retrotransposition in vivo. To study the timing and tissue specificity of retrotransposition, we created transgenic mouse and rat models containing human or mouse L1 elements controlled by their endogenous promoters. Here, we demonstrate abundant L1 RNA in both germ cells and embryos. However, the integration events usually occur in embryogenesis rather than in germ cells and are not heritable. We further demonstrate L1 RNA in preimplantation embryos lacking the L1 transgene and L1 somatic retrotransposition events in blastocysts and adults lacking the transgene. Together, these data indicate that L1 RNA transcribed in male or female germ cells can be carried over through fertilization and integrate during embryogenesis, an interesting example of heritability of RNA independent of its encoding DNA. Thus, L1 creates somatic mosaicism during mammalian development, suggesting a role for L1 in carcinogenesis and other disease.     

Clinical characteristics and rate of dilatation in Turner syndrome patients treated for aortic dilatation

Turner syndrome is associated with an increased risk of aortic aneurysms and dissection. Recent 2017 clinical care guidelines recommend medical therapy to treat aortic dilatation, although whether this slows dilatation is unknown. We aimed to describe a pre‐guideline cohort of Turner syndrome patients with aortic dilatation, the rate of dilatation following diagnosis, and post therapy dilatation rates. We conducted a retrospective review of Turner syndrome patients with a dilated aortic root or ascending aorta by current definitions. In total, 40 patients were included with 22 treated patients. Most patients had 45,X karyotype, were white, non‐Hispanic, and received both growth hormone and estrogen. Except for hypertension, there were no differences in risk factors among treated and untreated groups. Bicuspid aortic valve was very common. Treatment group patients had significantly more dilated ascending aortas by absolute measurements and aortic size index. In an adjusted model, there was minimal change in aortic measures over time and this was not associated with medication use. In conclusion, in this cohort, Turner syndrome patients with aortic dilatation were more likely to be treated if they had hypertension and if they met multiple dilatation criteria. Further study is needed to establish medical therapy efficacy on dilatation progression.     

High frequency of tissue-specific mosaicism in Turner syndrome patients

Interphase fluorescent studies of X chromosome aneuploidy in cultured and uncultured blood lymphocytes and oral mucosa epithelial cells using X centromere-specific DNA probe in addition to standard karyotype analysis were performed in 50 females with a clinical suspicion of Turner syndrome. All the patients were previously screened for the presence of 'hidden' Y chromosome mosaicism, using the primers DYZ3 and DYZ. The use of fluorescence in situ hybridization (FISH) analysis of interphase nuclei of tissues from different germ layers (lymphocytes from mesoderm and buccal epithelial cells from ectoderm) improves the accuracy of detection of low-level mosaicism. FISH studies on interphase nuclei revealed that 29% of patients with a pure form of monosomy X detected by metaphase analysis are, in fact, mosaics. The level of cells with the normal chromosomal constitution in lymphocytes of these cases as a rule was low, ranging from 3 to 18%, with an average of 7%. Two false-positive cases and one false-negative case of X monosomy mosaicism determined by standard cytogenetic approach were detected using FISH analysis. The majority of patients (92%) with mosaic form of Turner syndrome have considerable tissue-specific differences in levels of X aneuploidy. Our data indicate that in cases when mosaic aneuploidy with low-level frequency is questionable (approximately 10% and lower), the results of standard metaphase analysis should be supplemented with additional FISH studies of interphase nuclei. Tissue-specific differences in contents of different cell lines in the same patients point to the necessity of studying more than one tissue from each patient.     

Morphologic variants in parents of children with malformation syndromes: are they indicators of somatic mosaicism?

The ostensibly normal parents of 27 probands with recessive or sporadic multiple malformation syndromes were reexamined. By means of careful investigations and anthropometric measurements in nine of them, morphologic variants were found that were compatible with the syndromes and were also observed in the proband. Although other factors should also be considered, the findings may be explained by germline and somatic mosaicism in the parents.     

Parental gonadal but not somatic mosaicism leading to de novo NFIX variants shared by two brothers with Malan syndrome

The importance of gonadal mosaicism in families with apparently de novo mutations is being increasingly recognized. We report on two affected brothers initially suggestive of X‐linked or autosomal recessive inheritance. Malan syndrome due to shared NFIX variants was diagnosed in the brothers using exome sequencing. The boys shared the same paternal but not maternal haplotype around NFIX, and deep amplicon sequencing showed ~7% of the variant in paternal sperm but not in paternal blood and saliva. We performed review of previous cases of gonadal mosaicism, which suggests that the phenomenon is not uncommon. Gonadal mosaicism is often not accompanied by somatic mosaicism in tissues routinely used for testing, and if both types of mosaicism are present, the frequency of the variant in sperm is often higher than in somatic cells. In families with shared apparently de novo variants without evidence of parental somatic mosaicism, the transmitting parent may be determined through haplotyping of exome variants. Gonadal mosaicism has important consequences for recurrence risks and should be considered in genetic counseling in families with de novo variants.     

