Small familial supernumerary ring chromosome 2: FISH characterization and genotype-phenotype correlation

Area of Science:

• Genetics
• Cytogenetics
• Medical Genetics

Background:

• Mosaicism for small supernumerary marker chromosomes (SMCs) can present with variable phenotypes.
• SMC(2) involving the pericentromeric region of chromosome 2 is rare, with limited genotype-phenotype correlation data.
• Understanding SMCs is crucial for genetic counseling, especially in prenatal diagnosis.

Purpose of the Study:

• To characterize a novel small supernumerary marker chromosome (SMC) derived from chromosome 2.
• To investigate the genetic basis of psychotic illness and mild mental retardation in a proband.
• To review and correlate existing cases of SMC(2) or proximal 2q trisomy to understand genotype-phenotype relationships.

Main Methods:

• Fluorescent in situ hybridization (FISH) was used to identify and characterize the small supernumerary marker chromosome (SMC).
• YAC (yeast artificial chromosome) probes were employed to determine the specific chromosomal region involved (proximal 2q).
• A literature review of previously reported cases of SMC(2) or proximal 2q trisomy was conducted.

Main Results:

• A mother and child were found to be mosaic for a small supernumerary marker chromosome (SMC).
• The marker chromosome was identified as originating from the pericentromeric region of chromosome 2, with involvement of proximal 2q.
• The proband presented with psychotic illness and mild mental retardation, while the mother showed only minor dysmorphisms.

Conclusions:

• This case highlights a rare instance of mosaicism for an SMC(2) with proximal 2q involvement.
• Genotype-phenotype correlations for rare chromosomal abnormalities like SMC(2) are essential for accurate diagnosis and prognosis.
• Further research into SMCs is needed to improve genetic counseling and management, particularly for prenatal cases.