What is the correct modal number for a patient with Turner syndrome with an isochromosome Xq?

Turner syndrome is characterized by the presence of a single X chromosome in females, resulting in a total chromosomal count of 45 instead of the usual 46. However, in cases of Turner syndrome involving an isochromosome of the long arm of the X chromosome (Xq), the patient may have additional chromosomal material that can alter the total count.

In this scenario, an isochromosome Xq means that one of the X chromosomes has lost its short arm (Xp) and instead has two copies of the long arm (Xq). This leads to a chromosomal composition of 46 in total since the presence of the isochromosome adds another arm to the complement, balancing out the loss of the other X chromosome.

Therefore, when considering the modal number for a patient with Turner syndrome who has an isochromosome Xq, the correct modal number is 46. This total takes into account the additional genetic material contributed by the isochromosome, hence the correct answer reflects this balance.