Protein intolerance with deficient transport of basic aminoacids. Another inborn error of metabolism

Lysinuric Protein Intolerance: Not Only a Disorder for Pediatric Nephrologists - Case Report

INTRODUCTION

Lysinuric protein intolerance (LPI) is a multisystemic inborn error of metabolism with a variable clinical expressivity that usually begins in childhood with growth failure and gastroenterological/neurological problems related to the altered urea cycle and, later, with complications involving the renal, pulmonary, and immunohematological systems.

CASE REPORT

We present the case of a 40-year-old woman suffering from chronic kidney disease in the context of a LPI, whose diagnosis was challenging because the signs of the disease were always blurred and the patient never manifested critical episodes typical of this multisystemic disease. In addition to renal disease, splenomegaly, thrombocytopenia, elevated lactate dehydrogenase (LDH), hyperferritinemia, and hypertriglyceridemia were also present. A thorough investigation of the patient's food preferences revealed her spontaneous aversion to protein-containing foods and excessive drowsiness during the occurrence of infectious episodes or on the rare occasions of excessive protein intake, although without ever coming to medical attention. These nuanced signs led us to suspect an impairment of the urea cycle and ultimately allowed us to narrow down the diagnosis to LPI through biochemical and genetic investigations.

CONCLUSION

Nephrologists should consider LPI in the differential diagnosis, whenever a patient presents with mixed proteinuria, tubular dysfunction, and/or chronic kidney disease of unknown origin. In these circumstances, we suggest looking for other signs such as growth failure, signs and symptoms ascribed to urea-cycle impairment, pulmonary involvement, hepatosplenomegaly, and laboratory alterations such as pancytopenia, hyperferritinemia, lipid abnormalities, and elevated LDH.

Whole lung lavage and GM-CSF use for pulmonary alveolar proteinosis in an infant with lysinuric protein intolerance: a case report

BACKGROUND

Lysinuric protein intolerance (LPI) is a multi-organ metabolic disorder characterized by the imbalance in absorption and excretion of cationic amino acids like lysine, ornithine and arginine. Infants with LPI typically present with recurrent vomiting, poor growth, interstitial lung disease or renal impairment. The early onset of pulmonary alveolar proteinosis (PAP) has been reported to be associated with a severe form of LPI. Treatment of PAP most commonly consists of whole-lung lavage (WLL) and in autoimmune PAP, granulocyte-macrophage colony stimulating factor (GM-CSF) administration. Nevertheless, GM-CSF therapy in LPI-associated PAP has not been scientifically justified.

CASE PRESENTATION

We describe the case of an 8-month-old infant presenting with respiratory failure due to LPI associated with PAP, who was twice treated with WLL; firstly, while on veno-venous ECMO assistance and then by the use of a selective bronchial blocker. After the two treatments with WLL, she was weaned from daytime respiratory support while on initially subcutaneous, then on inhaled GM-CSF therapy.

CONCLUSIONS

This case supports the notion that GM-CSF therapy might be of benefit in patients with LPI-associated PAP. Further studies are needed to clarify the exact mechanism of GM-CSF in patients with LPI-associated PAP.

Genetics of Primary Hemophagocytic Lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) constitutes a rare, potentially life-threatening hyperinflammatory immune dysregulation syndrome that can present with a variety of clinical signs and symptoms, including fever, hepatosplenomegaly, and abnormal laboratory and immunological findings such as cytopenias, hyperferritinemia, hypofibrinogenemia, hypertriglyceridemia, elevated blood levels of soluble CD25 (interleukin (IL)-2 receptor α-chain), or diminished natural killer (NK)-cell cytotoxicity (reviewed in detail in Chapter 11 of this book). While HLH can be triggered by an inciting event (e.g., infections), certain monogenic causes have been associated with a significantly elevated risk of development of HLH, or recurrence of HLH in patients who have recovered from their disease episode. These monogenic predisposition syndromes are variably referred to as "familial" (FHL) or "primary" HLH (henceforth referred to as "pHLH") and are the focus of this chapter. Conversely, secondary HLH (sHLH) often occurs in the absence of monogenic etiologies that are commonly associated with pHLH and can be triggered by infections, malignancies, or rheumatological diseases; these triggers and the genetics associated with sHLH are discussed in more detail in other chapters in this book.

Lysinuric protein intolerance exhibiting renal tubular acidosis/Fanconi syndrome in a Japanese woman

Lysinuric protein intolerance (LPI), caused by pathogenic variants of SLC7A7, is characterized by protein aversion, failure to thrive, hyperammonemia, and hepatomegaly. Recent studies have reported that LPI can cause multiple organ dysfunctions, including kidney disease, autoimmune deficiency, pulmonary alveolar proteinosis, and osteoporosis. We report the case of a 47-year-old Japanese woman who was initially diagnosed with renal tubular acidosis (RTA), Fanconi syndrome, and rickets. At the age of 3 years, she demonstrated a failure to thrive. Urinary amino acid analysis revealed elevated lysine and arginine levels, which were masked by pan-amino aciduria. She was subsequently diagnosed with rickets at 5 years of age and RTA/Fanconi syndrome at 15 years of age. She was continuously treated with supplementation of vitamin D3, phosphate, and bicarbonate. A renal biopsy at 18 years of age demonstrated diffuse proximal and distal tubular damage with endocytosis-lysosome pathway abnormalities. Distinctive symptoms of LPI, such as protein aversion and postprandial hyperammonemia were not observed throughout the patient's clinical course. The patient underwent a panel-based comprehensive genetic testing and was diagnosed with LPI. As the complications of LPI involve many organs, patients lacking distinctive symptoms may develop various diseases, including RTA/Fanconi syndrome. Our case indicates that proximal and distal tubular damages are notable findings in patients with LPI. The possibility of LPI should be carefully considered in the management of RTA/Fanconi syndrome and/or incomprehensible pathological tubular damage, even in the absence of distinctive symptoms; furthermore, a comprehensive genetic analysis is useful for diagnosing LPI.

