Distinct outcomes of chloride diarrhoea in two siblings with identical genetic background of the disease: implications for early diagnosis and treatment

The genetics of monogenic intestinal epithelial disorders

Monogenic intestinal epithelial disorders, also known as congenital diarrheas and enteropathies (CoDEs), are a group of rare diseases that result from mutations in genes that primarily affect intestinal epithelial cell function. Patients with CoDE disorders generally present with infantile-onset diarrhea and poor growth, and often require intensive fluid and nutritional management. CoDE disorders can be classified into several categories that relate to broad areas of epithelial function, structure, and development. The advent of accessible and low-cost genetic sequencing has accelerated discovery in the field with over 45 different genes now associated with CoDE disorders. Despite this increasing knowledge in the causal genetics of disease, the underlying cellular pathophysiology remains incompletely understood for many disorders. Consequently, clinical management options for CoDE disorders are currently limited and there is an urgent need for new and disorder-specific therapies. In this review, we provide a general overview of CoDE disorders, including a historical perspective of the field and relationship to other monogenic disorders of the intestine. We describe the genetics, clinical presentation, and known pathophysiology for specific disorders. Lastly, we describe the major challenges relating to CoDE disorders, briefly outline key areas that need further study, and provide a perspective on the future genetic and therapeutic landscape.

Congenital chloride diarrhea clinical features and management: a systematic review

INTRODUCTION

Congenital chloride diarrhea (CLD) is a rare autosomal recessive disorder characterized by watery diarrhea with a high level of fecal Cl^-, metabolic alkalosis, and electrolyte alterations. Several intestinal and extraintestinal complications and even death can occur. An optimal knowledge of the clinical features and best therapeutic strategies is mandatory for an effective management.

METHODS

Articles published between 1 January 1965 and 31 December 2019, reported in PUBMED and EMBASE, were evaluated for a systematic review analyzing four categories: anamnestic features, clinical features, management, and follow-up strategies.

RESULTS

Fifty-seven papers reporting information on 193 CLD patients were included. The most common anamnestic features were positive family anamnesis for chronic diarrhea (44.4%), consanguinity (75%), polyhydramnios (98.3%), preterm delivery (78.6%), and failure to pass meconium (60.7%). Mean age at diarrhea onset was 6.63 days. Median diagnostic delay was 60 days. Prenatal diagnosis, based on molecular analysis, was described in 40/172 (23.3%). All patients received NaCl/KCl-substitutive therapy. An improvement of diarrhea during adulthood was reported in 91.3% of cases. Failure to thrive (21.6%) and chronic kidney disease (17.7%) were the most common complications.

CONCLUSIONS

This analysis of a large population suggests the necessity of better strategies for the management of CLD. A close follow-up and a multidisciplinary approach is mandatory to manage this condition characterized by heterogeneous and multisystemic complications.

IMPACT

In this systematic review, we describe data regarding anamnestic features, clinical features, management, and follow-up of CLD patients obtained from the largest population of patients ever described to date. The results of our investigation could provide useful insights for the diagnostic approach and the management of this condition.

Suicide attempt using potassium tablets for congenital chloride diarrhea: A case report

BACKGROUND

Congenital chloride diarrhea (CCD) is a rare inherited disorder of intestinal electrolyte transport that results in a large wastage of electrolytes and water. Advances in substitution therapy using sodium chloride (NaCl) and potassium chloride (KCl) have dramatically improved survival for patients with CCD. Slow-release KCl is widely prescribed as a potassium supplement; however, it has also occasionally been used in suicide attempts, as potassium poisoning can generate life-threatening hyperkalemia.

CASE SUMMARY

A 26-year-old female presented to the emergency department (ED) with self-poisoning, having taken 30 tablets of slow-release KCl (total: 240 mmol potassium) following an auditory hallucination. The patient had been undergoing substitution therapy with NaCl and KCl for CCD and been followed up in the pediatric department. One month prior, she developed insomnia and anxiety and had consulted a psychiatrist. At the ED, although her general condition was good, she appeared agitated. Her serum potassium level was 7.0 mmol/L, indicating hyperkalemia, and electrocardiographic changes showed tenting of the T-waves. She responded to the administration of calcium gluconate, sodium bicarbonate, and insulin with glucose, and the serum potassium level improved. Finally, she was diagnosed with schizophrenia.

CONCLUSION

In CCD management, physicians should pay careful attention to patients’ extraintestinal issues, including psychological disorders that may emerge in adulthood.

