Recurrence of lethal osteogenesis imperfecta due to parental mosaicism for a mutation in the COL1A2 gene of type I collagen. The mosaic parent exhibits phenotypic features of a mild form of the disease.

We have determined that a man, ascertained because he fathered a child with lethal osteogenesis imperfecta (OI) with each of two partners, is mosaic in both his germline and somatic tissues for a mutation in the COL1A2 gene which encodes the pro alpha 2(I) chain of type I procollagen. His dermal fibroblasts were previously shown to synthesize a population of cysteine-containing alpha 2(I) chains that were posttranslationally overmodified. DNA sequence analysis of COL1A2 cDNAs demonstrated that the cysteine-containing chain resulted from a point mutation (G to T) in the first position of the codon for the glycine at residue 472 of the triple helical domain. Genomic DNA from the one available affected infant contained the mutant and normal COL1A2 alleles in equal proportion. Examination of DNA from several tissues of the father showed that the mutant allele was present in approximately 40% of his sperm, 80% of his lymphocytes, and nearly 100% of his dermal fibroblasts. Despite the high level of mosaicism detected in somatic tissues, the only phenotypic manifestation of OI in the proband was that he was shorter than his unaffected male relatives and had mild dentinogenesis imperfecta. Thermal stability of type I collagen molecules containing the substitution was decreased, but to a lesser extent than for a nonlethal cysteine for glycine substitution at residue 259 of alpha 2(I), indicating that this measure of molecular stability may be of limited use in explaining the pathogenesis of osteogenesis imperfecta.     

Cytogentic studies of a patient with mosaicism of isochromosome 13q and a dicentric (Y; 13) translocation showing differential centromeric activity

A case is presened in which both an isochromosome and a dicentric translocation with differential centromere activity are found in one individual. Three karyotypes are present: 46, XY, -13, isochromosome 13q is found in 23% of cells in blood and 5% in skin. The dicentric (Y;13), + i(13q)/45,X, -13, + psu dic(13)t(13;Y)/45,X, -13, + psu dic(Y)t(Y;13). The isochromosome in all of the remaining cells displays differential centromeric activity; the ratio of cells with the acitve 13 centromere to the acstive Y centromere is about 3.5:1.
The formation of the isochromosome 13q was a de novo gametic event. The translocation producing the dicentric occurred after fertilization with the breakpoints at band Yq12 and the juxta-centromeric region of the isochromosome 13. The finding of differential centromeric activity in this chromosome indicates that centromere inactivation is not always permanent in a dicentric translocation.     

Tyrosinaemia type I—de novo mutation in liver tissue suppressing an inborn splicing defect

Many patients with tyrosinaemia type 1 have a mosaic pattern of fumarylacetoacetase (FAH) immunopositive or immunonegative nodules in liver tissue. This phenomenon has been explained by a spontaneous reversion of the mutation in one allele to a normal genotype, but only a few nodules have been examined. We now report on a Norwegian patient, compound heterozygous for the mutations IVS12g⁺⁵a and G¹⁰⁰⁹A, with liver mosaicism, but with an immunopositive nodule in which both primary mutations were intact. In the immunopositive hepatocytes of this nodule, genetic analyses showed a new mutation, C¹⁰⁶¹A, 6 bp upstream of the primary mutation IVS12g⁺⁵a in the FAH gene. The splicing defect caused by the primary mutation is most likely suppressed by the new mutation due to improvement of the splicing site. In the same liver we demonstrate another nodule of regenerating immunopositive tissue due to reversion of one of the primary mutations to a normal genotype. Together with the original cells this makes a triple mosaicism of hepatocytes with one, two or three point mutations in the FAH gene.     

Could PGT-A pick up true abnormalities that have clinical relevance? Retrospective analysis of 1043 embryos

ObjectiveTo determine whether preimplantation genetic testing for aneuploidy (PGT-A) could pick up true abnormalities that have clinical relevance.Materials and methodsThis was a retrospective cohort study of patients who underwent in vitro fertilization with PGT-A from 2015 to 2017. We evaluated the associations of aneuploidy and mosaicism with maternal age, the chromosome abnormalities present in individual chromosomes, and the effect of embryo sex on the proportion of each type of error in the four chromosomes most frequently affected.Result(s)A total of 1043 embryos from 255 patients (mean maternal age = 39 ± 4 years) were included in the initial analysis. Of these, 36% (377/1043) were euploid, 47% (487/1043) were aneuploid, 13% (140/1043) contained mosaicism, and 4% (39/1043) gave no result. We excluded the 39 embryos with no result; thus, 1004 embryos were included in the analysis. Increased aneuploidy was associated with increased maternal age, but the rate of embryo mosaicism was not. A combined analysis of aneuploidy with noncomplex abnormalities and mosaicism showed that chromosomes 22, 21, 16, and 15 were the most frequently involved. Chromosome 22 showed the highest proportion of mosaicism and chromosome 15 showed the highest proportion of aneuploidy. When we included embryo sex in the analysis, embryo sex was associated with these chromosome errors in the most susceptible chromosome, 22.Conclusion(s)PGT-A showed that chromosomes 22, 21, 16, and 15 were the most frequently involved among common chromosome abnormalities, comparable with those of published data analyzed from spontaneous abortion. This result suggested that PGT-A could pick up abnormalities that have clinical relevance to spontaneous abortion. Moreover, we identified a role of embryo sex in these chromosomal errors on chromosome 22.     

Cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes in mosaic double trisomy involving trisomy 7 and trisomy 20 (48,XY,+7,+20) at amniocentesis

ObjectiveWe present mosaic double trisomy involving trisomy 7 and trisomy 20 at amniocentesis in a pregnancy with a favorable outcome.Case reportA 41-year-old woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a result of 48,XY,+7,+20[6]/46,XY[26] in cultured amniocytes. At 19 weeks of gestation, repeat amniocentesis was performed, which revealed a result of 48,XY,+7,+20[4]/46,XY[21] in cultured amniocytes. Simultaneous molecular cytogenetic analyses on uncultured amniocytes at repeat amniocentesis revealed no genomic imbalance in array comparative genomic hybridization (aCGH) analysis, no trisomy 7 and no trisomy 20 signals in 114/114 cells in interphase fluorescence in situ hybridization (FISH) analysis, and no uniparental disomy (UPD) 7 and no UPD 20 in quantitative fluorescent polymerase chain reaction (QF-PCR) analysis. Interphase FISH analysis on cultured amniocytes revealed double trisomy of trisomy 7 and trisomy 20 in 5/105 cells (4.7%) compared with 0/100 cells (0%) in the normal control. Prenatal ultrasound findings were unremarkable. The parental karyotypes were normal. The woman decided to continue the pregnancy, and a healthy 2880-g phenotypically normal male baby was delivered at 34 weeks of gestation without any structural abnormality. The cord blood had a normal karyotype. Interphase FISH analysis of the urinary cells revealed no trisomy 7 and no trisomy 20 signals in 51/51 urinary cells.ConclusionCytogenetic discrepancy between cultured amniocytes and uncultured amniocytes can occur in mosaicism for double trisomy involving trisomy 7 and trisomy 20 at amniocentesis. Molecular cytogenetic analyses such as aCGH, FISH and QF-PCR on uncultured amniocytes are useful for rapid distinguishing true mosaicism from pseudomosaicism under such a circumstance.     

一例 TSC2基因嵌合变异致结节性硬化症患者的遗传学分析

目的:对1个结节性硬化症(tuberous sclerosis complex, TSC)家系进行 TSC1和 TSC2基因变异分析,明确其可能的致病原因。 方法:采集患者及其父母的外周血样,提取基因组DNA,应用靶向二代测序联合Sanger测序进行患者及其父母 TSC1和...     

Prenatal diagnosis of trisomy 18 as true mosaicism by three-dimensional ultrasonography: a case report

Trisomy of chromosome 18 is the second most common autosomal trisomy, occurring in approximately 1:7,000 live births. Its prenatal diagnosis through abnormal findings in ultrasound with later analysis of fetal karyotype is important for a definition of the prognosis and counseling of the patients. We describe a case of trisomy 18 as true mosaicism diagnosed through amniocentesis in the second trimester of pregnancy, associated to the presence of multiple fetal phenotypic alterations. We focus on the importance of fetal morphological study through three-dimensional ultrasonography, which was highly important for clearly showing the fetus’ structural alterations, helping parents to understand better the pathology and allowing them to reason about the continuity of the gestation.     

性染色体相嵌型胎儿的成纤维细胞体外生长稳定性的观察

性染色体相嵌型胎儿的成纤维细胞体外生长稳定性的观察内蒙古医学院第一附属医院（０１００５９）乔惠珍，周淑琴，施征洋ＯｂｓｅｒｖａｔｉｏｎｏｆｇｒｏｗｔｈｓｔａｂｉｌｉｔｙｏｆｆｉｂｒｏｂｌａｓｔｓｏｆｉｎｆａｎｔｓｗｉｔｈＳｅｘｃｈｒｏｍｏｓｏｍｅｍｏ...     

Advances in laboratory evaluation of turner syndrome and its variants : Beyond cytogenetics studies

Turner syndrome is a clinically defined phenotype that is characterized by partial or complete X chromosome monosomy. A host of cytogenetic aberrations and mosaicism have been associated with this syndrome. Some individuals, Turner syndrome variants, have cytogenetic findings consistent with Turner syndrome, but exhibit atypical clinical phenotypes. Recently, several molecular tests have been presented to allow for the refined clinical study of Turner syndrome and its variants.