Tetrasomy 18p: report of the molecular and clinical findings of 43 individuals

Understanding type and quality of relationships between individuals with chromosome 18 syndromes and their siblings

Siblings of individuals with disabilities hold a pivotal and sometimes unappreciated position in the lives of their brother or sister. We sought to understand the unique challenges and opportunities in relationships between children with chromosome 18 conditions and their siblings and to identify the ways to support this relationship. Participants were recruited through the lay advocacy organization, the Chromosome 18 Registry & Research Society. Fifty-seven siblings from 36 families participated, using an investigator designed instrument, were asked to agree or disagreed with statements from four content areas (information and knowledge about the syndrome, feelings about the sibling relationship, involvement with and caregiving for their sibling, and support and advocacy). Siblings reported that they know their sibling with a disability very well and reported a wide range of emotions regarding their sibling. There was a strong sense of pride in their brother/sister's abilities, and many participants reported attempts to help others understand their brother/sister. Many siblings reported a dislike for the common assumption that their affected sibling is a burden on the family. Most participants reported feeling some degree of responsibility for their affected sibling, but many also reported that they enjoy this role. Sixty-three parents from 36 families responded to the survey. Most parents felt their typically developing children enjoyed teaching new things to their affected child as well as being a good role model for them. Most parents also felt their typically developing child was comfortable telling others about their sibling's condition. Recommendations for interventions and future research are discussed.

Phenotypic and cytogenetic features of an Iranian child with tetrasomy 18p syndrome: A case report

BACKGROUND

Tetrasomy 18p is a rare chromosome abnormality disorder known to have considerable variability in clinical features and gathering data from different cases will help clinicians and researchers learn about its genotype-phenotype relationship and diagnosis.

CASE SUMMARY

Herein, we have reviewed the literature on phenotypic features of this disorder and described the phenotypic and cytogenetic features of a girl of early childhood with tetrasomy 18p for the first time from Iran. This patient showed a strong sense of smell (a unique feature not reported previously for this syndrome), had clenched hand, pes planus, forward head posture in walking and hirsutism (dysmorphic features less reported), and showed 10 clinical features that are generally observed in previously reported cases, including developmental delay/intellectual disability, triangular face, smooth philtrum, feeding difficulties, hypotonia, epicanthus, strabismus, history of constipation, growth retardation and foot anomalies. G-banding chromosome analysis from peripheral blood revealed an abnormal female karyotype with a small marker chromosome (47,XX, +mar), and oligo-array comparative genomic hybridization displayed a gain of 14Mb of the 18p arm containing 56 Online Mendelian Inheritance in Man (OMIM) genes in this patient. Overall, this patient seems to have mild phenotypes.

CONCLUSION

This Iranian tetrasomy 18p child displays a uniquely strong sense of smell, some less reported dysmorphic features and ten features generally reported.

Diagnostic workup in children with arthrogryposis: description of practices from a single reference centre, comparison with literature and suggestion of recommendations

INTRODUCTION

Arthrogryposis multiplex congenita (AMC) refers to a clinical presentation of congenital contractures involving two or more body areas. More than 400 distinct conditions may lead to AMC, making the aetiological diagnosis challenging. The objective of this work was to set up evidence-based recommendations for the diagnosis of AMC by taking advantage of both data from our nation-wide cohort of children with AMC and from the literature.

MATERIAL AND METHODS

We conducted a retrospective single-centre observational study. Patients had been evaluated at least once at a paediatric age in the AMC clinic of Grenoble University Hospital between 2007 and 2019. After gathering data about their diagnostic procedure, a literature review was performed for each paraclinical investigation to discuss their relevance.

RESULTS

One hundred and twenty-five patients were included, 43% had Amyoplasia, 27% had distal arthrogryposis and 30% had other forms. A definitive aetiological diagnosis was available for 66% of cases. We recommend a two-time diagnostic process: first, non-invasive investigations that aim at classifying patients into one of the three groups, and second, selected investigations targeting a subset of patients.

CONCLUSION

The aetiological management for patients with AMC remains arduous. This process will be facilitated by the increasing use of next-generation sequencing combined with detailed phenotyping. Invasive investigations should be avoided because of their limited yield.