Inborn errors of amino acid metabolism - from underlying pathophysiology to therapeutic advances

Amino acids are organic molecules that serve as basic substrates for protein synthesis and have additional key roles in a diverse array of cellular functions, including cell signaling, gene expression, energy production and molecular biosynthesis. Genetic defects in the synthesis, catabolism or transport of amino acids underlie a diverse class of diseases known as inborn errors of amino acid metabolism. Individually, these disorders are rare, but collectively, they represent an important group of potentially treatable disorders. In this Clinical Puzzle, we discuss the pathophysiology, clinical features and management of three disorders that showcase the diverse clinical presentations of disorders of amino acid metabolism: phenylketonuria, lysinuric protein intolerance and homocystinuria due to cystathionine β-synthase (CBS) deficiency. Understanding the biochemical perturbations caused by defects in amino acid metabolism will contribute to ongoing development of diagnostic and management strategies aimed at improving the morbidity and mortality associated with this diverse group of disorders.

Plasma calprotectin is extremely high in patients with lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder affecting the transport of cationic amino acids. Elevated plasma zinc concentrations have been described in patients with LPI. Calprotectin is a calcium- and zinc-binding protein, produced by polymorphonuclear leukocytes and monocytes. Both zinc and calprotectin have an important role in immune system. In this study, we describe plasma zinc and plasma calprotectin concentrations in Finnish LPI patients. Plasma calprotectin concentration was measured from 10 LPI patients using an enzyme-linked immunosorbent assay (ELISA) and it was remarkably high in all LPI patients (median: 622 338 μg/L) compared to that in healthy controls (608 μg/L). Plasma zinc concentration was measured by photometry and it was normal or only mildly elevated (median: 14.9 μmol/L). All the patients had decreased glomerular infiltration rate (median: 50 mL/min/1.73 m2). In conclusion, we observed extremely high plasma calprotectin concentration in patients with LPI. Mechanism of this phenomenon is unknown.

Improving a Rare Metabolic Disorder Through Kidney Transplantation: A Case Report of a Patient With Lysinuric Protein Intolerance

Lysinuric protein intolerance (LPI) is a rare metabolic disorder with reduced renal and intestinal reabsorption of ornithine, lysine, and arginine. It is due to variants in SLC7A7, the gene encoding y+L amino acid transporter 1 (y+LAT1), which lead to urea cycle defects with protein intolerance. Chronic kidney disease in lysinuric protein intolerance is common and can progress to kidney failure and initiation of kidney replacement therapy. Kidney transplantation could in theory improve urine levels and, consequently, plasma levels of these amino acids and therefore improve clinical symptoms, as well as protein intolerance, in patients with lysinuric protein intolerance. However, data on kidney transplantation in patients with lysinuric protein intolerance are limited, and up until now no data on clinical and biochemical improvement after kidney transplantation have been reported. In this case report we describe a rare case of kidney transplantation in a lysinuric protein intolerance patient with substantial improvement in protein tolerance; in plasma and urine levels of ornithine, lysine, and arginine; and in lysinuric protein intolerance symptoms.

The Finnish genetic heritage in 2022 – from diagnosis to translational research

Isolated populations have been valuable for the discovery of rare monogenic diseases and their causative genetic variants. Finnish disease heritage (FDH) is an example of a group of hereditary monogenic disorders caused by single major, usually autosomal-recessive, variants enriched in the population due to several past genetic drift events. Interestingly, distinct subpopulations have remained in Finland and have maintained their unique genetic repertoire. Thus, FDH diseases have persisted, facilitating vigorous research on the underlying molecular mechanisms and development of treatment options. This Review summarizes the current status of FDH, including the most recently discovered FDH disorders, and introduces a set of other recently identified diseases that share common features with the traditional FDH diseases. The Review also discusses a new era for population-based studies, which combine various forms of big data to identify novel genotype–phenotype associations behind more complex conditions, as exemplified here by the FinnGen project. In addition to the pathogenic variants with an unequivocal causative role in the disease phenotype, several risk alleles that correlate with certain phenotypic features have been identified among the Finns, further emphasizing the broad value of studying genetically isolated populations.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

Amino Acid Transport Defects in Human Inherited Metabolic Disorders

Amino acid transporters play very important roles in nutrient uptake, neurotransmitter recycling, protein synthesis, gene expression, cell redox balance, cell signaling, and regulation of cell volume. With regard to transporters that are closely connected to metabolism, amino acid transporter-associated diseases are linked to metabolic disorders, particularly when they involve different organs, cell types, or cell compartments. To date, 65 different human solute carrier (SLC) families and more than 400 transporter genes have been identified, including 11 that are known to include amino acid transporters. This review intends to summarize and update all the conditions in which a strong association has been found between an amino acid transporter and an inherited metabolic disorder. Many of these inherited disorders have been identified in recent years. In this work, the physiological functions of amino acid transporters will be described by the inherited diseases that arise from transporter impairment. The pathogenesis, clinical phenotype, laboratory findings, diagnosis, genetics, and treatment of these disorders are also briefly described. Appropriate clinical and diagnostic characterization of the underlying molecular defect may give patients the opportunity to avail themselves of appropriate therapeutic options in the future.

Inducible Slc7a7 Knockout Mouse Model Recapitulates Lysinuric Protein Intolerance Disease

Lysinuric protein intolerance (LPI) is a rare autosomal disease caused by defective cationic amino acid (CAA) transport due to mutations in SLC7A7, which encodes for the y⁺LAT1 transporter. LPI patients suffer from a wide variety of symptoms, which range from failure to thrive, hyperammonemia, and nephropathy to pulmonar alveolar proteinosis (PAP), a potentially life-threatening complication. Hyperammonemia is currently prevented by citrulline supplementation. However, the full impact of this treatment is not completely understood. In contrast, there is no defined therapy for the multiple reported complications of LPI, including PAP, for which bronchoalveolar lavages do not prevent progression of the disease. The lack of a viable LPI model prompted us to generate a tamoxifen-inducible Slc7a7 knockout mouse (Slc7a7^-/-). The Slc7a7^-/- model resembles the human LPI phenotype, including malabsorption and impaired reabsorption of CAA, hypoargininemia and hyperammonemia. Interestingly, the Slc7a7^-/- mice also develops PAP and neurological impairment. We observed that citrulline treatment improves the metabolic derangement and survival. On the basis of our findings, the Slc7a7^-/- model emerges as a promising tool to further study the complexity of LPI, including its immune-like complications, and to design evidence-based therapies to halt its progression.

