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Familial 14-Mb deletion at 21q11.2-q21.3 and variable phenotypic expression
Keiko Wakui1, Atsushi Toyoda, Takeo Kubota
1Department of Medical Genetics, Shinshu University School of Medicine, Matsumoto, Japan.
Journal of Human Genetics
|October 12, 2002
Summary
A familial deletion on chromosome 21q was identified in a phenotypically normal mother and her two affected children. This deletion may unmask genes contributing to sensorineural hearing loss and mental retardation.
Area of Science:
- Genetics
- Human Molecular Genetics
Background:
- Familial interstitial deletion of chromosome 21q (del(21q)) can present with variable phenotypes.
- Understanding the precise breakpoints and genetic consequences is crucial for diagnosing and counseling affected families.
Observation:
- A phenotypically normal mother carried a proximal interstitial deletion of chromosome 21q.
- Her first child exhibited sensorineural hearing loss and moderate mental retardation; the second child had mild mental retardation without hearing loss.
Findings:
- Fluorescence in situ hybridization and molecular analysis mapped the deletion to approximately 14 Mb within 21q11.2-q21.3.
- Both affected children inherited the same maternal del(21q) haplotype, with a crossover noted on the paternal chromosome 21.
Implications:
- The deletion may unmask deleterious genes on the paternal chromosome 21, influencing the severity of intellectual disability and hearing loss.
- Usher syndrome 1E is a potential candidate locus for the sensorineural hearing loss observed in the first child.