Prenatal genetic diagnosis of tetrasomy 18p from maternal trisomy 18p: a case report

BACKGROUND

Tetrasomy 18p syndrome is a rare chromosomal disorder that is caused by the presence of isochromosome 18p. Most tetrasomy 18p cases are de novo cases and maternal origin of trisomy 18p is a rare condition. At present, only four cases of maternal origin have been reported in worldwide.This is the fifth case of tetrasomy 18p originating from maternal trisomy 18p. The mother of the fetus studied had no apparent disease phenotype.

CASE PRESENTATION

The current case report is to describe a fetus with confirmed 18p tetrasomy as detected by karyotyping and Single Nucleotide Polymorphism array (SNP array) analysis. However, the fetus showed normal phenotypic features that were observed using ultrasound scans. The mother and maternal grandfather were phenotypically normal and healthy; however, they were diagnosed with trisomy 18p, which was confirmed by conventional karyotyping and SNP array.

CONCLUSIONS

We report a case of 18p tetrasomy in a fetus whose mother and grandfather had 18p trisomy. The mother and grandfather were phenotypically normal. Our case report findings provide an important reference for the genetic counseling of trisomy 18p in the future.

Minimally invasive endoscopic fenestration of a spinal arachnoid cyst in a child with tetrasomy 18p: illustrative case

BACKGROUND

Spinal arachnoid cysts (SAC) are rare, especially in children. Patients can be asymptomatic or present symptoms of spinal cord compression. In this latter case, surgery is indicated to relieve the compression. Different surgical techniques have been described to treat these cysts, endoscopic or endoscopy-assisted fenestration being the least invasive. Tetrasomy 18p describes the condition in which two copies of the short arms of chromosome 18 are present. It is an extremely rare pathology with a variable phenotype, including 100% of cases cognitive impairment and developmental delay. Different central nervous system (CNS) abnormalities have been found in these patients.

OBSERVATIONS

The authors describe the case of a 3-year-old boy with a tetrasomy 18p and a wide spinal arachnoid cyst that received an endoscope-assisted treatment with a significantly improved motor outcome.

LESSONS

Tetrasomy 18p is an extremely rare pathology and different CNS abnormalities have been described in association with, but to date spinal arachnoid cyst has never been reported. These children typically show global hypotonia and cognitive impairment. The authors recommend a thorough neurological assessment with cranio-spinal magnetic resonance imaging to rule out any possible malformation that could be improved by surgery.

Partial tetrasomy 18 mosaicism: Pre and postnatal diagnosis of a unique pattern

OBJECTIVE

To present prenatal diagnosis and cytogenetic characterization of a unique pattern of partial tetrasomy 18 mosaicism.

CASE REPORT

A 34-year-old woman underwent amniocentesis at 25 weeks of gestation due to anomalies detected in obstetric ultrasound. It revealed a de novo supernumerary partial isochromosome 18 in 11 of 37 metaphases of cultured amniocytes. The karyotype was 47,XX,+idic(18) (q12.3)[11]/46,XX[26]. Elective cesarean section was performed at 33 weeks of gestational age due to anhydramnios. A female symmetric small for gestational age baby with dysmorphic features and an Apgar score of 9/10/10 was born. She had a good clinical outcome during hospitalization. Postnatal peripheral blood karyotype was normal. Interphase fluorescence in situ hybridization in a sample of the oral mucosa confirmed the prenatal diagnosis. At three months of corrected age she had a normal psychomotor development.

CONCLUSION

To the best of our knowledge, this is the first reported case of mosaic partial tetrasomy 18 including segments of the long arm. This newborn's relatively mild phenotype highlights the challenges of prenatal genetic counselling in mosaic cases with fetal anomalies.

Tetrasomy 18p Initially Misdiagnosed as Cerebral Palsy in an Adult Patient

Tetrasomy 18p is a rare genetic condition characterized by a supernumerary 18p isochromosome with two copies of the p arm of chromosome 18 causing patients to have an extra chromosome. Most cases are de novo; however, a few maternally inherited cases have been reported. The most commonly reported manifestations of this condition are developmental delay, cognitive impairments, muscle tone abnormalities, and dysmorphic facial features. This case details a new diagnosis of tetrasomy 18p in a 42-year-old adult who was initially diagnosed with cerebral palsy as a child. We compare the phenotypic traits of our patient with the ones reported in the literature.