Proximal renal tubular acidosis with and without Fanconi syndrome

Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO₃⁻) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO₃⁻ wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO₃⁻ not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO₃⁻ reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO₃⁻, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaP_i-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.

Amino Acid Transport Across the Mammalian Intestine

The small intestine mediates the absorption of amino acids after ingestion of protein and sustains the supply of amino acids to all tissues. The small intestine is an important contributor to plasma amino acid homeostasis, while amino acid transport in the large intestine is more relevant for bacterial metabolites and fluid secretion. A number of rare inherited disorders have contributed to the identification of amino acid transporters in epithelial cells of the small intestine, in particular cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, and dicarboxylic aminoaciduria. These are most readily detected by analysis of urine amino acids, but typically also affect intestinal transport. The genes underlying these disorders have all been identified. The remaining transporters were identified through molecular cloning techniques to the extent that a comprehensive portrait of functional cooperation among transporters of intestinal epithelial cells is now available for both the basolateral and apical membranes. Mouse models of most intestinal transporters illustrate their contribution to amino acid homeostasis and systemic physiology. Intestinal amino acid transport activities can vary between species, but these can now be explained as differences of amino acid transporter distribution along the intestine. © 2019 American Physiological Society. Compr Physiol 9:343-373, 2019.

Abnormal coagulation and enhanced fibrinolysis due to lysinuric protein intolerance associates with bleeds and renal impairment

INTRODUCTION

Lysinuric protein intolerance (LPI), a rare autosomal recessive transport disorder of cationic amino acids lysine, arginine and ornithine, affects intestines, lungs, liver and kidneys. LPI patients may display potentially life-threatening bleeding events, which are poorly understood.

AIMS

To characterize alterations in haemostatic and fibrinolytic variables associated with LPI.

METHODS

We enrolled 15 adult patients (8 female) and assessed the clinical ISTH/SSC-BAT bleeding score (BS). A variety of metabolic and coagulation assays, including fibrin generation test derivatives, clotting time (CT) and clot lysis time (CLT), thromboelastometry (ROTEM), and PFA-100 and Calibrated Automated Thrombogram (CAT), were used.

RESULTS

All patients had mild-to-moderate renal insufficiency, and moderate bleeding tendency (BS 4) without spontaneous bleeds. Mild anaemia and thrombocytopenia occurred. Traditional clotting times were normal, but in contrast, CT in fibrin generation test, and especially ROTEM FIBTEM was abnormal. The patients showed impaired primary haemostasis in PFA, irrespective of normal von Willebrand factor activity, but together with lowered fibrinogen and FXIII. Thrombin generation (TG) was reduced in vitro, according to CAT-derived endogenous thrombin potential, but in vivo TG was enhanced in the form of circulating prothrombin fragment 1 and 2 values. Very high D-dimer and plasmin-α2-antiplasmin (PAP) complex levels coincided with shortened CLT in vitro.

CONCLUSIONS

Defective primary haemostasis, coagulopathy, fibrin abnormality (FIBTEM, CT and CLT), low TG in vitro and clearly augmented fibrinolysis (PAP and D-dimer) in vivo were all detected in LPI. Altered fibrin generation and hyperfibrinolysis were associated with the metabolic and renal defect, suggesting a pathogenetic link in LPI.

Renal involvement in lysinuric protein intolerance: contribution of pathology to assessment of heterogeneity of renal lesions

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disease caused by mutations in the SLC7A7 gene encoding the light subunit of a cationic amino acid transporter. Symptoms mimic primary urea cycle defects but dysimmune symptoms are also described. Renal involvement in LPI was first described in the 1980s. In 2007, it appeared that it could concern as much as 75% of LPI patients and could lead to end-stage renal disease. The most common feature is proximal tubular dysfunction and nephrocalcinosis but glomerular lesions are also reported. However, very little is known regarding histological lesions associated with LPI. We gathered every kidney biopsy of LPI-proven patients in our highly specialized pediatric and adult institution. Clinical, biological, and histological information was analyzed. Five LPI patients underwent kidney biopsy in our institution between 1986 and 2015. Clinically, 4/5 presented with proximal tubular dysfunction and 3/5 with nephrotic range proteinuria. Histology showed unspecific tubulointerstitial lesions and nephrocalcinosis in 3/5 biopsies and marked peritubular capillaritis in one child. Glomerular lesions were heterogeneous: lupus-like-full house membranoproliferative glomerulonephritis (MPGN) in one child evolved towards monotypic IgG1κ MPGN sensitive to immunomodulators. One patient presented with glomerular non-AA non-AL amyloidosis. Renal biopsy is particularly relevant in LPI presenting with glomerular symptoms for which variable histological lesions can be responsible, implying specific treatment and follow-up.

Update on Lysinuric Protein Intolerance, a Multi-faceted Disease Retrospective cohort analysis from birth to adulthood

Background

Lysinuric protein intolerance (LPI) is a rare metabolic disease resulting from recessive-inherited mutations in the SLC7A7 gene encoding the cationic amino-acids transporter subunit y⁺LAT1. The disease is characterised by protein-rich food intolerance with secondary urea cycle disorder, but symptoms are heterogeneous ranging from infiltrative lung disease, kidney failure to auto-immune complications. This retrospective study of all cases treated at Necker Hospital (Paris, France) since 1977 describes LPI in both children and adults in order to improve therapeutic management.

