Understanding Genomic Imprinting

Genomic imprinting is an epigenetic phenomenon where the expression of a gene is determined by its parental origin. Essentially, only one copy of the gene, either the one inherited from the mother or the one from the father, is expressed, while the other copy is silenced. This process involves modifications like DNA methylation that don't alter the DNA sequence itself.

Disruptions in genomic imprinting can lead to various genetic disorders. The question asks us to identify which of the listed syndromes are caused by this phenomenon. Let's analyze each syndrome:

Syndrome Analysis for Genomic Imprinting

• I. Rubinstein Taybi syndrome: This syndrome is primarily associated with mutations in the CREBBP gene (on chromosome 16) or the EP300 gene (on chromosome 22). While epigenetic factors might be involved in some complex cases, it's not typically classified as a disorder caused directly by genomic imprinting.
• II. Prader-Willi syndrome: This is a classic example of a genomic imprinting disorder. It occurs due to the loss or absence of function of specific genes on the paternal chromosome 15 (in the region 15q11-q13). The corresponding genes on the maternal chromosome 15 are normally silenced due to imprinting.
• III. Angelman syndrome: Similar to Prader-Willi syndrome, Angelman syndrome is also a well-established genomic imprinting disorder. It results from the loss or absence of function of the *UBE3A* gene on the maternal chromosome 15 (in the region 15q11-q13). The paternal copy of this gene is typically silenced by imprinting.
• IV. Edward syndrome: Commonly known as Trisomy 18, this condition is caused by the presence of an extra copy of chromosome 18. This is a chromosomal abnormality involving an abnormal number of chromosomes (aneuploidy) and is not related to genomic imprinting.

Identifying Syndromes Caused by Genomic Imprinting

Based on the analysis of the specific syndromes:

• Prader-Willi syndrome (II) arises from issues with paternal gene expression on chromosome 15 due to genomic imprinting.
• Angelman syndrome (III) arises from issues with maternal gene expression on chromosome 15 due to genomic imprinting.
• Rubinstein Taybi syndrome (I) and Edward syndrome (IV) are not primarily caused by genomic imprinting.

Therefore, the syndromes caused by genomic imprinting among the options provided are Prader-Willi syndrome and Angelman syndrome.