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Partial hexasomy of chromosome 15.
1Genzyme Genetics, Orange, California 92869, USA. bihuang@genzyme.com
American Journal of Medical Genetics. Part A
|August 19, 2003
Summary
Marker chromosomes, specifically inv dup(15), are common. This study details an infant with two copies of a large inv dup(15), resulting in hexasomy for the Prader-Willi/Angelman syndrome region, leading to severe developmental and neurological issues.
Area of Science:
- Genetics
- Human Chromosomes
- Developmental Biology
Background:
- Marker chromosomes, particularly inv dup(15), are the most frequent type in humans.
- Large inv dup(15) markers containing the Prader-Willi syndrome (PWS)/Angelman syndrome (AS) region are linked to significant neurodevelopmental abnormalities.
Observation:
- A 10-day-old infant presented with infantile spasms, microcephaly, hypotonia, and lethargy.
- Karyotype analysis revealed 48,XY, +2mar, indicating two extra marker chromosomes.
- Fluorescence in situ hybridization confirmed both markers originated from chromosome 15 and encompassed the PWS/AS critical region.
Findings:
- The infant possessed two large inv dup(15) markers, resulting in hexasomy for the PWS/AS region.
- Initial phenotype at birth was not markedly more severe than expected for a single large inv dup(15).
- By 21 months, the patient exhibited severe seizures, bilateral hearing loss, and cortical blindness.
Implications:
- This case highlights the potential for severe neurodevelopmental outcomes in individuals with hexasomy for the PWS/AS region due to inv dup(15).
- The study underscores the importance of detailed chromosomal analysis and long-term follow-up for characterizing the phenotypic spectrum of inv dup(15) rearrangements.
- Understanding the impact of increased dosage in the PWS/AS region is crucial for genetic counseling and clinical management.