How are LGMDs subclassified by inheritance?

• A. LGMD type 1 is autosomal dominant and LGMD type 2 is X-linked
• B. LGMDs are classified by age of onset only
• C. LGMD type 1 is autosomal recessive and LGMD type 2 is autosomal dominant
• D. LGMD type 1 (autosomal dominant) and LGMD type 2 (autosomal recessive)

Answer: (D)

Inheritance pattern is used to categorize LGMDs in this scheme. LGMD type 1 corresponds to autosomal dominant forms, while LGMD type 2 corresponds to autosomal recessive forms. This reflects how the mutated genes are passed down and the associated recurrence risks: dominant forms can appear with a single mutant copy, giving about a 50% chance of passing the condition to offspring; recessive forms require two mutated copies, with a higher likelihood for carriers in the family and a 25% risk for each child if both parents are carriers. There are other LGMD forms, such as X-linked types, but those are classified separately and not part of this type 1/type 2 framework. So labeling type 1 as autosomal dominant and type 2 as autosomal recessive accurately describes this inheritance-based subdivision.