Antenatal Hyperechogenic Colon and Cystinuria.

A male newborn was investigated for history of antenatal hyperechogenic colon (HEC) detected at 32 weeks of gestation. In the first week of life, urinary ultrasonography showed nephrolithiasis. Urinary amino acid analysis expressed increased excretion of dibasic amino acids, and high urinary cystine levels were detected in both spot and 24-hour urine specimens. He was diagnosed as cystinuria, and genetic analysis of the patient revealed a heterozygous mutation in SLC7A9 gene. Antenatal presentation of cystinuria with HEC is rare and reported to be associated with a more severe disease course.

Non-contrast computed tomography characteristics in a large cohort of cystinuria patients.

PURPOSE: Cystine stones are widely considered hard and difficult to treat. Hounsfield Units (HU) are used in other stone types to estimate 'hardness' and treatments based on that finding. Our objective was to report mean HU of cystine stones in vivo in a large case series of cystinuria patients and assess for differences in genotype. METHODS: A prospective case series of cystinuria patients referred to a specialist centre was analysed. CT imaging was assessed by two independent radiologists to determine in vivo attenuation of cystine calculi. Mean HU was compared for both cystinuria genes (SLC3A1 and SLC7A9) using an independent t-test. RESULTS: 164 adult cystinuric patients were identified (55% male), median age 43 years (range 18-80). Median follow up was 31 months (IQR 10-62). Genetic data available for 153/164 (93%) demonstrated 97 SLC3A1 (63%) and 55 (36%) SLC7A9 mutations (39 homozygous, 16 heterozygous) and one heterozygous for both SLC3A1/SLC7A9. 107 patients had CT images available demonstrating calculi. Median HU across the cohort was 633 (5th to 95th centile 328-780). There was no difference in mean HU between SLC3A1 and SLC7A9 genotypes (p = 0.68) or homo and heterozygous SLC7A9 (p = 0.70). Mean HU correlated with stone size (Pearson correlation coefficient = 0.51, p < 0.001). CONCLUSION: In this large single centre cystinuria cohort, mean HU was low for stones that are difficult to treat. Calculi of < 800 HU should prompt consideration of a cystinuria diagnosis. Attenuation was not associated with genotype, and distinct 'smooth' and 'rough' stones were not observed. Calculi with HU > 1000 are unlikely pure cystine, and in a known cystinuric would suggest conversion to another stone type.

Metabolic consequences of cystinuria.

BACKGROUND: Cystinuria is an inherited disorder of renal amino acid transport that causes recurrent nephrolithiasis and significant morbidity in humans. It has an incidence of 1 in 7000 worldwide making it one of the most common genetic disorders in man. We phenotypically characterized a mouse model of cystinuria type A resultant from knockout of Slc3a1. METHODS: Knockout of Slc3a1 at RNA and protein levels was evaluated using real-time quantitative PCR and immunofluorescence. Slc3a1 knockout mice were placed on normal or breeder chow diets and evaluated for cystine stone formation over time suing x-ray analysis, and the development of kidney injury by measuring injury biomarkers. Kidney injury was also evaluated via histologic analysis. Amino acid levels were measured in the blood of mice using high performance liquid chromatography. Liver glutathione levels were measured using a luminescent-based assay. RESULTS: We confirmed knockout of Slc3a1 at the RNA level, while Slc7a9 RNA representing the co-transporter was preserved. As expected, we observed bladder stone formation in Slc3a1-/- mice. Male Slc3a1-/- mice exhibited lower weights compared to Slc3a1+/+. Slc3a1-/- mice on a regular diet demonstrated elevated blood urea nitrogen (BUN) without elevation of serum creatinine. However, placing the knockout animals on a breeder chow diet, containing a higher cystine concentration, resulted in the development of elevation of both BUN and creatinine indicative of more severe chronic kidney disease. Histological examination revealed that these dietary effects resulted in worsened kidney tubular obstruction and interstitial inflammation as well as worsened bladder inflammation. Cystine is a precursor for the antioxidant molecule glutathione, so we evaluated glutathione levels in the livers of Slc3a1-/- mice. We found significantly lowered levels of both reduced and total glutathione in the knockout animals. CONCLUSIONS: Our results suggest that that diet can affect the development and progression of chronic kidney disease in an animal model of cystinuria, which may have important implications for patients with this disease. Additionally, reduced glutathione may predispose those with cystinuria to injury caused by oxidative stress. Word count: 327.

Spectrum of mutations in cystinuria patients presenting with prenatal hyperechoic colon.