Eye, Ocular Adnexa, and Facial Manifestations of Tetrasomy 18p

Tetrasomy 18p is often the result of an additional isochromosome for the short arm of chromosome 18. Although many organ systems are affected phenotypically, the ocular manifestations associated with tetrasomy 18p have not been well characterized in the literature. This case report presents the ocular and facial features associated with tetrasomy 18p in a 4-year-old Black girl, along with a review of clinical presentations previously reported in the literature. A systematic review of the literature in PubMed was conducted to summarize the reported eye, ocular adnexa, and distinctive facial features in individuals with confirmed tetrasomy 18p. Searching "Tetrasomy 18p" generated 65 article results, of which 28 articles had sufficient eye and facial descriptions. Including the patient in this report, 90 patients had confirmed tetrasomy 18p. The most common features noted in these 90 patients, with a roughly equal male-to-female ratio of impact (7:8), were as follows: microcephaly (57%), triangular facies (18%), anomalous palpebral fissures (31%), strabismus (48%), low-set ears (52%), hearing loss to some extent (16%), depressed or flat nasal bridge (18%), smooth philtrum (41%), thin upper lip (27%), and highly arched palate (21%). Additionally, many were noted to have feeding difficulties (28%), developmental delay (58%), and abnormal brain findings on imaging (20%). Muscle tone was abnormal in 23% of the patients. This report elucidates the reoccurring eye, ocular adnexa, and distinctive facial features associated with tetrasomy 18p. This knowledge may assist in timely diagnosis and encourage providers to use a multidisciplinary approach for the treatment of affected individuals. [J Pediatr Ophthalmol Strabismus. 2021;58(6):e44-e48.].

BACs-on-Beads Assay for the Prenatal Diagnosis of Microdeletion and Microduplication Syndromes

OBJECTIVE

To evaluate the clinical value of BACs-on-Beads (BoBs) assay in detection of microdeletion and microduplication syndromes.

METHODS

A total of 6,814 cases of amniotic fluid cells collected from January 2015 to July 2020 in our hospital were analyzed by chromosomal karyotyping and BoBs assay. Fluorescence in situ hybridization (FISH) or chromosomal microarray analysis (CMA) provided further validation for the cases of microdeletion and microduplication.

RESULTS

Thirty microdeletion and microduplication syndromes were identified by BoBs with an incidence of ~1/227, including 22q11.2 microduplication (0.044%, 3/6814), DiGeorge I syndrome (0.044%, 3/6814), 17p11.2 microduplication (0.015%, 1/6814), Smith-Magenis syndrome (0.015%, 1/6814), 17p11.2p11.3 microduplication (0.015%, 1/6814), Williams-Beuren syndrome (0.088%, 6/6814), 7q11.2 microduplication (0.029%, 2/6814), DiGeorge II syndrome (0.015%, 1/6814), 18p11.32p11.21 microduplication (0.015%, 1/6814), Wolf-Hirschhorn syndrome (0.029%, 2/6814), 4p16.3 microduplication (0.015%, 1/6814), Langer-Giedion syndrome (0.015%, 1/6814), Miller-Dieker syndrome (0.015%, 1/6814), Cri du Chat syndrome (0.015%, 1/6814), Xp22.31 microdeletion (0.059%, 4/6814), Prader-Willi syndrome (0.015%, 1/6814). High concordance was obtained between BoBs and FISH or CMA. However, only four cases were detected by chromosomal karyotyping.

CONCLUSION

BoBs assay can rapidly detect microdeletion and microduplication syndromes, which compensates the shortcomings of conventional chromosomal karyotyping and greatly improves the efficiency and accuracy of prenatal diagnosis.

Variable degree of mosaicism for tetrasomy 18p in phenotypically discordant monozygotic twins-Diagnostic implications

Background

Phenotypically discordant monozygotic twins (PDMZTs) offer a unique opportunity to study post‐zygotic genetic variation and provide insights into the linkage between genotype and phenotype. We report a comprehensive analysis of a pair of PDMZTs.

Methods

Dysmorphic features and delayed neuro‐motor development were observed in the proband, whereas her twin sister was phenotypically normal. Four tissues (blood, skin, hair follicles, and buccal mucosa) from both twins were studied using four complementary methods, including whole‐exome sequencing, karyotyping, array CGH, and SNP array.

Results

In the proband, tetrasomy 18p affecting all studied tissues except for blood was identified. Karyotyping of fibroblasts revealed isochromosome 18p [i(18p)] in all metaphases. The corresponding analysis of the phenotypically normal sister surprisingly revealed low‐level mosaicism (5.4%) for i(18p) in fibroblasts.

