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Duplication of 7p21.2-->pter due to maternal 7p;21q translocation: implications for critical segment assignment in
1National Laboratory of Medical Genetics, Hunan Medical University, P. R. China. tao.cai@nih.gov
Insights
This study details a rare genetic condition in a 1-year-old boy, identifying an unbalanced translocation involving chromosomes 7 and 21. This genetic abnormality leads to a duplication of chromosome 7p, causing developmental delays and distinct physical features associated with 7p duplication syndrome.
Area of Science:
- Genetics
- Clinical Medicine
- Cytogenetics
Background:
- Genetic translocations can lead to unbalanced karyotypes, resulting in partial duplications or deletions of chromosomal material.
- 7p duplication syndrome is a rare genetic disorder characterized by intellectual disability and specific facial dysmorphisms.
Observation:
- A 1-year-old boy presented with global developmental delay, intellectual disability, and distinctive facial features including ocular hypertelorism, a low nasal bridge, and a small mandible.
- Cytogenetic analysis revealed an unbalanced karyotype (46,XY,add(21)(q22.3)) resulting from a maternal balanced translocation between chromosomes 7 and 21.
- Fluorescence in situ hybridization (FISH) confirmed the additional material on chromosome 21q originated from chromosome 7, specifically identifying an unbalanced translocation der(21)t(7;21)(p21.2;q22.3)mat.
Findings:
- The patient's karyotype indicated a duplication of the distal region of chromosome 7p.
- The observed phenotype in the patient closely resembles previously reported cases of 7p duplication syndrome.
- The findings suggest that the critical region responsible for the characteristic features of 7p duplication syndrome is located at 7p21.2 or a more proximal segment.
Implications:
- This case contributes to the understanding of the genotype-phenotype correlation in 7p duplication syndrome.
- Identifying the critical segment at 7p21.2 provides valuable information for genetic counseling and diagnosis of similar cases.
- Further research into the specific genes within the 7p21.2 region may elucidate the molecular mechanisms underlying the syndrome's features.
Abstract:
We describe a 1-year-old boy with mental and physical retardation, a large anterior fontanel, brachycephaly with flat occiput, short and stubby fingers, generalized hypotonia, ocular hypertelorism, low-nasal bridge, long philtrum, high-narrow palate, apparently low-set ears, and a small mandible. Cytogenetic analysis utilizing high resolution chromosome banding technique showed an unbalanced karyotype consisting of 46,XY,add(21)(q22.3) that originated from maternal balanced translocation between chromosomes 7 and 21. Fluorescence in situ hybridization (FISH) using micro-dissected library probe pool from chromosome 7 confirmed the additional material on 21q was derived from chromosome 7. Our results indicated that the patient had an unbalanced translocation, 46,XY, der(21)t(7;21)(p21.2;q22.3)mat, which resulted in duplication for distal 7p. Our patient is similar to reported cases with a 7p15-->pter or larger duplication of 7p, suggesting that the critical segment causing the characteristic phenotype of 7p duplication syndrome, including large anterior fontanel, exists at 7p21.2 or 7p21.2-->pter.