Chromosomal breakpoints characterization of two supernumerary ring chromosomes 20.

Area of Science:

• Genetics
• Cytogenetics
• Human Genetics

Background:

• Ring chromosome 20 (r(20)) is a rare chromosomal abnormality.
• No consistent phenotype has been established for r(20).

Observation:

• Two new cases of supernumerary r(20) were diagnosed prenatally.
• Patient 1 exhibited intrauterine growth retardation and craniofacial dysmorphism.
• Patient 2 presented with obesity and a normal phenotype.

Findings:

• Molecular cytogenetic characterization revealed distinct breakpoints and sizes for the two r(20) cases.
• Breakpoints were identified at 20p11.23/20q11.23 (13.6 Mb) for Patient 1 and 20p11.21/20q11.21 (4.8 Mb) for Patient 2.
• A review of 13 reported cases showed variable phenotypic abnormalities.

Implications:

• Precise characterization of chromosomal breakpoints in supernumerary r(20) is essential for establishing genotype-phenotype correlations.
• This detailed characterization aids in predicting the natural history and outcomes of r(20), particularly for prenatal diagnoses.
• Further research is needed to fully understand the spectrum of phenotypes associated with r(20).