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Trisomy 7p resulting from isochromosome formation and whole-arm translocation
I W Lurie1, M F Schwartz, S Schwartz
1Department of Pediatrics, School of Medicine, University of Maryland at Baltimore, USA.
Insights
A rare genetic condition involving trisomy 7p in a newborn boy presented with a large anterior fontanel and developmental delay. This case highlights the complex genetic rearrangements leading to partial trisomies.
Area of Science:
- Genetics
- Developmental Biology
- Pediatrics
Background:
- Partial trisomies, particularly those involving chromosome 7p, can lead to a spectrum of congenital anomalies.
- Understanding the genetic basis of these anomalies is crucial for diagnosis and management.
Observation:
- A newborn presented with a large anterior fontanel, minor facial anomalies, postaxial polydactyly, patent ductus arteriosus, and developmental delay.
- Karyotyping revealed trisomy 7p due to an isochromosome i(7p) and a translocation t(2;7)(q37.3;q11.1).
Findings:
- Enlarged anterior fontanel is a characteristic finding in duplications of 7p15-pter.
- Brain asymmetry and posterior fossa defects are associated with duplications of 7p11-p12.
- Cardiac defects are common, occurring in over 50% of patients with 7p duplications.
Implications:
- Isochromosome formation with whole-arm translocation is an exceptionally rare mechanism for partial trisomies, potentially involving uniparental isodisomy.
- The sequence of these complex rearrangements may have adaptive significance, warranting further investigation.
Abstract:
A newborn boy with a large anterior fontanel, minor facial anomalies, postaxial polydactyly, patent ductus arteriosus, and developmental delay had trisomy of 7p due to an i(7p) and a concomitant t(2;7) (q37.3;q11.1). Significant enlargement of the fontanel is the most characteristic finding in most patients with duplications involving 7p15-pter. Asynchrony in fore- and hindbrain and hemisphere formation leading to brain asymmetry and various defects in the posterior fossa are typical of infants with duplications of 7p11-p12. A variety of heart defects has also been found in more than 50% of patients with duplication of 7p segments. Isochromosome formation accompanied by whole-arm translocation, resulting in uniparental isodisomy for the involved segment, is an extremely rare cause leading to partial trisomies. Although it is not clear whether isochromosome formation precedes the whole-arm translocation or follows it, the secondary rearrangement may have adaptive significance.