View source for WBR0117

{{WBRQuestion
|QuestionAuthor=William J Gibson (Reviewed by {{YD}} and {{Rim}})
|ExamType=USMLE Step 1
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Gastrointestinal
|Prompt=A married couple with strong positive family history for cystic fibrosis undergo genetic testing. While neither the man nor his wife has cystic fibrosis, genetic tests reveal that both are carriers for the ΔF508 mutation. The couple refuses in vitro fertilization (IVF) in favor of a natural pregnancy. Which of the following is the most likely perinatal complication if the couple’s child has cystic fibrosis? 
|Explanation=Cystic fibrosis is an autosomal recessive genetic disease that is most commonly caused by a defective CFTR stemming from a deletion of phenylalanine residue at positive 508. Cystic fibrosis results in abnormal chloride transport due to a non-functional chloride channel, termed "cystic fibrosis transmembrane conductance regulator" (CFTR). Normally, the apical sodium channels reabsorb sodium across the ductular lumen. This phenomenon is followed the reabsorption of chloride counter-ion using CFTR. Patients with cystic fibrosis have abnormal CFTR that limits the amount of sodium and chloride that can be reabsorbed. As such, the hallmark of cystic fibrosis is sweat with high concentrations of salt.

Patients with cystic fibrosis suffer from symptoms caused by mucosal obstruction of the exocrine glands. Thick secretions in the lungs block the narrow distal airways and submucosal glands cause the formation of neutrophil-dominant mucopurulent debris with peribronchiolar inflammation, glandular hyperplasia, and scar tissue. In the pancreas, mucus accumulation and obstruction result from a reduced flushing capacity of the pancreatic ducts due to failure to release anions across the cellular membranes. Similarly in the intestines, abnormal chloride secretion leads to hyperviscous secretions leading to intestinal obstruction. Thus, 10-15% of neonates born with cystic fibrosis present with meconium ileus, characterized by the patient's failure to pass the first stool within the first 48 hours. Intestinal obstruction is usually followed by abdominal distention and bilious vomiting. In addition, rectal prolapse, which is protrusion of the internal rectal membranes, also occurs in as many as 10% of children with CF; it is caused by increased fecal volume, malnutrition, and increased intra–abdominal pressure.

|AnswerA=Blue baby syndrome
|AnswerAExp=Neonates with tetralogy of Fallot often present with blue baby syndrome. 
|AnswerB=Neonatal meningitis
|AnswerBExp=Patients with cystic fibrosis are not at a particular increased risk of neonatal meningitis, which is usually caused by ''Streptococcus agalactiae'' (Group B Streptococcus or GBS), ''E. coli'', and ''Listeria monocytogenes''.
|AnswerC=Vomiting
|AnswerCExp=[[Meconium ileus]] refers to the failure of a neonate to pass its first stool within 48 hours. It is caused by an obstruction of the ileum. The stool becomes a black-green thickened mass which may cause [[abdominal distension]] and [[bilious vomiting]] soon after birth. 
|AnswerD=Double bubble sign on chest x-ray
|AnswerDExp=Double bubble sign on chest x-ray is a radiographic sign of duodenal atresia, a common complication among newborns with [[Down syndrome]].
|AnswerE=White pupillary reflex during ophthalmologic examination
|AnswerEExp=Patients with retinoblastoma have leukocoria, a white pupillary reflex. Normal babies have a red pupillary reflex. 
|EducationalObjectives=Cystic fibrosis is associated with meconium ileus in newborns, characterized by failure to pass stools within the first 48 hours, intestinal distention, and bilious vomiting.
|References=Muller F, Aubry MC, Gasser B, Duchatel F, Boué J, Boué A. Prenatal diagnosis of cystic fibrosis. II. Meconium ileus in affected fetuses. Prenat Diagn. 1985;5(2):109-17<br>
Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med. 2005;352:1992-2001<br>
First Aid 2014 page 357
|RightAnswer=C
|WBRKeyword=Cystic fibrosis, CF, Meconium ileus, Bilious vomiting, Vomiting, Intestinal obstruction, Obstruction, Neonate, Newborn, Genetic, Genetics, Complication, Chloride, Channel, CFTR, Autosomal, Recessive, Autosomal recessive 
|Approved=No
}}