Results

Sixteen patients diagnosed with LPI (12 males, 4 females, from 9 families) were followed for a mean of 11.4 years (min-max: 0.4-37.0 years). Presenting signs were failure to thrive (n = 9), gastrointestinal disorders (n = 2), cytopenia (n = 6), hyperammonemia (n = 10) with acute encephalopathy (n = 4) or developmental disability (n = 3), and proteinuria (n = 1). During follow-up, 5 patients presented with acute hyperammonemia, and 8 presented with developmental disability. Kidney disease was observed in all patients: tubulopathy (11/11), proteinuria (4/16) and kidney failure (7/16), which was more common in older patients (mean age of onset 17.7 years, standard deviation 5.33 years), with heterogeneous patterns including a lupus nephritis. We noticed a case of myocardial infarction in a 34-year-old adult. Failure to thrive and signs of haemophagocytic-lymphohistiocytosis were almost constant. Recurrent acute pancreatitis occurred in 2 patients. Ten patients developed an early lung disease. Six died at the mean age of 4 years from pulmonary alveolar proteinosis. This pulmonary involvement was significantly associated with death. Age-adjusted plasma lysine concentrations at diagnosis showed a trend toward increased values in patients with a severe disease course and premature death (Wilcoxon p = 0.08; logrank, p = 0.17). Age at diagnosis was a borderline predictor of overall survival (logrank, p = 0.16).

Conclusions

As expected, early pulmonary involvement with alveolar proteinosis is frequent and severe, being associated with an increased risk of death. Kidney disease frequently occurs in older patients. Cardiovascular and pancreatic involvement has expanded the scope of complications. A borderline association between increased levels of plasma lysine and poorer outome is suggested. Greater efforts at prevention are warranted to optimise the long-term management in these patients.

Urine Beta2-Microglobulin Is an Early Marker of Renal Involvement in LPI

OBJECTIVE

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder affecting the transport of cationic amino acids. It has previously been shown that approximately one third of the Finnish LPI patients have impaired renal function. The aim of this study was to analyse in detail urine beta2-microglobulin values, renal dysfunction, oral L-citrulline doses and plasma citrulline concentrations in Finnish LPI patients.

METHODS AND RESULTS

Of the 41 Finnish LPI patients, 56% had proteinuria and 53% hematuria. Mean plasma creatinine concentration was elevated in 48%, serum cystatin C in 62%, and urine beta2-microglobulin in 90% of the patients. Seventeen per cent of the patients developed ESRD, and five of them received a kidney transplant. L-citrulline doses and fasting plasma citrulline concentrations were similar in adult LPI patients with decreased and normal GFR (mean ± SD 79.5 ± 29.2 vs. 82.4 ± 21.9 mg/kg/day, P = 0.619, and 80.3 ± 20.1 vs. 64.8 ± 23.0 μmol/l, P = 0.362, respectively).

CONCLUSIONS

Urine beta2-microglobulin is a sensitive early marker of renal involvement, and it should be monitored regularly in LPI patients. Weight-based oral L-citrulline doses and plasma citrulline concentrations were not associated with renal function. LPI patients with ESRD were successfully treated with dialysis and kidney transplantation.

Fanconi syndrome with lysinuric protein intolerance

We present the case of a 9-year-old child with lysinuric protein intolerance and Fanconi syndrome. She was referred to our hospital with a persistent metabolic acidosis and polyuria. Renal investigations revealed all laboratory signs of Fanconi syndrome, with glucosuria, generalized aminoaciduria, phosphaturia and severe hypercalciuria. The diagnosis of Fanconi syndrome was confirmed by a renal biopsy that showed extensive lesions of proximal tubular epithelial cells with vacuolation of these cells and a sloughing of the brush border.

The first Korean case of lysinuric protein intolerance: presented with short stature and increased somnolence

Lysinuric protein intolerance (LPI) is a rare inherited metabolic disease, caused by defective transport of dibasic amino acids. Failure to thrive, hepatosplenomegaly, hematological abnormalities, and hyperammonemic crisis are major clinical features. However, there has been no reported Korean patient with LPI as of yet. We recently encountered a 3.7-yr-old Korean girl with LPI and the diagnosis was confirmed by amino acid analyses and the SLC7A7 gene analysis. Her initial chief complaint was short stature below the 3rd percentile and increased somnolence for several months. Hepatosplenomegaly was noted, as were anemia, leukopenia, elevated levels of ferritin and lactate dehydrogenase, and hyperammonemia. Lysine, arginine, and ornithine levels were low in plasma and high in urine. The patient was a homozygote with a splicing site mutation of IVS4+1G > A in the SLC7A7. With the implementation of a low protein diet, sodium benzoate, citrulline and L-carnitine supplementation, anemia, hyperferritinemia, and hyperammonemia were improved, and normal growth velocity was observed.

First report of a molecular prenatal diagnosis in a tunisian family with lysinuric protein intolerance

Lysinuric protein intolerance (LPI, MIM# 222700) is an inherited aminoaciduria caused by defective transport of cationic amino acids (CAAs; arginine, lysine, ornithine) at the basolateral membrane of epithelial cells in the intestine and kidney. We report the first prenatal diagnosis by direct mutational analysis of LPI performed in a Tunisian family. An amniotic fluid sample was carried out at 16 weeks of gestation in a 32-year-old Tunisian woman who consulted for prenatal diagnosis. The 1471 delTTCT mutation at homozygous state was identified indicating that the fetus was affected by LPI. The identification of this specific mutation provides a tool, which can be easily applied in Tunisia for molecular diagnosis, genetic counseling, and prenatal diagnosis of LPI.

Growth hormone therapy is safe and effective in patients with lysinuric protein intolerance

BACKGROUND

Lysinuric protein intolerance (LPI) is an autosomal recessive cationic amino acid transport defect characterized by episodes of postprandial hyperammonemias and spontaneous protein aversion. Subnormal growth is common in spite of appropriate nutritional therapy. Growth hormone (GH) therapy promotes appetite, protein synthesis and accretion, but its possible growth-promoting effects and safety in patients with LPI are poorly known.

METHODS

Four LPI children aged 7-16 years were treated with GH for a period of 3-4.5 years. Dietary intakes and plasma amino acid levels were analyzed frequently in addition to routine monitoring of GH therapy.

RESULTS

Insulin-like growth factor-1 concentration was low and bone age was delayed in all LPI patients, but GH provocative test was pathological in only one of the patients. During the 3-4.5 years of GH therapy (dose 0.035-0.050 mg/kg/day), bone age did not catch up but height standard deviation score (SDS) improved by 0.7-1.8 SDS. There were no episodes of hyperammonemias.