Identification of mosaicism in Prader-Willi syndrome using fluorescent in situ hybridization

We report on our findings of 4 patients with mosaicism for a deletion of chromosome 15, most commonly associated with Prader-Willi syndrome (PWS). We examined a series of typical and atypical PWS patients in order to identify cytogenetically undetected deletions, using fluorescence in situ hybridization. In 4 of the patients analyzed we detected a deletion in 14–60% of peripheral blood leukocytes, using four commercially available probes. Our results indicate that mosaicism may play a role in the etiology of some PWS cases. These findings may be especially useful in patients who display discrepancies between clinical phenotype and established diagnostic criteria. Methylation and microsatellite polymorphism analyses of 2 patients with low-level mosaicism failed to identify the deletion. We propose that fluorescence in situ hybridization is the most effective method for detecting somatic mosaicism, since a large number of cells can be individually examined for the presence or absence of a specific deletion. © 1996 Wiley-Liss, Inc.     

Somatic mosaicism in a mother of two children with Pitt–Hopkins syndrome

Steinbusch CVM, van Roozendaal KEP, Tserpelis D, Smeets EEJ, Kranenburg‐de Koning TJ, de Waal KH, Zweier C, Rauch A, Hennekam RCM, Blok MJ, Schrander‐Stumpel CTRM. Somatic mosaicism in a mother of two children with Pitt–Hopkins syndrome. Pitt–Hopkins syndrome (PTHS) is a neurodevelopmental disorder characterized by intellectual disability, unusual face and breathing abnormalities and can be caused by haploinsufficiency of TCF4. The majority of cases are sporadic. Somatic mosaicism was reported infrequently. We report on a proband with typical manifestations of PTHS and his younger brother with a less striking phenotype. In both, a heterozygous frameshift mutation (c.1901_1909delinsA, p.Ala634AspfsX67) was found in exon 19 of TCF4. The same mutation was found at low levels in DNA extracted from the mother's blood, urine and saliva. This report of familial recurrence with somatic mosaicism in a healthy mother has important consequences for genetic counseling. We suggest careful studies in parents of other patients with PTHS to determine the frequency of germline and somatic mosaicism for TCF4 mutations.     

Population Prevalence,Cancer Risk,and Mortality Risk of Turner Syndrome in South Korean Women Based on National Health Insurance Service Data

PurposeIn South Korea, investigations into Turner syndrome (TS) prevalence and TS-associated cancer and mortality are lacking. Accurate data were estimated from the National Health Insurance Service (NHIS) and the Rare Diseases Registry (RDR) records.Materials and MethodsData on patients with TS who were registered in the RDR between 2007 and 2017 were collected. To estimate TS-associated cancer and mortality risk, the data were compared with data of 1:3 age-matched controls.ResultsIn 2017, 2054 patients with TS were identified from a total population of 26186952 South Korean women; therefore, the prevalence was 7.84 per 100000 persons. TS prevalence across 10-year interval age groups were 11.82, 23.17, 18.37, 10.49, 4.09, and 0.38 for age under 10 years, teenagers, 20s, 30s, 40s, and older than 50, respectively (per 100000 persons). The cancer risk in patients with TS was higher than that of age-matched controls over 5.3 person-years [hazard ratio (HR)=1.82, 95% confidence interval (CI) 1.01–3.27, p=0.045]. Among different types of cancer, thyroid cancer risk in patients with TS was significantly higher than that of age-matched controls (HR=2.78, 95% CI 1.06–7.26, p=0.037). We also observed that TS-associated all-cause mortality risk was higher than that of age-matched controls (HR=3.36, 95% CI 1.59–7.10, p=0.002).ConclusionNational prevalence of TS was suggested, and an increased risk of TS-associated thyroid cancer and mortality were observed in this study.     

Trisomy 1 mosaicism only detected on a direct chromosome preparation in a neonate

A patient is described with trisomy 1 mosaicism which was discovered on 24-h culture of a neonatal blood sample, but was not detectable on subsequent 48- and 72-h cultures. This result complements other recent reports and has important implications for the detection of mosaicism in neonates.     

