USMLE Step 2 CK Lecture Notes 2019: Obstetrics/Gynecology (Kaplan Test Prep)

OB TRIAD

Autosomal   Recessive

Each affected individual has an affected parent (unless this is a new mutation).
Affected individuals will transmit the disease to 50% of their offspring.
Unaffected individuals will bear unaffected children (if penetrance is complete).
There are no carrier states.

Autosomal dominant examples include the following:

Polydactyly Marfan  syndrome Neurofibromatosis

Huntington  chorea Myotonic dystrophy Osteogenesis  imperfecta

Achondroplasia Polycystic   kidneys

Autosomal recessive

Transmission occurs equally to males and females, but the disease often skips
generations. Enzyme deficiencies are most common findings. Age of onset is
usually earlier with consistency in clinical expression. Carrier states are
common.

Transmitted by  both    sexes

Often   skips   generations

Male    and female  carriers

If  both    parents are heterozygous    for the gene,   25% of  offspring   will    be

affected,   50% will    be  carriers,   and 25% will    be  normal.