Tetrasomy 6p caused by a small supernumerary marker chromosome presenting Trisomy distal 6p Phenotype.
A small supernumerary marker chromosome (sSMC) is a structurally abnormal additional chromosome that most often lacks a distinct banding pattern and is difficult to identify by conventional banding cytogenetic analysis. Approximately 70% of such chromosomes occur de novo; 30% are mosaic. Partial tetrasomy of chromosome 6p is extremely rare and there is only one previously reported case in literature. Syu et al. present a male infant with developmental delay, microcephaly, dysgenesis of the anterior eye segment, corneal opacity, choanal atresia, hearing defects, preauricular pit, congenital heart defects (atrio-ventricular communication, atrial septal defect, pulmonary stenosis), hypoplastic kidneys, hydronephrosis, vesico-ureteral reflux, hypospadias, sacral sinus and facial dysmorphism. This child had de novo mosaic tetrasomy 6p23-p25.3 caused by an sSMC. The tetrasomic segment contained 14.337 Mb of terminal 6p and included genes FOXC1 and BMP6. The gene BMP6 is located at 6p24.3 and encodes bone morphogenic protein 6, which is involved in bone formation. FOXC1 is located at 6p25.3 and has been shown to play a role in the regulation of embryonic and ocular development; it has recently been suggested that FOXC1 variants causes dysgenesis of the anterior eye segment and cardiac anomalies. The anterior segment dysgenesis and glomerulopathy phenotype in this patient causes the authors to suggest triplosensitivity of the FOXC1 gene. To better understand the clinical manifestation of the rare partial 6p tetrasomy, the authors compare the current case with phenotypes in previously reported patients with trisomy and tetrasomy of 6p23-p25.3. For example, distal 6p trisomy is associated with low birth weight, developmental delay, growth retardation, mild to severe craniofacial abnormalities, feeding difficulties, recurrent infections, neurological anomalies, congenital heart defects, and renal abnormalities, similar to manifestations in the present patient. Thus, the current patient demonstrates that the phenotype of mosaic tetrasomy distal 6p was comparable to that of distal 6p trisomy. The authors suggest that an array-CGH evaluation should be performed for associated syndromic disease to better show the genetic content of sSMCs.
Syu et al. “De Novo Mosiac 6p23-p25.3 Tetrasomy Caused by a Small Supernumerary Marker Chromosome Presenting Trisomy Distal 6p Phenotype: A Case Report and Literature Review”. “Diagnostics” 2022, v.12:2306.
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