CONCLUSIONS

Our data support safety and growth-promoting potential of long-term GH therapy in patients with LPI.

Lysinuric protein intolerance: reviewing concepts on a multisystem disease

Lysinuric protein intolerance (LPI) is an inherited aminoaciduria caused by defective cationic amino acid transport at the basolateral membrane of epithelial cells in intestine and kidney. LPI is caused by mutations in the SLC7A7 gene, which encodes the y(+)LAT-1 protein, the catalytic light chain subunit of a complex belonging to the heterodimeric amino acid transporter family. LPI was initially described in Finland, but has worldwide distribution. Typically, symptoms begin after weaning with refusal of feeding, vomiting, and consequent failure to thrive. Hepatosplenomegaly, hematological anomalies, neurological involvement, including hyperammonemic coma are recurrent clinical features. Two major complications, pulmonary alveolar proteinosis and renal disease are increasingly observed in LPI patients. There is extreme variability in the clinical presentation even within individual families, frequently leading to misdiagnosis or delayed diagnosis. This condition is diagnosed by urine amino acids, showing markedly elevated excretion of lysine and other dibasic amino acids despite low plasma levels of lysine, ornithine, and arginine. The biochemical diagnosis can be uncertain, requiring confirmation by DNA testing. So far, approximately 50 different mutations have been identified in the SLC7A7 gene in a group of 142 patients from 110 independent families. No genotype-phenotype correlation could be established. Therapy requires a low protein diet, low-dose citrulline supplementation, nitrogen-scavenging compounds to prevent hyperammonemia, lysine, and carnitine supplements. Supportive therapy is available for most complications with bronchoalveolar lavage being necessary for alveolar proteinosis.

Combined hyperlipidemia in patients with lysinuric protein intolerance

BACKGROUND AND AIMS

Lysinuric protein intolerance (LPI) is an autosomal recessive disorder characterized by defective transport of cationic amino acids lysine, arginine, and ornithine. Low plasma concentrations of arginine and ornithine lead to impaired urea cycle function and, subsequently, decreased protein tolerance. Patients often develop natural aversion to protein-rich foods, which may predispose them to nutritional problems. The objective of this retrospective study was to investigate lipid values and efficacy of lipid-lowering therapy in patients with LPI.

METHODS AND RESULTS

Serum total and high-density-lipoprotein (HDL)-cholesterol and triglyceride concentrations were analyzed in 39 Finnish LPI patients (14 males) aged 3-64 years. Dietary intakes were analyzed from food records. Mean [standard deviation (SD)] serum and HDL-cholesterol and triglyceride concentrations were 7.16 (2.13) mmol/l, 1.21 (0.58) mmol/l, and 4.0 (2.4) mmol/l, respectively. Patients with renal dysfunction had marginally higher total cholesterol and significantly higher triglyceride concentration than patients without renal impairment. Twenty-two patients were started on 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (atorvastatin or simvastatin). After 6 months, serum cholesterol and triglyceride concentrations had decreased by 32% (p < 0.001), whereas HDL-cholesterol had increased by 13% (p = 0.016).

CONCLUSION

Serum cholesterol and triglyceride values are markedly elevated in LPI patients. Although the mechanism of combined hyperlipidemia remains unknown and is not explained by fat consumption, hyperlipidemia is clearly progressive with age, suggesting that starting statin therapy early is probably beneficial. Statins are well-tolerated and efficacious in LPI.

Amino acid transport across mammalian intestinal and renal epithelia

The transport of amino acids in kidney and intestine is critical for the supply of amino acids to all tissues and the homeostasis of plasma amino acid levels. This is illustrated by a number of inherited disorders affecting amino acid transport in epithelial cells, such as cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, dicarboxylic aminoaciduria, and some other less well-described disturbances of amino acid transport. The identification of most epithelial amino acid transporters over the past 15 years allows the definition of these disorders at the molecular level and provides a clear picture of the functional cooperation between transporters in the apical and basolateral membranes of mammalian epithelial cells. Transport of amino acids across the apical membrane not only makes use of sodium-dependent symporters, but also uses the proton-motive force and the gradient of other amino acids to efficiently absorb amino acids from the lumen. In the basolateral membrane, antiporters cooperate with facilitators to release amino acids without depleting cells of valuable nutrients. With very few exceptions, individual amino acids are transported by more than one transporter, providing backup capacity for absorption in the case of mutational inactivation of a transport system.

Aminoacidurias: Clinical and molecular aspects

Inherited aminoacidurias are caused by defective amino-acid transport through renal (reabsorption) and in many cases also small intestinal epithelia (absorption). Recently, many of the genes causing this abnormal transport have been molecularly identified. In this review, we summarize the latest findings in the clinical and molecular aspects concerning the principal aminoacidurias, cystinuria, lysinuric protein intolerance, Hartnup disorder, iminoglycinuria, and dicarboxylic aminoaciduria. Signs, symptoms, diagnosis, treatment, causative or candidate genes, functional characterization of the encoded transporters, and animal models are discussed.

First reported case of lysinuric protein intolerance (LPI) in Lithuania, confirmed biochemically and by DNA analysis

We report on an 18-year-old Lithuanian girl with hepatosplenomegaly noticed at birth, which progressed thereafter. The patient had to wait about 17 years for an accurate diagnosis and appropriate therapy. Lactase deficiency, congenital cataract of the right eye, and osteoporosis were observed. Episodes of drowsiness were caused by intake of high-protein food. Laboratory findings included slight hyperammonaemia, high plasma Citr, Ala, Gly, Glu, Ser levels, as well as citrullinuria, lysinuria, glutaminuria, alaninuria, argininuria, prolinuria, hydroxyprolinuria, ornithinuria, and orotic aciduria. Aversion to high-protein diet strongly suggested a disorder resulting in hyperammonaemia. Citrullinaemia was suspected. Subsequently the diagnosis of LPI was made on the basis of biochemical and clinical features. Molecular genetic testing revealed a mutation in the SLC7A7 gene, confirming the diagnosis.

