Tetrasomy 18p in a male dysmorphic child in southeast Turkey

The behavioral phenotype in a cohort of patients with chromosome 18 anomalies: a retrospective observational study

BACKGROUND

Genetic syndromes resulting from chromosome 18 structural abnormalities constitute a broad spectrum of conditions characterized by significant clinical heterogeneity. Most studies in the literature focus on case reports and clinical observations; the present study aims to assess the cognitive, communicative, behavioral, and adaptive abilities of different chromosome 18 abnormalities. In addition, this work aims to identify phenotype-genotype correlations by comparing individuals with 18p deletion, 18q deletion, and 18p tetrasomy.

METHODS

The sample included 24 patients with a definite genetic diagnosis of 18p deletion (N = 6), 18q deletion (N = 9), or 18p tetrasomy (N = 8). The assessment is provided by using a specific protocol based on direct and indirect clinical assessment of patients. Differences in IQ/GQ indexes, adaptive behavior, CARS scores, and CBCL internalizing and externalizing symptoms were assessed using ANCOVAs with age as covariate.

RESULTS

Our results showed more significant cognitive and behavioral impairment in tetrasomy 18 than in the other two conditions. Conversely, in 18p deletion group, we found greater behaviorally susceptibility to develop autistic traits.

CONCLUSION

These preliminary findings should raise clinicians' awareness of the strengths and weaknesses of patients with chromosome 18 alterations, paving the way to targeted and more appropriate management.

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.].

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: 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.

Characterization of sSMC by FISH and molecular techniques

Small supernumerary marker chromosome (sSMC) is a structurally altered additional chromosome that may not be explicitly clarified by conventional karyotyping alone. About one third of sSMC carriers have abnormal phenotypes and its clinical correlation is difficult, especially in prenatal studies. The present study was aimed at characterizing 19 sSMC identified in 15 patients with dysmorphic features with or without multiple congenital anomalies, conspicuous family history, short stature and/or ambiguous genitalia. All the sSMC were primarily identified by routine cytogenetics studies (performed with banding techniques) from peripheral blood except in one patient, where amniotic fluid was used. All sSMCs were further characterized by array-CGH (using 44 K oligonucleotide probe) and/or fluorescence in situ hybridization (FISH) using multicolor banding (MCB), centromere specific multicolor FISH (cenM-FISH), subcentromere-specific multicolor FISH (subcenM-FISH), micro-dissection and/or reverse FISH. This report demonstrates the worth of advanced molecular (cyto)genetic techniques in characterizing sSMC, their utility in genotype-phenotype correlation and risk of clinical presentation.

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

Thus far, the phenotype of tetrasomy 18p has been primarily delineated by published case series and reports. Findings reported in more than 25% of these cases include neonatal feeding problems, growth retardation, microcephaly, strabismus, muscle tone abnormalities, scoliosis/kyphosis, and variants on brain MRI. Developmental delays and cognitive impairment are universally present. The purpose of this study was to more fully describe tetrasomy 18p at both the genotypic and the phenotypic levels. Array CGH was performed on 43 samples from individuals with tetrasomy 18p diagnosed via routine karyotype. The medical records of 42 of these 43 individuals were reviewed. In order to gain additional phenotypic data, 31 individuals with tetrasomy 18p underwent a series of clinical evaluations at the Chromosome 18 Clinical Research Center. Results from the molecular analysis indicated that 42 of 43 samples analyzed had 4 copies of the entire p arm of chromosome 18; one individual was also trisomic for a section of proximal 18q. The results of the medical records review and clinical evaluations expand the phenotypic description of tetrasomy 18p to include neonatal jaundice and respiratory distress; recurrent otitis media; hearing loss; seizures; refractive errors; constipation and gastroesophageal reflux; cryptorchidism; heart defects; and foot anomalies. Additional findings identified in a small number of individuals include hernias, myelomeningocele, kidney defects, short stature, and failure to respond to growth hormone stimulation testing. Additionally, a profile of dysmorphic features is described. Lastly, a series of clinical evaluations to be considered for individuals with tetrasomy 18p is suggested.