Partial trisomy 6p

Partial trisomy 6p is a rare chromosomal anomaly associated with low birth weight, developmental delay, craniofacial abnormalities, feeding difficulties, congenital heart defects and renal abnormalities. In most previously reported cases trisomy 6p was associated with the partial monosomy of another chromosome, often due to parental balanced translocation. This further contributes to the difficulty of understanding the genotype-phenotype relationship of this condition. Pure partial trisomy 6p cases are even rarer; the authors find 22 pre-existing cases, and only the distal segments of 6p (6p25-pter) were duplicated in the significant part of the known “pure” cases. Türkyılmaz et al. reports a 2-year-old girl with prenatal hypoplasia, growth retardation, microcephaly, blepharophimosis, craniofacial dysmorphism, hearing loss, atrial septal defect, and primary congenital hypothyroidism. Cytogenetic analysis showed this patient’s G-banded karyotype to be 46,XX,der(2)t(2;6)(q37.3;p22.1). Through SNP-array analysis, the 27.5 Mb extra chromosomal material detected in chromosome 2 was determined to have originated from a heterozygous duplication at 6p25.3p22.1. The translocation was sporadic, and there was no evidence for the loss of genetic material of 2q37.3. Through the clinical findings of pure partial trisomy 6p in previous literature and in the current case, the most common findings included prominent forehead, microcephaly, developmental delay, cardiac and renal anomalies, and brain malformations. In the present case, hyperintensity at pons and dilation in both lateral ventricles and the third ventricle was observed in her brain MRI. These manifestations are a brain anomaly for pure partial trisomy 6p. The proband is also the second reporting of a hyperthyroidism phenotype, suggesting that this is a rare feature. The hypothyroidism phenotype detected in the patient may be associated with the SLC17A4 and EDN1 genes involved in thyroid development and function and located in the duplication region. Overall this case study contributes to our understanding of pure partial trisomy 6p’s phenotypic spectrum by clarifying its rare manifestations.

Türkyılmaz et al. “De novo Pure Partial Trisomy 6p Associated with Facial Dysmorphism, Developmental Delay, Brain Anomalies, and Primary Congenital Hypothyroidism”. “Molecular Syndromology” 2022.

Chromosome Disorder Outreach Inc. medical geneticist and medical advisor Dr. Iosif Lurie M.D. Ph.D examines newly published research studies to locate the most important and relevant for our members. Synopses of these articles are then posted to our website’s research pages. For more information on any article please contact info@chromodisorder.org