Nutrient intake in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder characterized by defective transport of cationic amino acids. Poor intestinal absorption and increased renal loss of arginine, ornithine and lysine lead to low plasma concentrations of these amino acids and, subsequently, to impaired urea cycle function. The patients therefore have decreased nitrogen tolerance, which may lead to hyperammonaemia after ingestion of normal amounts of dietary protein. As a protective mechanism, most patients develop strong aversion to protein-rich foods early in life. Oral supplementation with citrulline, which is absorbed normally and metabolized to arginine and ornithine, improves protein tolerance to some extent, as do sodium benzoate and sodium phenylbutyrate also used by some patients. Despite effective prevention of hyperammonaemia, the patients still consume a very restricted diet, which may be deficient in energy, essential amino acids and some vitamins and minerals. To investigate the potential nutritional problems of patients with lysinuric protein intolerance, 77 three- to four-day food records of 28 Finnish LPI patients aged 1.5-61 years were analysed. The data suggest that the patients are clearly at risk for many nutritional deficiencies, which may contribute to their symptoms. Their diet is highly deficient in calcium, vitamin D, iron and zinc. Individualized nutritional supplementation accompanied by regular monitoring of dietary intake is therefore an essential part of the treatment of LPI.

Nephropathy advancing to end-stage renal disease: a novel complication of lysinuric protein intolerance

OBJECTIVE

To analyze systemically the prevalence of renal involvement in a cohort of Finnish patients with lysinuric protein intolerance (LPI) and to describe the course and outcome of end-stage renal disease in 4 patients.

STUDY DESIGN

The clinical information in a cohort of 39 Finnish patients with LPI was analyzed retrospectively.

RESULTS

Proteinuria was observed in 74% of the patients and hematuria was observed in 38% of the patients during follow-up. Elevated blood pressure was diagnosed in 36% of the patients. Mean serum creatinine concentration increased in 38% of the patients, and cystatin C concentration increased in 59% of the patients. Four patients required dialysis, and severe anemia with poor response to erythropoietin and iron supplementation also developed in these patients.

CONCLUSIONS

Our findings suggest that renal function of patients with LPI needs to be carefully monitored, and hypertension and hyperlipidemia should be treated effectively. Special attention also should be paid to the prevention of osteoporosis and carnitine deficiency in the patients with end-stage renal disease associated with LPI. The primary disease does not prohibit treatment by dialysis and renal transplantation.

Successful whole lung lavage in pulmonary alveolar proteinosis secondary to lysinuric protein intolerance: a case report

BACKGROUND

Pulmonary alveolar proteinosis (PAP) is a rare disease characterised by accumulation of lipoproteinaceous material within alveoli, occurring in three clinically distinct forms: congenital, acquired and secondary. Among the latter, lysinuric protein intolerance (LPI) is a rare genetic disorder caused by defective transport of cationic amino acids. Whole Lung Lavage (WLL) is currently the gold standard therapy for severe cases of PAP.

CASE PRESENTATION

We describe the case of an Italian boy affected by LPI who, by the age of 10, developed digital clubbing and, by the age of 16, a mild restrictive functional impairment associated with a high-resolution computed tomography (HRCT) pattern consistent with pulmonary alveolar proteinosis. After careful assessment, he underwent WLL.

CONCLUSION

Two years after WLL, the patient has no clinical, radiological or functional evidence of pulmonary disease recurrence, thus suggesting that WLL may be helpful in the treatment of PAP secondary to LPI.

Hazards associated with pregnancies and deliveries in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an autosomal recessive transport disorder of the dibasic amino acids. The defect leads to deficiency of lysine, arginine, and ornithine and, secondarily, to a functional disorder of the urea cycle. Transient postprandial hyperammonemia and subsequent persistent protein aversion, linked with several other biochemical and clinical characteristics of the disease, suggest an increased risk for maternal and fetal complications during pregnancy and delivery. Our unique material on the outcomes of 18 pregnancies of 9 Finnish mothers with LPI and the follow-up of their 19 children shows that maternal LPI is truly associated with increased risk of anemia, toxemia, and intrauterine growth retardation during pregnancy and bleeding complications during delivery. Successful pregnancies and deliveries can still be achieved with careful follow-up of blood pressure and laboratory values. The children of the mothers with LPI generally develop normally. Special care of maternal protein nutrition and control of ammonemia, anemia, and toxemia during pregnancy are essential. We propose centralization of deliveries to obstetric units with capability to deal with bleeding complications and rare inborn errors of metabolism.

The Genetics of Heteromeric Amino Acid Transporters

Heteromeric amino acid transporters (HATs) are composed of a heavy ( SLC3 family) and a light ( SLC7 family) subunit. Mutations in system b0,+(rBAT-b0,+AT) and in system y+L (4F2hc-y+LAT1) cause the primary inherited aminoacidurias (PIAs) cystinuria and lysinuric protein intolerance, respectively. Recent developments [including the identification of the first Hartnup disorder gene (B0AT1; SLC6A19)] and knockout mouse models have begun to reveal the basis of renal and intestinal reabsorption of amino acids in mammals.

Lysinuric protein intolerance: mechanisms of pathophysiology

Heteromeric amino acid transporters (HATs) are composed of two subunits, a polytopic membrane protein (the light subunit) and a disulfide-linked type II membrane glycoprotein (the heavy subunit). HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y(+)L isoforms, asc, xc-, and b(0,+)). The light subunits confer the amino acid transport specificity to the HAT. Two transporters of this family are relevant for inherited aminoacidurias. Mutations in any of the two genes coding for the subunits of system b(0,+) (rBAT and b(0,+)AT) lead to cystinuria (MIM 220100). Transport defects in a system y(+)L isoform, composed of 4F2hc and y(+)LAT-1, result in lysinuric protein intolerance (LPI) (MIM 222700). In this case, only mutations in the light subunit y(+)LAT-1, but not in the heavy chain 4F2hc, cause the disease. LPI, in addition to affecting intestinal and renal reabsorption of amino acids, is a multisystemic disease affecting the urea cycle and presents also with symptoms related to the immune system. The pathogenesis of these alterations is less well, or not understood at all.

