A 36-year-old nulligravid woman comes to the clinic for preconception counseling due to advanced maternal age. The patient has epilepsy that is well controlled on several antiepileptic medications. Her husband has no medical conditions. Temperature is 37.2 C (99 F), blood pressure is 128/76 mm Hg, pulse is 90/min, and respirations are 16/min. Examination shows a yellow-brown plaque with irregular borders measuring about 6 cm in diameter along the lower back. There are a few periungual fibromas on the hands and feet. Assume that the patient is heterozygous for her underlying disorder and that the couple will give birth to a boy. Which of the following is the likelihood that the boy will have this disorder?

Question

A 36-year-old nulligravid woman comes to the clinic for preconception counseling due to advanced maternal age.  The patient has epilepsy that is well controlled on several antiepileptic medications.  Her husband has no medical conditions.  Temperature is 37.2 C (99 F), blood pressure is 128/76 mm Hg, pulse is 90/min, and respirations are 16/min.  Examination shows a yellow-brown plaque with irregular borders measuring about 6 cm in diameter along the lower back.  There are a few periungual fibromas on the hands and feet.  Assume that the patient is heterozygous for her underlying disorder and that the couple will give birth to a boy.  Which of the following is the likelihood that the boy will have this disorder?

Quizplus · Accepted Answer

11ec25c8_da8d_41c5_bc81_9133d477c0bc_MD0003_00 This woman has epilepsy and skin findings concerning for tuberous sclerosis complex (TSC), a neurocutaneous disorder. Classic dermatologic manifestations include ash-leaf spots (hypopigmented macules), periungual fibromas (flesh-colored papules adjacent to the nail fold), malar angiofibromas, and a shagreen patch (orange peel-like plaque typically on the lower back). Most patients also have seizures and benign tumors in multiple organs (eg, skin, brain, kidney). The diagnosis is often clinical but can be confirmed by genetic testing. angiofibromas TSC is caused by a mutation in the TSC1 or TSC2 gene; the mutation can occur de novo or may be inherited through autosomal dominant transmission. With autosomal dominant disorders, a child needs to inherit only one copy of the mutant allele to be affected, and males and females are affected equally. In this case, one parent is heterozygous for the condition (ie, one mutant allele) and the other is healthy; therefore, the child of this couple has a 50% chance of inheriting the disorder (regardless of whether the child is a boy or a girl). However, clinical features vary within family members, so the severity of disease cannot be predicted. autosomal dominant (Choice A) If neither parent has a mutant allele, the child has no chance of inheriting the disorder; however, this woman has characteristic features of TSC. (Choice B) The likelihood that 2 carriers of an autosomal recessive disorder will have a boy who is affected is 12.5% (likelihood of having a boy × likelihood of disease = 0.5 × 0.25). autosomal recessive (Choice C) Assuming the sex of the child is unknown, the likelihood of this couple having a boy with TSC is 25% (likelihood of having a boy × likelihood of disease = 0.5 × 0.5). This case presumes that the child is a boy, making the likelihood of disease 50%. (Choice E) A child with a parent who is homozygous for TSC has a 100% chance of having the disorder. A son has a 100% chance of inheriting an X-linked recessive disorder in which the mother is affected and the father is healthy. X-linked recessive disorder Educational objective: Tuberous sclerosis complex is a neurocutaneous disorder that causes seizures, characteristic skin findings (eg, shagreen patches, periungual fibromas), and benign tumors of various organs (eg, skin, brain, kidney). Inheritance is autosomal dominant; therefore, males and females are equally affected. References: Tuberous sclerosis complex: review based on new diagnostic criteria. (http://www.ncbi.nlm.nih.gov/pubmed/29924239)

A 36-Year-Old Nulligravid Woman Comes to the Clinic for Preconception