Trisomy 8 mosaicism: selective growth advantage of normal cells vs. growth disadvantage of trisomy 8 cells

Laryngotracheomalacia in a Patient with Mosaic Trisomy 8

Mosaic trisomy 8 is a condition characterized by a great phenotypic and cytogenetic variability whose incidence ranges around 1 in 25,000 to 50,000 live births. Here, we report a mosaic trisomy 8 patient presenting laryngotracheomalacia, an uncommon finding, analyzing its possible role over morbidity, and mortality. The patient was a boy who, after birth, had tachypnea and paleness. He presented periods of respiratory dysfunction with need of ventilatory support. Respiratory syncytial virus test was positive. Naso fibrobronchoscopy showed moderate laryngotracheomalacia. He also had recurrent episodes of pneumonia and difficulty in withdrawing continuous positive airway pressure. The patient also presented leucoma, abnormal and low-set ears, pectus excavatum, clenched fists with overlapping fingers, cryptorchidism, clubfeet, and deep longitudinal plantar creases. G-bands by Trypsin using giemsa (GTG-banding) karyotype from a peripheral blood sample revealed a mosaic trisomy 8: mos 47,XY, + 8[15]/46,XY[7]. At 4 months, the patient developed respiratory failure, and a chest computed tomography scan showed areas of atelectasis and gross fibroatelectatic striae. He ended up presenting clinical worsening and died at 4 months and 8 days. In our literature review, we found some reports describing patients with mosaic trisomy 8 and laryngotracheomalacia. However, we cannot rule out the possibility that this association could be casual, since laryngotracheomalacia is a relatively common finding in children. Therefore, more studies are still necessary to understand the possible relation between both conditions and the role of laryngotracheomalacia over morbidity and prognosis of mosaic trisomy 8 patients.

Prenatal diagnosis of trisomy 8 mosaicism, initially identified by cffDNA screening

BACKGROUND

So called cell-free fetal DNA (cffDNA) in the maternal plasma, which is derived from placenta, is widely used to screen fetal aneuploidies, including trisomy 21, 18, 13 and sex chromosomes. Here we reported a case of trisomy 8 mosaicism (T8M), which was initially identified via cffDNA screening in noninvasive prenatal testing (NIPT).

METHODS

A 35-year-old woman received cffDNA screening at 17th week of gestation. Amniocentesis was performed subsequently, and karyotyping, single-nucleotide polymorphism array (SNP-array) and BACs-on-Beads™ (BoBs™) were used to determine fetal chromosome content. Interphase fluorescence in situ hybridization (FISH) was applied to determine the copy number of chromosome 8.

RESULTS

An enhanced risk for fetal trisomy 8 was identified by cffDNA screening in the studied pregnant woman. After amniocentesis trisomy 8 was found in 1 of 73 metaphases. SNP-array on DNA derived from cultured amniocytes and neonatal cord blood cells suggested the presence of T8M. Interphase FISH on native neonatal cord blood cells confirmed T8M with a percentage of 10%. The Bobs™ fluorescence data also suggested that 8q23-8q24 was amplified.

CONCLUSIONS

The current study shows that NIPT is suited to provide hints on rare autosomal trisomies, which have to be further validated and confirmed by other approaches.

Trisomy 8 mosaicism in the placenta: A Danish cohort study of 37 cases and a literature review

OBJECTIVE

To evaluate the risk of fetal involvement when trisomy 8 mosaicism (T8M) is detected in chorionic villus samples (CVS).

METHODS

A retrospective descriptive study of registered pregnancies in Denmark with T8M in CVS identified through a database search and a review of published cases of T8M found through a systematic literature search and inclusion of cross references. Pregnancies with T8M in CVS and no additional numerical chromosomal aberrations were included.

RESULTS

A total of 37 Danish cases and 60 published cases were included. T8M detected in a CVS was associated with fetal involvement in 18 out of 97 pregnancies (18.6% [95%CI: 11.4-27.7]). Eight out of 70 (11.4% [95%CI: 5.1-21.3]) interpreted prenatally to be confined placental mosaicism (CPM) were subsequently found to be true fetal mosaicisms (TFM).

CONCLUSION

T8M detected in CVS poses a significant risk of fetal involvement, and examination of amniotic fluid (AF) and/or fetal tissue should be offered. However, a normal result of AF still has a considerable residual risk of fetal involvement. Genetic counselling at an early gestational age is essential, and follow-up ultrasonography should be performed to predict fetal involvement if possible.

Prenatal diagnosis of mosaic trisomy 8 by amniocentesis in a fetus with ventriculomegaly and dysgenesis of the corpus callosum

OBJECTIVE

We present prenatal diagnosis of mosaic trisomy 8 by amniocentesis in a fetus with central nervous system abnormalities.