The Finnish Disease Heritage III: the individual diseases

This article is the third and last in a series entitled The Finnish Disease Heritage I-III. All the 36 rare hereditary diseases belonging to this entity are described for clinical and molecular genetic purposes, based on the Finnish experience gathered over a period of half a century. In addition, five other diseases are mentioned. They may be included in the list of the "Finnish diseases" after adequate complementary studies.

[Hematologic manifestations of inborn errors of metabolism]

Haematological symptoms can be helpful for the diagnosis of metabolic diseases. A megaloblastic anemia orientates to folate and cobalamine anomalies when associated with homocystinemia and decreased plasma methionine levels, or to congenital oroticuria (hypochromia), Pearson syndrome (sideroblasts and vacuolisation of precursors) and thiamine transporter abnormality (sideroblasts) in the absence of homocystinuria. An hemolytic anemia orientates to anomalies of anaerobic glycolysis, heme synthesis, or iron metabolism, and Wilson disease. A pancytopenia orientates to organic aciduria, lysinuric protein intolerance, mevalonic aciduria and lysosomal storage diseases (Gaucher, Niemann Pick, Wolman) when hepatosplenomegaly is present. Uremic hemolytic syndrome and hemophagocytic lymphohistiocytosis respectively orientate to B12 anomalies, lysinuric protein intolerance, lysosomal storage diseases and organic aciduria.

Molecular biology of mammalian plasma membrane amino acid transporters

Molecular biology entered the field of mammalian amino acid transporters in 1990-1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene (rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x(c)- and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.

Varicella and varicella immunity in patients with lysinuric protein intolerance

Two patients with lysinuric protein intolerance (LPI) had near-fatal generalized varicella infection with severe interstitial pneumonitis, hepatitis, decreased platelet count, bleeding and hypoalbuminaemia. Active haemolysis resulted in anaemia and massive haemoglobinuria. Serum lactate dehydrogenase activity and ferritin concentration, which in patients with LPI in normal circumstances exceed the upper reference values 3-folds to 10-fold, increased to > 10,000 U/L and > 10,000 micrograms/L, respectively. The patients were treated with fresh frozen plasma, red-cell transfusions and intravenous acyclovir for 14 days, and recovered clinically in a month. Retrospectively, 3 of the 32 other known Finnish patients with LPI had had varicella infection that had been more severe than that in the other children in the family or in subjects in the neighbourhood and had led to hospital admission. Varicella antibodies were measured in 24 patients; 5 had no antibodies and 5 had very low antibody titres. Primary vaccination of three patients with living varicella vaccine increased antibody titres measurably in one patient. We suggest that patients with LPI who have no varicella zoster antibodies should be treated with acyclovir if exposed to varicella and should be (re)vaccinated against chickenpox.

Lysinuric protein intolerance (LPI) gene maps to the long arm of chromosome 14

Lysinuric protein intolerance (LPI) is an autosomal recessive disease characterized by defective transport of cationic amino acids and by hyperammonemia. Linkage analysis in 20 Finnish LPI families assigned the LPI gene locus to the proximal long arm of chromosome 14. Recombinations placed the locus between framework markers D14S72 and MYH7, a 10-cM interval in which the markers D14S742, D14S50, D14S283, and TCRA showed no recombinations with the phenotype. The phenotype was in highly significant linkage disequilibrium with markers D14S50, D14S283, and TCRA. The strongest allelic association obtained with marker TCRA, resulting in a P(excess) value of .98, suggests that the LPI gene locus lies in close proximity to this marker, probably within a distance of < 100 kb.

Diagnostic applications of chromatography and capillary electrophoresis

Capillary electrophoresis (CE) equipped with a diode-array detector, and GC-MS have been used to determine diagnostic metabolites occurring in urine of patients with various metabolic disorders. The urine samples were injected directly onto the CE instrument without any pretreatment. GC-MS required extraction and derivatisation before separation. Identification of abnormal metabolites was based on migration times and characteristic diode-array spectra, or mass spectral library search when GC-MS was used. The CE method has previously been shown capable of diagnosing several metabolic diseases, and was now used on more difficult cases. CE readily diagnosed glyceric aciduria and the secondary metabolite in lysinuric protein intolerance, orotic acid. Methylmalonic aciduria required pressure elution in addition to high voltage to accomplish diagnosis. In mevalonic aciduria the characteristic metabolite had weak light absorption and the mevalonate peak also co-eluted with endogenous aromatic acids making diagnosis difficult. Both in the latter case and with the disorders glutaric aciduria I and glyceroluria, GC-MS was the method of choice. A possible role of CE in the routine system for diagnosing metabolic disorders, might be to use this method for pre-testing all urine samples. Samples with abnormal CE-profiles would subsequently be given high priority for more elaborate analysis with GC-MS and amino acid analyzer. In a different project a CE instrument designed for serum protein analysis was used to study sera from patients with myelomatosis. The method also allowed identification of the various immunoglobulins using immunosubtraction. Samples collected after diagnosis as well as many years prior to disease were available through the Janus-bank. This large serum bank comprises samples collected since 1973 at intervals from nearly 300000 blood donors. It was found that the monoclonal immunoglobulins characteristic of the disease started to appear in serum up to 15 years before clinical diagnosis.

Immunological abnormality in patients with lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a rare hereditary disorder manifesting hyperammonemia induced by low levels of basic amino acids, these low levels being due to the impaired transport of these acids in the intestinal mucosa and the renal tubules. Low serum arginine levels and probably the consequently low in vivo levels of nitric oxide (NO), which against acts as a physiological and immunological mediator/modulator, are thought to influence the immunological status in patients with LPI. Accordingly, this study was conducted to. We found that patients with LPI had leukocytopenia, high serum IgG levels, a high ratio of CD44B4-positive lymphocytes (helper inducer) to CD42H4-positive lymphocytes (suppressor inducer), low levels of leukocyte phagocytic, cytotoxic, and natural killer cell activity, and increased spontaneous proliferation of lymphocytes. These results were probably the consequence of persistent low NO levels in vivo.