Congenital chloride diarrhea and Pendred syndrome: case report of siblings with two rare recessive disorders of SLC26 family genes

BACKGROUND

Congenital chloride diarrhea (CLD; OMIM 214700) is a rare autosomal recessive disorder caused by pathogenic variations in the solute carrier family 26 member A3 (SLC26A3) gene. Without salt substitution, this chronic diarrheal disorder causes severe dehydration and electrolyte disturbances. Homozygous variants in the nearby gene SLC26A4 disrupt anion exchange in the inner ear and the thyroid, causing Pendred syndrome (PDS; OMIM 274600), which is the most frequent form of syndromic deafness.

CASE PRESENTATION

We report an unusual co-occurrence of two rare homozygous mutations in both the SLC26A3 and SLC26A4 genes, causing a rare combination of both CLD and PDS in two siblings. Although the clinical pictures were typical, the combined loss of these anion transporters might modulate the risk of renal injury associated with CLD.

CONCLUSIONS

Familial presentation of two rare autosomal recessive disorders with loss of function of different SLC26 anion transporters is described. Independent homozygous variants in the SLC26A3 and SLC26A4 genes cause CLD and PDS in siblings, shedding light on co-occurrence of rare recessive traits in the progeny of consanguineous couples.

Clinical Features, Molecular Genetics, and Long-Term Outcome in Congenital Chloride Diarrhea: A Nationwide Study in Japan

OBJECTIVE

To clarify clinical and genetic features of Japanese children with congenital chloride diarrhea (CCD).

STUDY DESIGN

This was a multi-institutional, retrospective survey of 616 pediatric centers in Japan with identified patients with CCD between 2014 and 2018. Mutations involving SLC26A3 were detected by Sanger sequencing.

RESULTS

Thirteen patients met all entry criteria including mutations in SLC26A3, and 14 patients satisfied clinical diagnostic criteria. Homozygous or compound heterozygous mutations in SLC26A3, including 6 novel mutations, were identified in 13 of these 14 patients (93%). The most common (detected in 7 of 13) was c.2063-1g>t. Median age at diagnosis was 1 day. Nine of the patients meeting all criteria were diagnosed as neonates (69%). Median follow-up duration was 10 years. When studied, 8 patients had <5 stools daily (62%), and all had fewer than in infancy. Only 1 patient had nephrocalcinosis, and 3 (23%) had mild chronic kidney disease. Neurodevelopment was generally good; only 1 patient required special education. Five patients (38%) received long-term sodium, potassium, and chloride supplementation.

CONCLUSIONS

Early fetal ultrasound diagnosis and prompt long-term sodium, potassium, and chloride supplementation were common management features. Genetic analysis of SLC26A3 provided definitive diagnosis of CCD. In contrast with previously reported localities, c.2063-1g>t might be a founder mutation in East Asia.

Congenital chloride losing diarrhea: A single center experience in a highly consanguineous population

Congenital chloride losing diarrhea (CCLD) is a rare type of chronic watery diarrhea due to mutations in SLC26A3 gene leading to defective chloride-bicarbonate exchanges with the resultant loss of chloride and retention of bicarbonate.We aim to define pediatric Saudi CCLD patients' characteristics to achieve prompt diagnosis, management, follow up with good quality of life, and prevention of complications in these patients.We carried retrospective data review of demographic, clinical, laboratory, radiographic, and outcome of all pediatric patients fulfilling the criteria of CCLD over 10 years from 2004 to 2014 from a single center in Taif region, Saudi Arabia.Forty-nine patients fulfilled the criteria of CCLD from 21 families with more than one affected patient in the same family in 90% of them and positive consanguinity in 91% of the cohort. Most patients were born preterm with intrauterine growth restriction and usually neonatal intensive care unit (NICU) admissions with prematurity and its complications. Thirteen patients were discharged without diagnosis of CCLD and 3 were misdiagnosed as intestinal obstruction with unnecessary surgical intervention. Many complications do existed with renal complications being the most common with three patients received renal transplantation.Prematurity with abdominal distension and stool like urine were the commonest presentation of CCLD in Saudi children. Positive consanguinity and more than one affected sibling are present in most of our cohort.High index of suspicion by clinicians is a cornerstone for early diagnosis with subsequent favorable outcome.A multicenter national incidence study of CCLD in KSA and its genetic attributes is recommended. Premarital screening should be implemented specially for consanguineous marriage.

