Tetrasomy 18p: case report and review of literature

Consanguinity and Occurrence of Monogenic Diseases in a Single Tertiary Centre in Riyadh, Saudi Arabia: A 2 Years Cross-Sectional Study

Background

Consanguinity, or the practice of marrying close relatives, is a common cultural tradition in Saudi Arabia, with rates among the highest in the world. This practice has significant implications for the prevalence and distribution of major single genetic defects and chromosomal abnormalities within the Saudi population.

Methods

Herein, using the BESTCare electronic medical record system (designed to streamline hospital operations, enhance patient care, and improve the overall efficiency of healthcare services; bestcare.ezcaretech.com) in a single tertiary centre, King Abdullah Specialized Children Hospital (KASCH) in Riyadh, Saudi Arabia, we performed a cross-sectional study for all patients referred to the hospital from the 1st January 2020 until 1st January 2022.

Results

The present study, which included 1100 individuals, found a high prevalence of consanguinity (64%) and a significant proportion of third-degree relatives (69%). The mean age of participants was 12.24 years, and the diagnostic rate using advanced molecular genetics techniques was 45%, with whole exome sequencing (WES) being the most common method (43%). The study also noted a significant delay in diagnosis for more than a year in 16% of cases, with a common neurodevelopmental phenotype (18%).

Conclusion

In conclusion, we revealed the prevalence of consanguineous marriages in the KASCH hospital in Riyadh, Saudi Arabia. We also highlighted the most frequently referred phenotype. These findings are consistent with previous research on the prevalence and impact of consanguinity on rare genetic disorders.

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.

Molecular delineation of de novo small supernumerary marker chromosomes in prenatal diagnosis, a retrospective study

OBJECTIVES

To define the genotype-phenotype correlation of small supernumerary marker chromosomes (sSMCs) and conduct precise genetic counseling, we retrospectively searched and reviewed de novo sSMCs cases detected during prenatal diagnosis at The First Affiliated Hospital of Zhengzhou University.

MATERIALS AND METHODS

Chromosome karyotypes of 20,314 cases of amniotic fluid from pregnant women were performed. For 16 samples with de novo sSMCs, 10 were subjected to single-nucleotide polymorphism (SNP) array or low-coverage massively parallel copy number variation sequencing (CNV-seq) analysis.

RESULTS

Among the 10 sSMCs cases, two sSMCs derived from chromosome 9, and three sSMCs derived from chromosomes 12, 18 and 22. The remaining 5 cases were not identified by SNP array or CNV-seq because they lacked euchromatin or had a low proportion of mosaicism. Four of them with a karyotype of 47,XN,+mar presented normal molecular cytogenetic results (seq[hg19] 46,XN), and the remaining patient with a karyotype of 46,XN,+mar presented with Turner syndrome (seq[hg19] 45,X). Five sSMCs samples were mosaics of all 16 cases.

CONCLUSION

Considering the variable origins of sSMCs, further genetic testing of sSMCs should be performed by SNP array or CNV-seq. Detailed molecular characterization would allow precise genetic counseling for prenatal diagnosis.

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.

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.].

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.

A novel heterozygous duplication of the SLC12A3 gene in two Gitelman syndrome pedigrees: indicating a founder effect

Gitelman syndrome is an autosomal recessive salt-wasting tubulopathy caused by mutations in the SLC12A3 gene. A female and a male sibling from two unrelated Greek-Cypriot families presenting with a severe salt-wasting tubulopathy due to compound heterozygous mutations of a novel duplication and a previously reported missense mutation in the SLC12A gene are described. Sanger sequencing was used to identify possible mutations in the SLC12A3 gene. For the detection of duplications/conversions and deletions in the same gene, Multiplex ligation probe amplification (MLPA) analysis was performed. Direct sequencing and MLPA analysis of the SLC12A3 gene identified two compound heterozygous mutations in both unrelated probands. Both probands were identified to carry in compound heterozygosity the known p.Met581Lys and a novelheterozygous duplication of exons 9-14 (E9_E14dup). The diagnosis of Gitelman syndrome was made through clinical assessment, biochemical screening and genetic analysis. The identification of the novel SLC12A3 duplication seems to be characteristic of Greek-Cypriot patients and suggests a possible ancestral mutational event that has spread in Cyprus due to a possible founder effect. Testing for Gitelman syndrome probable variants can be performed before proceeding to a full gene sequencing dropping the diagnostic cost. In addition, this report adds to the mutational spectrum observed.

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.