Final answer:
Children with Down syndrome should be evaluated for atlantoaxial instability, a potentially serious condition affecting the neck, before engaging in certain sports to ensure safety. So, the correct answer is option c.
Step-by-step explanation:
A child diagnosed with Down syndrome should be evaluated for atlantoaxial instability before participating in some sports. This condition involves excessive movement at the junction between the atlas (C1) and axis (C2) vertebrae in the neck, which can lead to spinal cord injury in those with Down syndrome, especially in sports with the potential for impact or injury to the neck.
It is critical to obtain a medical evaluation, including possibly an x-ray, to check for this instability as part of the safety screening process prior to sports participation. While the other options listed (hyperflexibility, cutis marmorata, and Brushfield's spots) may be associated with Down syndrome, they do not typically require specific sports-related evaluations.