Conclusion

We emphasize that when mosaicism is suspected, multiple tissues should be studied and we highlight the usefulness of non‐invasive sampling of hair follicles and buccal mucosa as a convenient source of non‐mesoderm‐derived DNA, which complements the analysis of mesoderm using blood. Moreover, low‐level mosaic tetrasomy 18p is well tolerated and such low‐level mosaicism, readily detected by karyotyping, can be missed by other methods. Finally, mosaicism for low‐level tetrasomy 18p might be more common in the general population than it is currently recognized, due to detection limitations.

Genotype-phenotype correlation in 75 patients with small supernumerary marker chromosomes

Background

Small supernumerary marker chromosomes (sSMCs) are rare structural abnormalities in the population; however, they are frequently found in children or fetuses with hypoevolutism and infertile adults. sSMCs are usually observed first by karyotyping, and further analysis of their molecular origin is important in clinical practice. Next-generation sequencing (NGS) combined with Sanger sequencing helps to identify the chromosomal origins of sSMCs and correlate certain sSMCs with a specific clinical picture.

Results

Karyotyping identified 75 sSMCs in 74,266 samples (0.1% incidence). The chromosomal origins of 27 of these sSMCs were detected by sequencing-related techniques (NGS, MLPA and STR). Eight of these sSMCs are being reported for the first time. sSMCs mainly derived from chromosomal X, Y, 15, and 18, and some sSMC chromosomal origins could be correlated with clinical phenotypes. However, the chromosomal origins of the remaining 48 sSMC cases are unknown. Thus, we will develop a set of economical and efficient methods for clinical sSMC diagnosis.

Conclusions

This study details the comprehensive characterization of 27 sSMCs. Eight of these sSMCs are being reported here for the first time, providing additional information to sSMC research. Identifying sSMCs may reveal genotype-phenotype correlations and integrate genomic data into clinical care.

Noninvasive prenatal testing aids identification of tetrasomy 18p: A case report

Tetrasomy 18p syndrome (Online Mendelian Inheritance in Man 614290) is a rare chromosomal disorder that is seen in approximately 1 in every 180,000 live births. It is caused by the presence of isochromosome 18p, which is a supernumerary marker composed of two copies of the short arms of chromosome 18. Isochromosome 18p is one of the most commonly observed isochromosomes. We report tetrasomy 18p syndrome diagnosed prenatally after noninvasive prenatal testing (NIPT) was positive for trisomy 18. Tetrasomy 18p was finally diagnosed by G-banding and fluorescence in situ hybridization of chromosome 18p, before invasive confirmatory testing the karyotype findings by NIPT showed an increase in the DNA fragments from chromosome 18p, indicating duplication of chromosome 18p. NIPT can detect not only trisomy 13, 18, and 21, but also structural chromosomal anomalies, such as deletions and duplications. An NIPT report "positive for trisomy 18" indicates the possibility of tetrasomy 18p, and detailed analysis of NIPT data can reveal subchromosomal copy number variations, to a certain extent, before definitive diagnostic testing.

Clinical and molecular findings in nine new cases of tetrasomy 18p syndrome: FISH and array CGH characterization

BACKGROUND

Small Supernumerary Marker Chromosomes (sSMC) are rare chromosomal abnormalities, which have abnormal banding arrangement and take many shapes. Several disorders have been correlated with sSMC presence. The aim of this study is to characterize the sSMC derived from chromosome 18 by Fluorescence in situ hybridization (FISH) and Array Comparative Genomic Hybridization (aCGH).

RESULTS

Nine children with dysmorphic features have been investigated. They have these features in common: a triangular face, low-set ears, a large mouth with a thin upper lip, and a horizontal palpebral fissure. Epicanthus and strabismus were present in two patients. In addition, we have noticed microcephaly and mental and/or developmental delay with low birth weight. However, two patients had standard birth weight; one patient had hypospadias; two had skin problems; and three showed different congenital heart defects. One patient had corpus callosum hypoplasia. Systematic karyotype analysis revealed a de novo supernumerary chromosome. Array CGH showed a gain in copy number on the short arm of chromosome 18 in the nine cases. In one case, the sSMC seemed to be in mosaic. The breakpoints of the marker were identified using aCGH and FISH. Thus, the sSMC led to 18p tetrasomy with approximately 14 Mb lengths, between 364344 and 14763575 based on the human genome version 18.

