Hemophilia A (X-linked recessive)

Scenario

A genetic counselor documents a three-generation hemophilia A pedigree during a prenatal consultation. The X-linked recessive pattern — carrier females who show no symptoms but pass the mutated allele — must be clearly distinguished from affected males. NSGC standard notation is required for clinical records and insurance pre-authorization.

Annotation key

• carrier-x — female carrier of an X-linked recessive allele; rendered as a circle with a centre dot per NSGC convention
• affected — fully filled symbol; individual expresses the condition
• unaffected — open (unfilled) symbol; no clinical presentation
• proband — the index case who prompted clinical referral (not used here, but add proband to any individual)
• I-1 -- I-2 followed by indented children — defines a mating pair and their offspring

How to read

Generation I: unaffected father, carrier mother. Generation II: one affected son (II-1), one carrier daughter (II-2), two unaffected children. Generation III: carrier daughter II-2 married an unaffected man; they produced another affected son (III-1) and another carrier daughter (III-2) — demonstrating the classic X-linked skip-generation pattern where the trait disappears in daughters only to re-emerge in grandsons.