Captopril in congenital chloride diarrhoea: a case study

An 11 months 22 days old girl presented with a history of watery diarrhoea since birth, failure to thrive, and developmental delay. Her diagnosis was congenital chloride diarrhoea (CCD) with raised level of chloride (>90 mmol/L) in stool in the absence of cystic fibrosis. Management of CCD included replacement of NaCl, KCl, and correction of dehydration. Diarrhoea of the patient was resolved with Captopril, which was initially provided to the patient for managing heart failure. To our knowledge, this is the first reported case of CCD that shows the beneficial effect of Captopril. Therefore, we suggest that further study is warranted as to the potential for Captopril as additional option in the treatment for CCD. We present this case report with the informed consent of the patient's guardian.

The SLC26 gene family of anion transporters and channels

The phylogenetically ancient SLC26 gene family encodes multifunctional anion exchangers and anion channels transporting a broad range of substrates, including Cl(-), HCO3(-), sulfate, oxalate, I(-), and formate. SLC26 polypeptides are characterized by N-terminal cytoplasmic domains, 10-14 hydrophobic transmembrane spans, and C-terminal cytoplasmic STAS domains, and appear to be homo-oligomeric. SLC26-related SulP proteins of marine bacteria likely transport HCO3(-) as part of oceanic carbon fixation. SulP genes present in antibiotic operons may provide sulfate for antibiotic biosynthetic pathways. SLC26-related Sultr proteins transport sulfate in unicellular eukaryotes and in plants. Mutations in three human SLC26 genes are associated with congenital or early onset Mendelian diseases: chondrodysplasias for SLC26A2, chloride diarrhea for SLC26A3, and deafness with enlargement of the vestibular aqueduct for SLC26A4. Additional disease phenotypes evident only in mouse knockout models include oxalate urolithiasis for Slc26a6 and Slc26a1, non-syndromic deafness for Slc26a5, gastric hypochlorhydria for Slc26a7 and Slc26a9, distal renal tubular acidosis for Slc26a7, and male infertility for Slc26a8. STAS domains are required for cell surface expression of SLC26 proteins, and contribute to regulation of the cystic fibrosis transmembrane regulator in complex, cell- and tissue-specific ways. The protein interactomes of SLC26 polypeptides are under active investigation.

Congenital chloride diarrhea in dizygotic twins

Congenital chloride diarrhea (CLD) is a rare inherited autosomal recessive disorder. Mutations of the solute carrier family 26 member 3 gene cause profuse, chloride ion rich diarrhea, which results in hypochloremia, hyponatremia and metabolic alkalosis with dehydration. If a fetal ultrasound shows bowel dilatation suggestive of bowel obstruction, or if a neonate shows persistent diarrhea and metabolic alkalosis, CLD should be considered in the differential diagnosis. The severity of CLD varies, but early detection and early therapy can prevent complications including growth failure. We report a case of dizygotic twins affected by CLD who had been born to non-consanguineous parents. Both of them showed growth failure, but one of the twins experienced worse clinical course. He showed developmental delay, along with dehydration and severe electrolyte imbalance. He was diagnosed with CLD first at 6-month age, and then the other one was also diagnosed with CLD.

Congenital chloride diarrhea in Korean children: novel mutations and genetic characteristics

Congenital chloride diarrhea (CLD, OMIM#214700) is an autosomal recessive disorder caused by mutations in the solute carrier family 26 member 3 (SLC26A3) gene, which encodes an intestinal chloride/bicarbonate exchanger. While more than 50 mutations have been identified throughout the world, there have been no data on the genetic characteristics of the patients of East Asian ethnic origin. In this study, we performed genetic analysis by direct sequencing of the 20 exons and parts of exon-intron boundaries of the SLC26A3 gene in eight patients of Korean origin with non-consanguineous parents. We identified three novel mutations, including two splice-site mutations (c.2063-1G>T in intron 18, c.1047+3 A>C in intron 12) and one missense mutation (p.Ser134Asn in exon 5). One previously identified mutation was also found (p.Pro131Leu in exon 5). The most common mutation was c.2063-1G>T, which was found in at least one allele of all patients.

CONCLUSION

This is the first report to demonstrate the genetic background of CLD in a single ethnic group of East Asian descent. The c.2063-1G>T mutation could be suggested as a founder mutation in Korean population so that the targeting sequencing for the mutation would be a cost-efficient screening method to confirm a diagnosis of CLD in patients of Korean descent.

