Review Question - QID 106512

This patient most likely has Patau syndrome (trisomy 13), which is most commonly caused by meiotic nondisjunction.

Trisomy 13 is a genetic abnormality that results in a specific constellation of symptoms, and can be diagnosed with ultrasound and amniocentesis. Often, children present with a still birth, or pass away soon after birth. The most common physical presentations include an omphalocele, rocker-bottom feet, holoprosencephaly, microcephaly, polydactyly (distinct from Edwards), microphthalmia, and cleft lip and palate. Patients that survive into childhood often develop significant motor and neurologic disability. In 99% of cases, the disorder is caused by a random meiotic nondisjunction event. In approximately 1% of cases, a parent can carry a balanced translocation that has the potential to be inherited by their offspring in an unbalanced fashion.

Incorrect Answers:
Answer 1: This inheritance pattern requires that two alleles of a single phenotype be inherited, in order for the phenotype to be present in the offspring.

Answer 3: These are disorders of a single gene or enzyme that result in the inability to fully carryout a specific biochemical pathway. This often results in the deleterious accumulation of precursor substances.

Answer 4: The amniotic band can become tangled around the fetus, resulting in a decrease in blood flow to the extremities and subsequent growth restriction.

Answer 5: Specific exposures in utero such as alcohol, phenytoin and lithium can result in a specific constellation of birth defects.

Bullet Summary:
Trisomy 13 (Patau syndrome) presents with cleft lip and palate, polydactyly, rocker-bottom feet, holoprosencephaly, PCKD, omphalocele or umbilical hernia, and is most likely due to maternal meiotic nondisjunction.