Cystinuria is a heterogeneous, rare but important cause of inherited kidney stone disease due to mutations in 2 genes: SLC3A1 and SLC7A9. Antenatal hyperechoic colon (HEC) has been reported in some patients as a non-pathological consequence of the intestinal transport defect. We report 83 patients affected by cystinuria: 44 presented prenatally with a HEC (HEC group) and 39 with a classical postnatal form (CC group). SLC3A1 and SLC7A9 were sequenced. All patients were fully genotyped, and the relationship between the genotype and clinical features was analyzed. We identified mutations in SLC3A1 in 80% of the HEC group and in only 49% of the CC group. The SLC3A1 p.Thr216Met mutation was found in 21% of the alleles in the HEC group but was never found in the CC group. Most of the mutations found in the HEC group were considered severe mutations in contrast with the CC group. Twenty-five novel mutations were reported. This study shows a relationship between genotype and the clinical form of cystinuria, suggesting that only the patients with the most severe mutations presented with an HEC. These results emphasized the need for prenatal cystinuria screening using classical third-trimester ultrasound scan and the early management of suspected newborns.

Isolated hyperechoic fetal colon before 36 weeks' gestation reveals cystinuria.

OBJECTIVES: To determine whether there is an association between the fetal ultrasound finding of hyperechoic colon and the gestational age at which it presents and cystinuria. METHODS: A prospective national survey was performed in France including all observations of isolated fetal hyperechoic colon detected at routine second- and third-trimester ultrasound over a 2-year period. Collected images were reviewed by experts. Colon was defined as being hyperechoic when its echogenicity was at least equal to that of the iliac bone. It was diagnosed when large tubular echogenic portions of the colon, without a focal mass and without posterior acoustic shadows, were observed at the periphery of the abdomen. Urinary amino acid analysis was performed after birth in the cases identified to test for cystinuria. RESULTS: Nineteen fetuses with ultrasound findings of hyperechoic colon were included, and the mothers of 16 of these agreed to participate in the study. In eight of nine cases of hyperechoic colon observed before 36 weeks' gestation cystinuria was confirmed at birth. In the seven remaining cases, observed after 36 weeks, none was found to have cystinuria and all had normal images at previous routine ultrasound scans at 22 and 33 weeks. When present, no difference in the sonographic appearance of hyperechoic colon was noted between the two groups. In the cystinuria-affected cases, the length of the hyperechoic mass appeared to increase with gestational age. CONCLUSIONS: In our experience, the presence of a hyperechoic colon at routine ultrasound scan before 36 weeks' gestation should prompt screening for cystinuria at birth, while later observation (> 36 weeks) of this finding does not appear to be related to any disease.

Studies on renal function in patients with cystinuria.

Total and separate renal functions were evaluated in 40 patients with cystinuria. The average duration of the renal stone disease was 26 years (range 1-53). The patients had been subjected to a stone-preventing regimen composed of increased fluid intake, urinary alkalinization and treatment with a sulphydryl compound, tiopronin or D-penicillamine, for an average of 11.7 years (range 1-24). Urinary cystine concentration was determined regularly to monitor the treatment. All patients were examined with gamma camera renography and an assessment of glomerular filtration rate (GFR), and early and late renographic results could be compared in 30 patients. The early renographic evaluation showed that 43% of binephric patients (13/30) had an abnormal relative renal function (RRF) before the start of the stone-preventing treatment. At the late evaluation, 50% of binephric patients (17/34) had an abnormal RRF, while 30% of all patients (12/40) had a GFR below the age-related normal range. Thirty percent of 74 evaluated kidneys (22/74) had a separate GFR below an estimated age-related normal range. At the late evaluation only 30% of the patients had functionally unaffected kidneys with both normal GFR and bilateral normal renography. There was, however, no case with terminal renal failure. The separate GFR of kidneys with a history of staghorn stones was significantly lower than for kidneys without that special type of stones, but otherwise there was no relationship between renal functional impairment and other estimates of the activity of the renal stone disease. In conclusion, impairment of renal function is common in patients with stone-forming cystinuria. Stone-preventive treatment appears to be effective in preserving renal function. The high frequency of renal functional impairment justifies close surveillance of this group of patients. By renographic examination, unilateral changes in renal function can be detected at an early stage and patients at risk for further deterioration of renal function can be identified.

Cystine calculi are radiopaque.

Cystine calculi are said to be either radiolucent or radiopaque. In the past, contamination of the calculi with calcium has been given as the reason for a radiopaque appearance. However, most cystine stones are pure cystine and contain essentially no calcium. When compared to adjacent fluids and tissues, they are radiopaque because of their higher physical density and their higher effective atomic number.

Cystinuria: a surgical challenge.

A case is reported in which cystinuria was unresponsive to medical treatment. Replacement of both ureters with small intestine gave a satisfactory result.