CONCLUSIONS

These results have been completed by FISH in order to ascertain the shape of the sSMC. Our results confirm the uniqueness and particularity of the iso18p syndrome on the phenotypic as well as on the genetic level.

Abnormal bone mineral content and density in people with tetrasomy 18p

Tetrasomy 18p is a rare chromosomal abnormality, resulting from an additional iso-chromosome composed of two copies of the short arm. It is characterized by craniofacial abnormalities, neuromuscular dysfunction, and developmental delay. The Chromosome 18 Clinical Research Center has established the largest cohort of individuals with this rare genetic condition. Here, we describe a case series of 21 individuals with tetrasomy 18p who have a previously unreported clinical finding: low bone mineral density. Most individuals met criteria for low bone density despite being relatively young (mean age of 21 years). Clinicians providing care to individuals affected by Tetrasomy 18p should be aware of their increased risk for decreased bone density and pathological fractures.

Tetrasomy 18p: The challenges of noninvasive prenatal testing and combined test

Circulating cell-free DNA, having no procedural risk of miscarriage, is the most suitable sample for a noninvasive prenatal testing (NIPT). Here we report on a boy, who came to our attention for hypotonia and psychomotor delay when he was 16 months old. During the pregnancy his mother performed a NIPT that resulted compatible with the presence of trisomy 18. A confirmatory invasive procedure has been proposed, but not performed, because the family preferred to follow a conservative line. A series of ultrasound excluded the presence of any major malformations. Genetic tests, performed after birth, revealed the presence of a tetrasomy 18p with an extra isochromosome 18p. Our report wants to underline the importance of an invasive procedure and consequent cytogenetic analysis in case of NIPT results indicating autosomal trisomies because under it may hide the presence of other structural chromosomal anomalies. These conditions are normally not visible at prenatal ultrasound or using combined test (CT) and the only identifiable not invasive sign could be the results of high risk at NIPT.

Strukturelle Chromosomenstörungen bei Intelligenzminderung

Strukturelle und numerische Chromosomenstörungen gehören zu den häufigen Ursachen der Intelligenzminderung und psychomotorischen Entwicklungsstörung. Die große Heterogenität der Intelligenzminderung spiegelt sich auch in der Vielfalt möglicher Aberrationstypen und ursächlicher Chromosomenregionen wider. Die konventionelle lichtmikroskopische Zytogenetik kann hierbei u. a. strukturelle Aberrationen mit Größen über ca. 5–10 Megabasenpaaren (Mb) auch in Form kleinerer Mosaike nachweisen und diese im Genom lokalisieren. Durch Fluoreszenz-in situ-Hybridisierung können bei klinischem Verdacht gezielt auch deutlich kleinere Aberrationen, z. B. Mikrodeletionen, detektiert werden. Chromosomale Mikroarrays (CMA) detektieren dank ihrer besseren Auflösung, die bis deutlich unter 0,1 Mb reichen kann, genomweit submikroskopische Mikrodeletionen und Mikroduplikationen, machen jedoch bei Duplikationen keine Aussage zu deren genomischer Lokalisation und können meist niedriggradige Mosaike unter 20 % kaum nachweisen. Zytogenetik und CMA ergänzen sich aufgrund ihrer unterschiedlichen Fähigkeiten und weisen einschließlich der Trisomie 21 jeweils in ungefähr 15 % der Patienten mit Intelligenzminderung ursächliche Chromosomenaberrationen nach. Sie stellen damit neben aktuellen Sequenzierungstechniken ein wichtiges Element der humangenetischen Ursachenabklärung bei Intelligenzminderung dar. Typische chromosomale Aberrationstypen werden beispielhaft besprochen und in das heutige Gesamtbild eingeordnet.

Prenatal diagnosis and molecular cytogenetic characterization of low-level mosaicism for tetrasomy 18p at amniocentesis in a pregnancy with a favorable outcome

OBJECTIVE

We present prenatal diagnosis of low-level mosaicism for tetrasomy 18p at amniocentesis in a pregnancy with a favorable outcome.