A series of 38 novel germline and somatic mutations of NIPBL in Cornelia de Lange syndrome

Cornelia de Lange syndrome is a multisystemic developmental disorder mainly related to de novo heterozygous NIPBL mutation. Recently, NIPBL somatic mosaicism has been highlighted through buccal cell DNA study in some patients with a negative molecular analysis on leukocyte DNA. Here, we present a series of 38 patients with a Cornelia de Lange syndrome related to a heterozygous NIPBL mutation identified by Sanger sequencing. The diagnosis was based on the following criteria: (i) intrauterine growth retardation and postnatal short stature, (ii) feeding difficulties and/or gastro‐oesophageal reflux, (iii) microcephaly, (iv) intellectual disability, and (v) characteristic facial features. We identified 37 novel NIPBL mutations including 34 in leukocytes and 3 in buccal cells only. All mutations shown to have arisen de novo when parent blood samples were available. The present series confirms the difficulty in predicting the phenotype according to the NIPBL mutation. Until now, somatic mosaicism has been observed for 20 cases which do not seem to be consistently associated with a milder phenotype. Besides, several reports support a postzygotic event for those cases. Considering these elements, we recommend a first‐line buccal cell DNA analysis in order to improve gene testing sensitivity in Cornelia de Lange syndrome and genetic counselling.     

The bicuspid aortic valve and its relation to aortic dilation

BACKGROUND

A bicuspid aortic valve (BAV) is a common congenital heart disease, which affects 1–2% of the population. However, the relationship between BAVs and aortic dilation has not been sufficiently elucidated.

METHODS

A total of 241 BAV patients who were referred to this hospital for cardiac surgey over a 4.75-year period were included in this study. In addition to the clinical characteristics of the included patients, the morphological features of the aortic valve and aorta, the length of the left main coronary artery, and the laboratory findings (the coagulation and hematological parameters as well as the total cholesterol concentration) were determined and compared with those of the tricuspid aortic valve (TAV) patients.

RESULTS

The BAV patients were younger than the TAV patients for a valve surgery in the last 3 months of the study period. The BAV patients were predominantly male. Most of the BAVs that were surgically treated were stenotic, regurgitant, or combined, and only 19 (7.88%) were normally functioning valves. According to echocardiography or operative records, 148 (78.31%) were type A, 31 (16.40%) were type B, and 10 (5.29%) were type C. The left main coronary artery was much shorter in the BAV patients than it was in the TAV patients. There was no significant difference between BAV and TAV patients in the total cholesterol concentrations; whereas differences were noted between patients receiving lipid-lowering therapy and those not receiving lipid-lowering therapy. The dimensions of the aortic root, sinotubular junction, and ascending aorta were beyond normal limits, while they were significantly smaller in the BAV patients than in the TAV patients. They were also much smaller in patients receiving statin therapy than those not receiving statin therapy in both groups. Moreover, the aortic dilation in the BAV group was found to be significantly associated with patient age.

CONCLUSIONS

The BAV patients developed aortic wall and aortic valve disorders at a younger age than the TAV patients and were predominantly male. Aortic dilation was observed in the aortic root, sinotubular junction, and ascending aortic segments in both the BAV and TAV patients undergoing surgical aortic valve replacement, although the BAV patients had a smaller degree of dilation than the TAV patients, and dilation was also significantly age-related in this group. The shorter left main coronary artery that the BAV patients possess may contribute to the progressive course of aortic dilation that these patients experience. Statin therapy did not affect the aortic annulus in either group, but did decrease the dimensions of the aortic root, sinotubular junction and ascending aorta. In general, statin therapy had a better effect on the aortas of the TAV patients than it did on those of the BAV patients.     

Segregation of the fragile X mutation from a male with a full mutation: Unusual somatic instability in the FMR-1 locus

Fragile X syndrome is associated with an unstable CGG-repeat in the FMR-1 gene. There are few reports of affected males transmitting the FMR-1 gene to offspring. We report on a family in which the propositus and his twin sister each had a full mutation with abnormal methylation. Their mother had an FMR-1 allele in the normal range and a large premutation, with normal methylation. The maternal grandmother had two normal FMR-1 alleles. The maternal grandfather had an unusual somatic FMR-1 pattern, with allele size ranging from premutation to full mutation. No allele was detectable by PCR analysis. Multiple Southern blot analyses identified a hybridization pattern that originated at a distinct premutation band and extended into the full mutation range. Methylation studies revealed a mosaic pattern with both unmethylated premutations and methylated full mutations. This individual declined formal evaluation but did not finish high school and has difficulty in reading and writing. The size of the premutation FMR-1 allele passed to his daughter is larger than his most prominent premutation allele. This is most likely due to gonadal mosaicism similar to that in his peripheral lymphocytes. Alternatively, this expansion event may have occurred during his daughter's early embryonic development and this large premutation allele is mitotically unstable. This pattern of FMR-1 alleles in a presumably mildly affected male is highly unusual. These findings are consistent with the absence of transmission of a full fragile X mutation through an expressing male. Studies of tissue specific FMR-1 allele expansion and FMR-1 protein expression on this individual should help to determine the correlation of the molecular findings with the phenotypic effects. © 1996 Wiley-Liss, Inc.