Uniparental isodisomy for paternal 7p and maternal 7q in a child with growth retardation

Area of Science:

• Genetics
• Human Molecular Genetics
• Reproductive Biology

Background:

• Uniparental isodisomy, where both homologous chromosomes come from one parent, is rare.
• Isochromosomes involve the presence of two identical arms (p and q) of a chromosome.
• This case involves simultaneous isochromosomes of both 7p and 7q arms, replacing normal homologues.

Purpose of the Study:

• To investigate a rare case of uniparental isodisomy in a growth-retarded infant.
• To determine the parental origin and extent of heterozygosity of the rearranged chromosomes.
• To explore potential mechanisms leading to the formation of chromosome 7 isochromosomes.

Main Methods:

• Cytogenetic analysis of the infant's chromosomes.
• Microsatellite marker analysis of the proband and parents to trace allele origins.
• Comparison of phenotypic features with previously reported cases.

Main Results:

• The infant presented with simultaneous isochromosomes of 7p and 7q, replacing normal chromosome 7 homologues.
• Microsatellite analysis confirmed paternal origin of 7p alleles and maternal origin of 7q alleles.
• The infant exhibited homozygosity for all analyzed chromosome 7 loci.

Conclusions:

• The findings suggest a potential mechanism involving incomplete mitotic interchange and sister-chromatid reunion in early zygotic division.
• The observed phenotype, including short stature and growth retardation, aligns with maternal isodisomy 7, highlighting the importance of paternal gene contribution from 7q.