[size=20px]Which of the following has been linked to VACTERL association?

 

A mutation in sonic hedgehog signaling

 

B RET proto-oncogene

 

C ΔF508 (delta F-508) gene mutation

 

D methylenetetrahydrofolatereductase (MTHFR) deficiency

 

E APC gene[/size]

A

A

correct

 

Sonic hedgehog (SHH) signaling coordinates precise temporal and spatial events during embryogenesis. The Gli zinc finger transcription factor is the key transducer of Hedgehog signaling within the cell. There are three Gli genes (Gli1, Gli2, and Gli3) in humans and mice which are located on different chromosomes. Gli mutant mice display a spectrum of defects that mimic the human VACTERL association.

 

These associated defects were initially described in 1973 by Quan and Smith as the VATER association with vertebral defects (V), anal atresia (A), tracheoesophageal fistula with esophageal atresia (TE), radial and renal dysplasia ®. Cardiac and limb abnormalities were added later (VACTERL). The association (i.e. a nonrandom coexistence of congenital anomalies more frequent than allowed by random chance) is present when two or more anomalies coexist; rarely are more than 3 simultaneously present. The incidence is about 1 in 5,000 live births and the etiology of the association is unknown but is felt to be multifactorial. The heritability is low suggesting a possible role for environmental disruptors of SHH signaling.

 

Metabolism of the amino acid homocysteine depends on a pathway involving the enzyme MTHFR. Patients who are heterozygous for the MTHFR binding site gene have normal levels of homocysteine, but homozygous defect may lead to excess homocysteine and a hypercoagulable state. It has not been linked to VACTERL.

 

RET is an abbreviation for "rearranged during transfection". The RET proto-oncogene on chromosome 10 encodes for a tyrosine kinase receptor (TRK) is associated with Hirschsprung disease and MEN 2 (multiple endocrine neoplasia). The RET gene makes proteins involved in the neural crest and nerve cell migration.

 

The delta-F508 mutation is the most common known genetic cause of cystic fibrosis. The gene product is also known as the cystic fibrosis transmembrane conductance regulator (CFTR). It functions in opening chloride channels in the respiratory epithelial cells. The abnormality is found in about 1 in 30 Caucasians in the US.

 

The APC gene is linked with familial polyposis.