Ontogeny of Amino Acid Reabsorption in Human Kidney. Evidence from the Homozygous Infant with Familial Renal Iminoglycinuria for Multiple Proline and Glycine Systems

Abstract

Summaryadditional transport process(es) in the renal tubule, perhaps one with a preference for iminoacids and another with preference for seven infants French Canadim9' Our J e~s h , glycine (16,24). Since net reabsorption is determined to a great and one Greek) with massive selective hyperiminoglycinuria (proline, hydroxyproline, and glycine) were detected by urine screening extent by brush border membrane transport activity of the proxiin the second week of life. Follow-up investigations and family ma1 tubule (19,20), in this instance a benign mutation appears to studies revealed that each subject had a benign condition, frmilial be a useful probe, revealing the presence of more than one renal iminoglycinuria, an autosomal recessive condition. transport system serving iminoacids and glycine in that membrane of tubular epithelial cells. In this report, we have used the occurThe family studies ( Table 1 and Fig. 1) indicate the presence of rence of ontogeny and mutation together to examine this possiat least two different mutant alleles segregating in this small group bility in the human infant. of probands. Homozygotes of two forms and one genetic compound were identified.Quantitative studies revealed normal concentrations of proline (Table 2). Frat-azi Jewish, and one Greek), each with exceptional iminoglycinuria, tional excretion (c&ccR) of both proline and glyche in the were discovered in the second week of life by the urine screening probands was far in excess of that expected for the noranal program of the Quebec Network of Genetic ~e d i c i n e (10, 25). postnatal infant; F E~ and F E~~~ 100% of the filtered After follow-up qualitative studies had confirmed the presence load on occasion (~i~. 4). A of maturing reab-of persistent massive iminoglycinuria, each infant was admitted, sorptive activity was apparent in the proband group. probe with informed consent, as a day patient to the Clinical Investigareabsorption earlier than glycine reabsorption in the tion Unit at the Montreal Children's Hospital. More than one homozygotes (and the genetic compound) as it does in the normal quantitative study was performed during the first year of life in infants (Fig. 5).five of the patients (the probands for pedigrees 1, 2, 3, 4, and 6) Our fmdmgs suggest that three gene products serve net tubular and repeat qualitative studies were possible in six (the aforemenreabsorption of imino acids and glycine in human kidney. one, tioned probands plus proband 5). Family studies confirmed the affected by mutation in our patients, is responsible for a shared hereditary nature of the condition in all seven probands. *ansport activity; a second with preference for proline, and not For quantitative studies, a timed morning urine wllection was by the mutation, has an schedule of postnatal obtained in the fasting state. Glucose-water (5% w/v) was offered maturation; and a third with preference for glyche, also not to increase the urine rate during the by the mutation, has a schedule of maturation. period which lasted about 3 hr. Ur...

Identification of Mammalian Proline Transporter SIT1 (SLC6A20) with Characteristics of Classical System Imino

“…Total RNA was isolated from rat tissues using TRIzol reagent (Invitrogen) according to the manufacturer's protocol. For reverse transcription, 0.5 g of oligo(dT) [12][13][14][15][16][17][18] and 1 l of dNTPs (10 mM) were added to 1 g of total RNA in a total volume of 10 l. The mixture was incubated for 10 min at 65°C and then chilled on ice. Dithiothreitol (2 l, 0.1 M), 10ϫ reverse transcriptase buffer (2 l), MgCl 2 (4 l, 25 mM), and 40 units of RNaseOUT (Invitrogen) were added, and the mixture was incubated at 42°C for 2 min.…”

“…Kidney-Newborn rodents and man exhibit a marked hyperexcretion of proline that disappears within a few days, 1 week, 1 month, or 3 months after birth in rat, dog, and man, respectively (13,44,45). Studies using rat renal brush-border membrane preparations suggested that the proline hyperexcretion results from depressed Na ϩ -dependent proline reuptake in the neonate (3,44,46).…”

“…Total kidney RNA was isolated from the mouse fetuses (embryonic days 16, 17, 18, and 19), neonates (days 1 and 3), and adult mice. discrete ontogenies (13). Accordingly, iminoglycinuria may result from more than one defect of renal tubule amino acid transporters.…”

“…Family studies revealed that heterozygous infants of certain probands exhibit only glycinuria, but not iminoglycinuria. Therefore, iminoglycinuria has been suggested to be caused by defects of two or more renal tubule amino acid transporters (13,14).…”

Iminoglycinuria and hyperglycinuria are discrete human phenotypes resulting from complex mutations in proline and glycine transporters

“…In the absence of controlled prospective studies of IG and HG cohorts, some of these associations may represent ascertainment bias. Based on detailed biochemical studies in 7 families, Lasley and Scriver (19) suggested that 3 genes account for imino acid and glycine reabsorption in the kidney proximal tubule, namely a common transporter for both types of amino acids and a specific transporter each for glycine and imino acids. This model of 1 common and 2 specific transporters is well supported by transport studies in intact tubules, brush-border membrane vesicles, and cell lines from a wide variety of organisms (20).…”