CASE REPORT

A 40-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a de novo supernumerary isochromosome 18p in eight of 39 colonies of cultured amniocytes. The karyotype was 47,XX,+i(18)(p10)[8]/46,XX[31]. Array comparative genomic hybridization (aCGH) analysis using uncultured amniocytes revealed arr 18p11.32p11.21 [hg 19] (148,963-14,081,887) × 2-3. Repeat amniocentesis was performed at 20 weeks of gestation. Interphase fluorescence in situ hybridization (FISH) analysis showed four 18p11.22-specific probe (RP11-918F20) signals in 11.7% (12/103 cells) of uncultured amniocytes. aCGH analysis on uncultured amniocytes did not detect genomic imbalance in chromosome 18. The parental karyotypes were normal. Polymorphic DNA marker analysis excluded uniparental disomy 18. Cytogenetic analysis of cultured amniocytes at repeat amniocentesis revealed a karyotype of 47,XX,+i(18)(p10)[2]/46,XX[12]. Prenatal ultrasound was unremarkable. The pregnancy was carried to 38 weeks of gestation, and a 2742-g phenotypically normal female baby was delivered with a cord blood karyotype of 46,XX. When examined at 8 months of age, the infant was normal in growth and psychomotor development. Interphase FISH analysis on 21 uncultured urinary cells revealed normal signals in all cells and no mosaic tetrasomy 18p.

CONCLUSION

Low-level mosaic tetrasomy 18p at amniocentesis without ultrasound abnormalities can be associated with a favorable outcome.

Tetrasomy 18p: case report and review of literature

Tetrasomy 18p syndrome (Online Mendelian Inheritance in Man 614290) is a very rare chromosomal disorder that is caused by the presence of isochromosome 18p, which is a supernumerary marker composed of two copies of the p arm of chromosome 18. Most tetrasomy 18p cases are de novo cases; however, familial cases have also been reported. It is characterized mainly by developmental delays, cognitive impairment, hypotonia, typical dysmorphic features, and other anomalies. Herein, we report de novo tetrasomy 18p in a 9-month-old boy with dysmorphic features, microcephaly, growth delay, hypotonia, and cerebellar and renal malformations. We compared our case with previously reported ones in the literature. Clinicians should consider tetrasomy 18p in any individual with dysmorphic features and cardiac, skeletal, and renal abnormalities. To the best of our knowledge, we report for the first time an association of this syndrome with partial agenesis of cerebellar vermis.

Tetrasomy 18p in a Twin Pregnancy with Diverse Expression in Both Fetuses

Tetrasomy 18p, characterized by the presence of four copies of the short arm of chromosome 18, is considered to occur with the nondisjunction in meiosis II after the errors in the meiotic and early postmeiotic mitotic division in the centromere. It is accompanied by various abnormalities including congenital heart defects, lower extremity abnormalities, micrognathia, high arched palate, kyphoscoliosis, microcephaly, myelomeningocele, hernia and renal anomalies. We present the first case of a dichorionic diamniotic twin pregnancy in which both fetuses were affected by tetrasomy 18p, but with discordant morphology, detected in one twin in the first but in the other in the second trimester.

Tetrasomy 18p: report of cognitive and behavioral characteristics

Our purpose was to describe intellectual and behavioral characteristics of persons with tetrasomy 18p. This is a more detailed investigation into the cognitive and behavioral characteristics of our previously reported tetrasomy 18p cohort of 43 plus six additional participants. We evaluated the intellectual functioning using standard measures of cognitive ability, measures of executive functioning, adaptive and maladaptive behaviors. Intellectual abilities ranged from mild impairment/borderline normal to severe/profound impairment calling into question the assumption that severe cognitive limitation is always a feature of tetrasomy 18p. For persons with tetrasomy 18p with mild cognitive deficits, the main barriers to successful functioning stems from limited social and metacognitive skill development and behavior regulation problems rather than being solely determined by cognitive deficits alone.

Adults with Chromosome 18 Abnormalities

The identification of an underlying chromosome abnormality frequently marks the endpoint of a diagnostic odyssey. However, families are frequently left with more questions than answers as they consider their child's future. In the case of rare chromosome conditions, a lack of longitudinal data often makes it difficult to provide anticipatory guidance to these families. The objective of this study is to describe the lifespan, educational attainment, living situation, and behavioral phenotype of adults with chromosome 18 abnormalities. The Chromosome 18 Clinical Research Center has enrolled 483 individuals with one of the following conditions: 18q-, 18p-, Tetrasomy 18p, and Ring 18. As a part of the ongoing longitudinal study, we collect data on living arrangements, educational level attained, and employment status as well as data on executive functioning and behavioral skills on an annual basis. Within our cohort, 28 of the 483 participants have died, the majority of whom have deletions encompassing the TCF4 gene or who have unbalanced rearrangement involving other chromosomes. Data regarding the cause of and age at death are presented. We also report on the living situation, educational attainment, and behavioral phenotype of the 151 participants over the age of 18. In general, educational level is higher for people with all these conditions than implied by the early literature, including some that received post-high school education. In addition, some individuals are able to live independently, though at this point they represent a minority of patients. Data on executive function and behavioral phenotype are also presented. Taken together, these data provide insight into the long-term outcome for individuals with a chromosome 18 condition. This information is critical in counseling families on the range of potential outcomes for their child.

