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.

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.].

Two-Generation Transmission of Trisomy 18p: Prenatal Diagnosis in a Woman with Mild Intellectual Disability

Trisomy 18p is a rarely observed chromosomal aberration. Only 31 cases have previously been described in the literature. Trisomy 18p is associated with mild to moderate phenotypic anomalies and intellectual disability. Here, we report on a pregnant woman in whom noninvasive prenatal testing indicated a high risk of fetal trisomy 18. Prenatal diagnosis and karyotyping of the parents were performed and demonstrated that both the mother and the fetus had a derivative chromosome 15 with a segment of unknown origin. Chromosomal microarray analysis and FISH revealed a 14.9-Mb duplication of 18p and detected 3 centromeres of chromosome 18. To our knowledge, this is the first study reporting trisomy 18p due to an unbalanced translocation of 18p onto chromosome 15q showing 2-generation transmission. The results suggest that trisomy 18p can be considered a euchromatic variant.