American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

When scoring FISH for DiGeorge syndrome, what does a missing ARSA probe signal indicate?

1. Normal chromosomal arrangement

2. Duplication of the ARSA region

3. Deletion of the ARSA region

4. Presence of an extra chromosome

The correct answer is: Deletion of the ARSA region

A missing ARSA probe signal when scoring FISH for DiGeorge syndrome indicates a deletion of the ARSA region. In the context of DiGeorge syndrome, which is commonly associated with a deletion on chromosome 22 (22q11.2), the absence of the ARSA (Arylsulfatase A) probe suggests that the corresponding locus has been lost due to genomic deletion. This is significant because deletions in this region are typically responsible for the clinical manifestations of DiGeorge syndrome, including developmental delays, congenital heart defects, and immune deficiencies. Identifying a deletion at this locus helps confirm the diagnosis of the syndrome and supports further genetic counseling and management for affected individuals. The presence of the ARSA probe signal is crucial for assessing the integrity of this genomic region, and a missing signal strongly points to a loss of material rather than a normal arrangement or duplication.