Clinical impact of proximal autosomal imbalances

Centromere-near gain of copy number can be induced by intra- or inter-chromosomal rearrangements or by the presence of a small supernumerary marker chromosome (sSMC). Interestingly, partial trisomy to hexasomy of euchromatic material may be present in clinically healthy or affected individuals, depending on origin and size of chromosomal material involved. Here we report the known minimal sizes of all centromere-near, i.e., proximal auto-somal regions in humans, which are tolerated; over 100 Mb of coding DNA are comprised in these regions. Additionally, we have summarized the typical symptoms for nine proximal autosomal regions including genes obviously sensitive to copy numbers. Overall, studying the carriers of specific chromosomal imbalances using genomics-based medicine, combined with single cell analysis can provide the genotype-phenotype correlations and can also give hints where copy-number-sensitive genes are located in the human genome.

Prenatal diagnosis of mosaic tetrasomy 18p

OBJECTIVE

To present prenatal diagnosis and molecular cytogenetic characterization of a small supernumerary marker chromosome derived from isochromosome 18p, by interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes.

CASE REPORT

A 41-year-old woman underwent amniocentesis at 18 weeks of gestation, because of advanced maternal age. Amniocentesis revealed a de novo supernumerary isochromosome 18p in two of 14 colonies of cultured amniocytes. Repeated amniocentesis was performed at 22 weeks of gestation. Interphase FISH analysis on uncultured amniocytes showed four 18p11.32-specific probe (RP11-324G2) signals in 5.7% (3/53 cells) of uncultured amniocytes. A multiplex ligation-dependent probe amplification P095 test kit and array comparative genomic hybridization analysis did not detect genomic imbalance in chromosome 18. Cytogenetic analysis of cultured amniocytes at repeated amniocentesis revealed a karyotype of 47,XY,+i(18)(p10)[3]/46,XY[23]. The pregnancy was carried to 38 weeks of gestation, and a healthy 3120 g male baby was delivered. When examined at 2 months of age, the infant was normal in growth and development, without phenotypic abnormalities. The cord blood had a karyotype of 46,XY. Polymorphic DNA marker analysis excluded uniparental disomy 18. Interphase FISH analysis on uncultured urinary cells showed 9.4% (3/32 cells) mosaicism for tetrasomy 18p.

CONCLUSION

There is cytogenetic discrepancy between amniocytes and cord blood lymphocytes in prenatally detected mosaic tetrasomy 18p. Interphase FISH on uncultured amniocytes has the advantage of rapid confirmation of low-level mosaicism for tetrasomy 18p at amniocentesis.

A case report of prenatally diagnosed tetrasomy 18p

Tetrasomy 18p, one of the most commonly observed isochromosomes, consists of two copies of the p arms on chromosome 18[i(18p)]. It is known as a de novo occurrence of non-disjunction or centromeric mis-division during meiosis II in the vast majority of cases. It has a prevalence of 1/140,000-180,000 live births and affects both genders equally. A 28-year-old woman was referred at 33+2 weeks gestation to rule out fetal congenital heart disease. Her prenatal ultrasonography showed intrauterine growth retardation, cardiomegaly, and imperforate anus. Doppler ultrasonographic finding showed fetal anemia. Tetrasomy 18p was confirmed by conventional karyotyping and fluorescence in situ hybridization. Because of its very low prevalence rate, only several cases of tetrasomy 18p has been reported worldwide and it has not yet been reported in Korea before. Therefore, we report a case of prenatally diagnosed tetrasomy 18p.

Secondary findings from non-invasive prenatal testing for common fetal aneuploidies by whole genome sequencing as a clinical service

OBJECTIVE

To report secondary or additional findings arising from introduction of non-invasive prenatal testing (NIPT) for aneuploidy by whole genome sequencing as a clinical service.

