Routine Neonatal Testing Suggests That a Baby Lacks a Transport

Routine neonatal testing suggests that a baby lacks a transport protein responsible for the uptake of cysteine in the intestines and kidneys.However,although cysteine accumulates in the urine,its concentration in the plasma is normal when the child receives a diet containing protein.Which intestinal transporter probably provides for uptake of cysteine in this child?

A) CFTR
B) Na⁺/K⁺/2Cl^- cotransporter,isoform 1 (NKCC1)
C) Epithelial sodium channel (ENaC)
D) Peptide transporter 1 (PepT1)
E) SLC6A19 gene