Pulmonary manifestations in lysinuric protein intolerance

STUDY OBJECTIVES

To evaluate the pulmonary manifestations and the course of acute respiratory insufficiency associated with lysinuric protein intolerance (LPI).

DESIGN

Retrospective review of clinical data and chest radiographs (total 225) obtained during the lifetime follow-up of 31 LPI patients. About half of the 25 patients without respiratory symptoms underwent high-resolution computed tomography (HRCT) of the lungs, radionuclide perfusion imaging, whole body plethysmography, and diffusing capacity measurements.

PATIENTS

Thirty-one Finnish patients with LPI.

RESULTS

During the follow-up period, four children with LPI died in respiratory insufficiency, 1 adult had an episode of respiratory insufficiency, and another had chronic symptoms, whereas 25 patients remained symptom-free. The radiologic findings in acute progressive respiratory insufficiency were uniform: at first, reticulonodular interstitial densities and, later on, progressive airspace disease. At autopsy, three patients showed pulmonary alveolar proteinosis and one had pulmonary hemorrhage and cholesterol granulomas. One adult had reversible respiratory insufficiency with signs of bronchiolitis obliterans, another adult had recurrent episodes of chest pain, dyspnea, and hypoxia. Of the symptom-free patients, one third (8 of 25) had signs suggestive of pulmonary fibrosis evidenced on chest radiographs and two thirds (8 of 14) had signs evidenced by HRCT films. Most symptom-free patients showed mild abnormalities either in perfusion imaging (9 of 12) or in function tests (8 of 12).

CONCLUSION

In childhood, patients with LPI are highly predisposed to develop pulmonary hemorrhages and alveolar proteinosis. Interstitial lung densities may precede the acute phase. Most adult LPI patients show radiologic signs of interstitial lung disease but only a few show clinical impairment.

Lysinuric protein intolerance with chronic interstitial lung disease and pulmonary cholesterol granulomas at onset

Hyperammonemia and encephalopathy developed in an 11-year-old girl with chronic interstitial lung disease and cholesterol casts in her lung biopsy specimen. She had decreased plasma levels of ornithine, lysine, and arginine and excessive urinary excretion of lysine and arginine, consistent with the diagnosis of lysinuric protein intolerance. Analysis of plasma and urinary amino acids should be considered in the diagnostic evaluation of patients with interstitial lung disease of uncertain origin.

Carbamoylphosphate synthetase deficiency in an adult: deterioration due to administration of valproic acid

A 24-year-old patient had symptoms of lethargy, convulsions and hyperammonaemia during valproic acid therapy. Cessation of valproic acid treatment brought about an improvement both of the symptoms and of the hyperammonaemia. However, enzymatic analysis after the cessation of valproic acid therapy revealed a complete absence of carbamoylphosphate synthetase (CPS) activity in liver biopsy. A unique polypeptide band, corresponding to the control CPS protein in molecular weight ('CPS-like' protein), was found in normal amounts in the patient's liver on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. This CPS-like protein seemed to be more labile than the control, because the polypeptide band became faint after freeze-thawing. Intravenous administration of L-alanine resulted in a significant increase of serum urea and a transient increase of blood ammonia concentrations. These results strongly suggest that the patient has a labile CPS protein with no activity in vitro but some activity in vivo. We consider that valproic acid may have disrupted some metabolic adaptation by reducing N-acetylglutamate in the liver, which in combination with CPS deficiency induced severe hyperammonaemia.

The human cationic amino acid transporter (ATRC1): Physical and genetic mapping to 13q12–q14

The product of the mouse Rec-1 locus is an integral membrane protein that determines susceptibility to infection by murine ecotropic retroviruses. Recently it has been determined that its role in normal cell metabolism is transport of the cationic amino acids, arginine, lysine, and ornithine across the plasma membrane. Southern blot analysis of genomic DNA from a panel of 48 mouse-human somatic cell hybrids assigned the human version of this gene, ATRC1, to chromosome 13. Chromosomal in situ hybridization localized the gene to 13q12-q14. A restriction fragment length polymorphism (RFLP) was detected with TaqI. There were two alleles with frequencies of 0.29 and 0.71. Pairwise linkage analysis established linkage between ATRC1 and ATP1AL1, D13S1, D13S6, D13S10, D13S11, D13S21, D13S22, D13S33, D13S36, and D13S37. Multilocus linkage analysis of five of the loci indicated that the most likely order of loci in this region was D13S11-ATP1AL1-ATRC1-D13S6-D13S33.

Advances in the use of computerized gas chromatography-mass spectrometry and high-performance liquid chromatography with rapid scanning detection for clinical diagnosis

A multi-component analytical system designed for the diagnosis of metabolic disorders is described. The urinary components are separated by a variety of chromatographic techniques, including automated amino acid analysis, high-performance liquid chromatography with diode-array detection and gas chromatography-mass spectrometry with a computerized mass spectral library search for identification of organic acids. The complete system can be used to diagnose over 100 different metabolic diseases. The usefulness of the chromatographic system is exemplified by the pre- and postnatal diagnosis of glutaric aciduria type I, the diagnosis of lysinuric protein intolerance and of alkaptonuria. Drugs and diet may cause interfering metabolites, as exemplified by glycofurol, used as a solvent for intravenous drugs, and saccharin. It is predicted that chromatography and mass spectrometry will continue to be important diagnostic tools for many years ahead.

Familial lysinuric protein intolerance presenting as coma in two adult siblings

Lysinuric protein intolerance (LPI) is an inborn error of metabolism which usually presents in infancy with failure to thrive and vomiting. Two patients are described who presented in adult life with hyperammonaemic coma due to LPI. Both had been underweight and had had intermittent gastrointestinal symptoms during childhood. They were of normal intellect and had maintained good health, until presentation in their thirties, by unconscious dietary protein avoidance. The diagnosis of LPI should be considered in patients who present with obscure relapsing coma associated with hyperammonaemia. Considerable clinical improvement may result from dietary protein restriction and citrulline supplementation.