Renal and intestinal hexose transport in familial glucose-galactose malabsorption

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Abstract
Glucose transport by jejunal mucosa in vitro and kidney in vivo was investigated in a 3 yr old patient with congenital glucose-galactose malabsorption, her family, and 16 normal volunteers. Glucose transport by normal human jejunal mucosa was concentrative, saturable, sodium and energy dependent, and exhibited competitive inhibition. Biopsy specimens from six normal controls and an asymptomatic 5 yr old brother of the proband accumulated glucose to concentrations 16 times that in the incubation medium. The proband's mucosa was unable to concentrate glucose throughout a 60 min incubation period. Both of her parents and a half sister demonstrated impaired glucose transport. Their values fell between normal and those of the proband. Influx of glucose was impaired but efflux of glucose from the mucosa of these three heterozygotes was identical with that in three normal controls. A kinetic analysis indicated a reduced capacity (Vmax), but a normal affinity (Km) for glucose transport by their intestinal mucosa. All subjects accumulated fructose similarly. Renal glucose transport was investigated using renal glucose titration techniques. A partial defect in renal glucose reabsorption was found in the proband. Her brother's titration curve was similar to that of seven normal volunteers. We conclude that familial glucose-galactose malabsorption is inherited as an autosomal recessive trait, that heterozygotes for this disorder are detectable and demonstrate a reduced capacity for glucose transport, and that absent intestinal glucose transport is accompanied by partial impairment of renal glucose transport.