Prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome derived from 2q11.1-q12.1 associated with fetal bilateral radial dysplasia

ObjectiveWe present prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome (sSMC) derived from 2q11.1-q12.1 associated with fetal bilateral radial dysplasia.Case reportA 27-year-old woman underwent amniocentesis at 18 weeks of gestation because of club hands on fetal ultrasound. The internal organs of the fetus were normal. Amniocentesis revealed a karyotype of 47,XY,+mar [13]/46,XY [11]. The parental karyotypes were normal. Simultaneous array comparative genomic hybridization (aCGH) analysis of the DNA extracted from uncultured amniocytes revealed the result of arr 2q11.1q12.1 (95,529,039–102,825,556) × 3.0 [GRCh37 (hg19)]. The pregnancy was terminated at 20 weeks of gestation, and a malformed fetus was delivered with isolated bilateral radial dysplasia. The cord blood had a karyotype of 47,XY,+mar[24]/46,XY[16]. Polymorphic DNA marker analysis of the DNAs extracted from umbilical cord and parental bloods excluded uniparental disomy for chromosome 2. Metaphase fluorescence in situ hybridization analysis confirmed an sSMC derived from chromosome 2q11.1-q12.1 in cultured amniocytes.ConclusionHigh-level mosaicism for an sSMC derived from chromosome 2q11.1-q12.1 can be associated with fetal abnormalities.     

45,X/47,XY,+ 13 Mosaicism and Crohn's Disease

ABSTRACT. The unusual karyotype 4S,X/47,XY,+13 in an 8.5-year-old girl with the Turner phenotype is described. She displayed none of the phenotypic manifestations of trisomy 13. The patient suffered from Crohn's disease, which is known to be associated with the Turner syndrome. To our knowledge this is the first reported case of Crohn's disease in a patient with 45,X and Y chromosome mosaicism.     

Early diagnosis enabling precision medicine treatment in a young boy with PIK3R1-related overgrowth

Mosaic PIK3R1 variants have recently been demonstrated in patients with complex vascular malformations and overgrowth in a syndrome resembling PIK3CA-related overgrowth syndrome (PROS). The PIK3CA-inhibitor, alpelisib, seems to be a promising treatment option for PROS patients. We describe a young boy with overgrowth and a pathogenic mosaic variant in PIK3R1; c.1699A > G, p.(Lys567Glu). He was prenatally suspected of a syndrome on the presence of unusual transient fluctuating subcutaneous edemas and lymphedema of his left shoulder. The pathogenic variant, later found to be causative, was below detection threshold in whole-genome sequencing (WGS) analysis of amniotic fluid. Upon delivery a mosaic pathogenic PIK3R1 variant, was identified by whole-exome sequencing (WES) of a skin biopsy. With no proven treatment options available, and based on the theoretical disease mechanism, alpelisib therapy was initiated at nine months of age. In the first year of treatment growth normalized and the affected vascular and lymphatic tissue regressed. No side effects have been observed. This report underlines the importance of early variant detection in children suspected of having severe mosaic overgrowth, and proves that prenatal diagnosis is possible, enabling prompt treatment. Furthermore, it demonstrates the promising effects of alpelisib in this patient group.     

45,X/46,XY mosaicism and Oculo-Auriculo-Vertebral Spectrum following an IVF pregnancy: a report and a discussion of their interrelationships

The aetiology of Oculo-Auriculo-Vertebral Spectrum (OAVS) is unkown. We report a case following a prenatal diagnosis of 45,X/46,XY mosaicism in a pregnancy achieved by In-Vitro Fertilization (IVF) and describe evidence for the interrelationships of these phenomena and multiple births. This report extends the phenotypes associated with prenatally diagnosed 45,X/46,XY mosaicism and supports the association of OAVS and IVF.     

Imprinting center analysis in Prader-Willi and Angelman syndrome patients with typical and atypical phenotypes

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are genetic disorders caused by a deficiency of imprinted gene expression from the paternal or maternal chromosome 15, respectively. This deficiency is due to the deletion of the 15q11-q13 region, parental uniparental disomy of the chromosome 15, or imprinting defect (ID). Mutation of the UBE3A gene causes approximately 10% of AS cases. In this present study, we describe the molecular analysis and phenotypes of two PWS patients and four AS patients with ID. One of the PWS patients has a non-familial imprinting center (IC) deletion and displayed a severe phenotype with an atypical PWS appearance, hyperactivity and psychiatric vulnerability. The other PWS and AS patients did not present genetic abnormalities in the IC, suggesting an epimutation as the genetic cause. The methylation pattern of two AS patients showed a faint maternal band corresponding to a mosaic ID. One of these mosaic patients displayed a mild AS phenotype while the other displayed a PWS-like phenotype.     

Construction of a high-density and high-resolution human chromosome X array for comparative genomic hybridization analysis

The human chromosome X is closely associated with congenital disorders and mental retardation (MR), because it contains a significantly higher number of genes than estimated from the proportion in the human genome. We constructed a high-density and high-resolution human chromosome X array (X-tiling array) for comparative genomic hybridization (CGH). The array contains a total of 1,001 bacterial artificial chromosome (BACs) throughout chromosome X except pseudoautosomal regions and two BACs specific for Y. In four hybridizations using DNA samples from healthy males, the ratio of each spotted DNA was scattered between −3SD and 3SD, corresponding to a log₂ ratio of −0.35 and 0.35, respectively. Using DNA samples from patients with known congenital disorders, our X-tiling array was proven to discriminate one-copy losses and gains together with their physical sizes, and also to estimate the percentage of a mosaicism in a patient with mos 45,X[13]/46,X,r(X)[7]. Furthermore, array-CGH in a patient with atypical Schinzel-Giedion syndrome disclosed a 1.1-Mb duplication at Xq22.3 including a part of the IL1RAPL2 gene as a likely causative aberration. The results indicate our in-house X-tiling array to be useful for the identification of cryptic copy-number aberrations containing novel genes responsible for diseases such as congenital disorders and X-linked MR.     

