The following is a diagram that presents a pedigree of a family affected by Danon disease, a condition that causes a malfunction of the heart. Filled circles and squares represent affected individuals, while open circles and squares represent phenotypically unaffected individuals.
What is most likely true about the disease-causing allele?

It is X-linked dominant.
It is X-linked recessive.
It is autosomal dominant.
It is autosomal recessive.