CASE REPORT

A 39-year-old woman was found to have fetal bilateral ventriculomegaly and enlargement of the third ventricle on prenatal ultrasound at 32 weeks of gestation. Fetal magnetic resonance imaging examination confirmed bilateral ventriculomegaly and dysgenesis of the corpus callosum. Amniocentesis was performed subsequently. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniotic cells revealed trisomy 8 mosaicism with a result of arr [GRCh37] (8) × 3[0.19], (X,Y) × 1. Conventional cytogenetic analysis on cultured amniocytes showed that among 108 cells in 12 colonies of three cultures, only one cell was abnormal with trisomy 8, trisomy 9 and monosomy 13, while the rest 107 cells had a normal karyotype. Repeat amniocentesis and cord blood sampling revealed a result of arr 8p23.3q24.3 (191,530-146,280,020) × 2.3 with a log₂ ratio of 0.2 compatible with 20-30% mosaicism for trisomy 8 on the uncultured amniocytes, and a result of arr 8p23.3q24.3 (191,530-146,280,020) × 2.1 with a log₂ ratio of 0.08 compatible with <10% mosaicism for trisomy 8 on the cord blood lymphocytes. Polymorphic DNA marker analysis excluded uniparental disomy 8. A malformed 2440-g dead fetus was delivered at 34 weeks of gestation with facial dysmorphism.

CONCLUSION

Cytogenetic discrepancy can occur between cultured and uncultured amniocytes in mosaic trisomy 8 at amniocentesis. aCGH analysis on uncultured amniocytes is useful for confirmation of mosaic trisomy 8 at amniocentesis. Fetuses with low-level mosaicism for trisomy 8 may prenatally present ventriculomegaly and dysgenesis of the corpus callosum.

Prenatal detection of trisomy 8 mosaicism: Pregnancy outcome and follow up of a series of 17 consecutive cases

OBJECTIVE

To study the outcome of a series of individuals with prenatal detection of trisomy 8 mosaicism by chorionic villus sampling (CVS) and/or amniocentesis.

STUDY DESIGN

The databases of two Italian genetics units were reviewed to identify all consultations requested during pregnancy because of trisomy 8 mosaicism. To evaluate the pregnancy outcome, the regional registry of congenital malformations (including terminations of pregnancies) was consulted; additional follow-up data were collected by a telephone interview. The following outcomes were analysed: delivery, pre- and post-natal growth, psychomotor development, major malformations, other diseases/complications.

RESULTS

A total of 17 consecutive cases of trisomy 8 mosaicism were identified. Fourteen cases were first detected among women undergoing prenatal diagnosis by CVS; the remaining ones were identified among women who underwent amniocentesis. In most cases diagnosed by CVS, the chromosomal anomaly was only detected in long-term cell cultures (10/14) and was not confirmed by amniocentesis (11/13). There were two terminations of pregnancy and 15 live births; no major birth defects were observed among live born infants and only a case with prenatal and postnatal growth retardation was observed (mean age at follow-up interview was 5.9 years).

CONCLUSION

Our data showed an overall positive prognosis for cases with an apparent confined placental mosaicism and those with low-level mosaicism in amniotic fluid if no congenital anomalies were detected by foetal ultrasound examinations. However, larger studies are warranted to better define the associated risk of neurodevelopmental anomalies.

Search and insights into novel genetic alterations leading to classical and atypical Werner syndrome

Segmental progeroid syndromes are a group of disorders with multiple features resembling accelerated aging. Adult-onset Werner syndrome (WS) and childhood-onset Hutchinson-Gilford progeria syndrome are the best known examples. The discovery of genes responsible for such syndromes has facilitated our understanding of the basic mechanisms of aging as well as the pathogenesis of other common, age-related diseases. Our International Registry of Werner Syndrome accesses progeroid pedigrees from all over the world, including those for whom we have ruled out a mutation at the WRN locus. Cases without WRN mutations are operationally categorized as 'atypical WS' (AWS). In 2003, we identified LMNA mutations among a subset of AWS cases using a candidate gene approach. As of 2013, the Registry has 142 WS patients with WRN mutations, 11 AWS patients with LMNA mutations, and 49 AWS patients that have neither WRN nor LMNA mutations. Efforts are underway to identify the responsible genes for AWS with unknown genetic causes. While WS and AWS are rare disorders, the causative genes have been shown to have much wider implications for cancer, cardiovascular disease and the biology of aging. Remarkably, centenarian studies revealed WRN and LMNA polymorphic variants among those who have escaped various geriatric disorders.