Which is the first step in the testing strategy for imprinting disorders?

The first step in the testing strategy for imprinting disorders is methylation studies, which is why this option is the correct answer. Imprinting disorders are characterized by the differential expression of genes based on their parental origin, and they often involve alterations in the imprinting marks, specifically DNA methylation patterns.

Methylation studies help to determine whether the regulatory regions of imprinted genes are appropriately methylated, which can indicate an abnormality associated with specific imprinting disorders such as Prader-Willi syndrome or Angelman syndrome. These tests can identify whether there is an epigenetic alteration in the methylation status, which is crucial for diagnosing imprinting-related conditions.

In contrast, while deletion analysis through karyotype and chromosomal microarray analysis might be relevant for identifying structural genetic abnormalities, they are not specifically targeted for the imprinting changes that are central to these disorders. Whole gene sequencing is more comprehensive but does not address the epigenetic factors that are critical in imprinting disorders upfront. Therefore, this makes methylation studies the most appropriate initial step in assessing these conditions.