Gait disturbance and lower limb pain in a patient with PIK3CA-related disorder

Post-zygotic activating mutations in PIK3CA and other genes encoding members of PI3K-AKT-mTOR pathway have been found in various overgrowth syndromes that have been grouped together as PIK3CA-related overgrowth spectrum (PROS). We report a female patient with gait disturbance, leg pain, isolated macrodactyly of the foot, and mild intellectual disability. Imaging of the lower limb showed a lipoblastoma of the right thigh. A mosaic gain-of-function mutation in the catalytic domain of PIK3CA (c.3140 A > G; p.His1047Arg) was detected in the adipose tissue and in skin cultured fibroblasts from the macrodactyly but not in blood. The leg pain and the severe walking disturbance improved slightly over time and serial MRI of the lower limbs suggested that the size of the lipoblastoma relative to the lower limb muscles or to the whole lower limb was unchanged as consequence of limb growth. This case report illustrates that pain and gait disturbance can be features of PROS and highlights the need of better knowledge about the natural history of the disease.     

Low-level mosaicism for trisomy 16 at amniocentesis in a pregnancy associated with intrauterine growth restriction and a favorable outcome

ObjectiveWe present low-level mosaicism for trisomy 16 at amniocentesis in a pregnancy associated with intrauterine growth restriction (IUGR) and a favorable outcome.Case reportA 31-year-old woman underwent amniocentesis at 24 weeks of gestation because of IUGR. Amniocentesis revealed a karyotype of 47,XX,+16 [3]/46,XX [22]. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed gene dosage increase in chromosome 16 consistent with 28% mosaicism for trisomy 16. Uniparental disomy (UPD) 7 and UPD 11 were excluded. She underwent repeat amniocentesis at 27 weeks of gestation. Repeat amniocentesis revealed a karyotype of 47,XX,+16 [1]/46,XX [24]. Simultaneous aCGH analysis on the DNA extracted from uncultured amniocytes revealed 25%–35% (log₂ ratio = 0.17–0.25) mosaicism for trisomy 16. Interphase fluorescence in situ hybridization (FISH) analysis detected trisomy 16 signals in 28/100 (28%) uncultured amniocytes. Polymorphic DNA marker analysis excluded UPD 16. Level II ultrasound revealed no fetal abnormalities except symmetric IUGR. The pregnancy was continued to 37 weeks of gestation, and a 2306-g phenotypically normal baby was delivered. The cord blood had a karyotype of 46, XX in 50/50 lymphocytes. The umbilical cord had a karyotype of 47,XX,+16 [14]/46,XX [36]. Interphase FISH analysis on buccal mucosal cells and urinary cells at age three days revealed trisomy 16 signals in 3.8% (4/106) buccal mucosal cells and 6.5% (7/107) urinary cells, compared with 1% in the normal control. Polymorphic DNA marker analysis on placenta confirmed trisomy 16 in the placenta and a maternal origin of the extra chromosome 16.ConclusionCytogenetic discrepancy between cultured amniocytes and uncultured amniocytes may present in mosaic trisomy 16 at amniocentesis. Low-level mosaicism for trisomy 16 at amniocentesis without maternal UPD 16 can be associated with a favorable outcome despite the presence of IUGR.     

一例散发1型神经纤维瘤病患者的NF1基因嵌合突变分析

目的 对1例散发1型神经纤维瘤病患者的NF1基因进行嵌合突变分析.方法 提取先证者外周血基因组RNA,PCR扩增NF1基因编码区序列并进行序列测定;找到突变后,基因组DNA途径证实突变,并对先证者儿子的NF1基因相应外显子也进行序列分析;针对NF1基因第51外显子已发现的突变,取先证者全血淋巴细胞、口腔上皮细胞和尿路上皮细胞基因组DNA进行PCR扩增,PCR产物T克隆及测序.结果 先证者的临床表现符合1型神经纤维瘤病.先证者外周血RNA途径检测出无义突变c.7911C＞T(p.Q2510X);基因组DNA途径证实患者外周血淋巴细胞、口腔上皮细胞和尿路上皮细胞中均有该突变,尿路上皮细胞中该突变测序信号较弱;在PCR产物的T克隆-测序中,来自先证者的血液、口腔上皮、尿液上皮细胞无义突变c.7911C＞T(p.Q2510X)突变体的重组菌分别占总数的42％、36％、12％.其儿子、正常对照不存在上述突变.结论 先证者在胚胎早期发生了NF1基因突变,使其体内部分细胞带有NF1基因突变,导致形成全身嵌合的1型神经纤维瘤病.     

Adults with a history of possible Dravet syndrome: an illustration of the importance of analysis of the SCN1A gene

Most patients with Dravet syndrome have de novo mutations in the neuronal voltage-gated sodium channel type 1 (SCN1A) gene. We report on two unrelated fathers with severe childhood epilepsy compatible with a possible diagnosis of Dravet syndrome, who both have a child with Dravet syndrome. Analysis of the SCN1A gene revealed a pathogenic mutation in both children. One father exhibited somatic mosaicism for the mutation detected in his son. A relatively favorable cognitive outcome in patients with Dravet syndrome patients may be explained by somatic mosaicism for the SCN1A mutation in brain tissue. A mild form of Dravet syndrome in adult patients is associated with a high recurrence risk and possibly a more severe epilepsy phenotype in their offspring.