METHODS

Five cases with secondary findings were reviewed.

RESULTS

In Case 1, NIPT revealed a large duplication in chromosome 18p, which was supported by arrayCGH of amniocyte DNA, with final karyotype showing mosaic tetrasomy 18p. In Case 2, a deletion in the proximal long arm of chromosome 18 of maternal origin was suspected and confirmed by arrayCGH of maternal white cell DNA. In Case 3, NIPT was negative for trisomies 21 and 18. In-depth analysis for deletions/duplications was requested when fetal structural anomalies were detected at routine scan. A deletion in the proximal long arm of chromosome 3 was found and confirmed by karyotyping. In Case 4, NIPT correctly predicted confined placental mosaicism with triple trisomy involving chromosomes X, 7 and 21. In Case 5, NIPT correctly detected a previously unknown maternal mosaicism for 45X.

CONCLUSION

Non-invasive prenatal testing is able to detect a wide range of fetal, placental and maternal chromosomal abnormalities. This has important implications on patient counseling when an abnormality is detected by NIPT.

[Tetrasomy 18p syndrome and hearing loss. An unusual case]

Tetrasomy 18p is a rare chromosomal disease (1:140,000 live births), which affects females and males equally, and might be hereditary or caused by spontaneous changes (de novo formation) within the chromosome. The phenotype results from the presence of a small extra metacentric marker chromosome, an isochromosome 18p. The syndrome is characterized by mild-to-moderate mental retardation, poor language acquisition, seizures, microcephaly, short statue, minor facial dysmorphic features, congenital heart diseases, uro/renal malformations, abnormal muscle tone, spasticity of the lower limbs, and delayed ability to stand and walk. To our knowledge sensorineural hearing loss is described in the literature but has not been described as a typical phenotypic symptom of tetrasomy 18p.In the following report, a boy with tetrasomy 18p is described. In addition to psychomotor retardation with muscular hypotonia and orofacial dismorphysms, bilateral severe hearing loss was diagnosed. Thus, in all infants with known chromosomal aberration, early diagnostic procedures must be performed to unveil sensorineural hearing loss that might be overseen because of mental retardation. In particular, a brainstem-evoked response audiometry (BERA) should be considered for early diagnosis and treatment of possible hearing loss. Furthermore, in all children with developmental delay and dysmorphic features a chromosomal analysis should be initiated.

Severe cervical scoliosis in the fetus

OBJECTIVE

This study provides prenatal characteristics and postnatal outcomes of patients with severe cervical scoliosis.

METHODS

A retrospective analysis of clinical information from cases prenatally diagnosed with severe cervical scoliosis (>90° angulation) in the Fetal Care Center at Cincinnati Children's Hospital Medical Center between 2007 and 2010 was performed. We excluded iniencephaly and tumors of the head or neck.

RESULTS

We identified five patients with severe cervical scoliosis. The fetal spine abnormality was diagnosed between 18 and 27 weeks of gestation. Classical cesarean section was recommended in all patients. There were no immediate airway or neurological complications in the delivery room. Extravertebral anomalies were present in four of the five patients. These patients had a more complicated clinical course and three separate syndromes including a complex collagenopathy, heterotaxy, and Klippel-Feil syndrome were identified. One patient had an isolated cervical deformation secondary to a large uterine fibroid with a benign clinical course. None of the infants have required spinal surgery.

CONCLUSION

Our patients suggest that connective tissue diseases or heterotaxy may be important risk factors for the development of severe cervical scoliosis. There were no significant long-term complications directly related to cervical scoliosis.

Ophthalmic manifestations of tetrasomy 18p

PURPOSE

To characterize ophthalmic findings in patients with tetrasomy 18p, a rare chromosomal anomaly that has been previously associated with strabismus.

METHODS

All subjects underwent a complete eye examination to screen for ocular pathology.

RESULTS

A total of 25 subjects (13 female) were examined after they were diagnosed with tetrasomy 18p. The average age of subjects was 8.2 years (range, 13 months to 22 years). Of the 25 subjects, 18 (72% of examined subjects, 42% of the cohort) showed evidence of strabismus; 16 had esotropia (8 uncategorized, 5 infantile, and 3 accommodative), 1 had esophoria, and 1 was diagnosed with intermittent exotropia.

CONCLUSIONS

The coincidence of esotropia with tetrasomy 18p indicates the need to routinely screen these patients for strabismus at the time of diagnosis.