Prenatal diagnosis and management of congenital chloride diarrhea: A case report of 2 siblings

Congenital chloride diarrhea (CLD) is a rare hereditary disease. The basic defect of CLD is massive loss of Cl(-) and fluid into the ileum and colon. Prenatal diagnosis of this disease is quite important because the infant requires electrolyte supplementation from the early postnatal period. Two cases in which prenatal diagnoses of CLD were made in siblings are reported. Extreme electrolyte imbalance may cause fetal cardiac dysfunction or a poor general condition leading to a non-reassuring fetal status in cases with CLD. Therefore, frequent fetal monitoring using cardiotocograms and ultrasound may be beneficial to some fetuses with CLD to detect fetal deterioration. In addition, repeated amnioreduction may be required to treat severe polyhydramnios and threatened preterm delivery.

Significance of molecular testing for congenital chloride diarrhea

OBJECTIVES

Autosomal recessive, congenital chloride diarrhea (CLD) is a form of persistent secretory diarrhea, presenting with polyhydramnios and intractable diarrhea from birth. CLD is caused by mutations in the SLC26A3 gene, encoding a Na+-independent Cl/HCO3- exchanger. The diagnosis is generally made on the basis of high fecal chloride concentration in patients with serum electrolyte homoeostasis corrected by salt substitution. We aimed to evaluate the role of diagnostic genetic testing in CLD.

PATIENTS AND METHODS

Clinical and laboratory data were collected from 8 unrelated children diagnosed as having or suspected to have CLD. The evaluation included physical examination, routine clinical chemistry, and SLC26A3 mutation analysis by direct sequencing of DNA extracted from buccal swabs or peripheral leukocytes.

RESULTS

CLD was initially diagnosed on high fecal chloride concentrations in 7 patients, and by mutation analysis in 1 patient. In 3 of these patients the correct diagnosis was made more than 6 months after birth. We identified SLC26A3 mutations on both alleles in all 8 patients with CLD, including 3 novel missense and 4 novel truncating mutations. We present a compilation of reported SLC26A3 mutations and polymorphisms.

CONCLUSIONS

The diagnosis and therapy of CLD were considerably delayed in 3 of 8 patients from this series, highlighting the potential of misdiagnosing CLD. We add 7 novel mutations, including 3 missense changes of highly conserved residues to a total of 41 mutations in this gene. Molecular analysis is efficient and should be considered as a means of early diagnosis of CLD, especially if the clinical diagnosis remains uncertain.

Congenital diarrheal disorders: improved understanding of gene defects is leading to advances in intestinal physiology and clinical management

Congenital diarrheal disorders (CDD, Online Mendelian Inheritance in Man [OMIM] 251850) represent one of the most challenging clinical conditions for pediatric gastroenterologists because of the severity of the clinical picture and the broad range of disorders in its differential diagnosis. The number of conditions included within CDD has gradually increased. Recent advances made in the pathophysiology of these conditions have led to a better understanding of the more common diarrheal diseases. Based on the body of data accumulated in recent years, we suggest that CDD be classified in 4 categories depending on the alteration in absorption and transport of nutrients and electrolytes, enterocyte differentiation and polarization, enteroendocrine cell differentiation, and modulation of the intestinal immune response. Our knowledge of the genes responsible for CDD is also rapidly increasing, thanks to linkage studies based on genome-wide analysis of polymorphisms. In this context, the identification of disease genes is a step forward in the diagnostic approach to a patient in whom CDD is strongly suspected. However, it is conceivable that faster, less expensive molecular procedures will, in the near future, become available. This approach could spare the patient invasive procedures and limit complications associated with a delay in diagnosis. Furthermore, carrier and prenatal molecular diagnosis may help pediatricians better manage the condition in the early stages of life.

Review article: the clinical management of congenital chloride diarrhoea

BACKGROUND

Congenital chloride diarrhoea in a newborn is a medical emergency, requiring early diagnostics and treatment to prevent severe dehydration and infant mortality. While most of the 250 cases reported arise from Finland, Poland and Arab countries, single cases with this autosomal recessive disorder appear worldwide. Such congenital chloride diarrhoea rarity makes diagnosis difficult. Life-long salt substitution with NaCl and KCl stabilizes fluid, electrolyte and acid-base balance diagnosis. When properly treated, the long-term outcome is favourable.

AIM

To summarize data on congenital chloride diarrhoea diagnosis, pathophysiology and treatment, and to provide guidelines for both acute and long-term management of congenital chloride diarrhoea.

METHODS

Data are based on MEDLINE search for 'chloride diarrhoea', in addition to clinical experience in the treatment of the largest known series of patients.

RESULTS

Treatment of congenital chloride diarrhoea involves (i) life-long salt substitution; (ii) management of acute dehydration and hypokalaemia during gastroenteritis or other infections; and (iii) recognition and treatment of other manifestations of the disease, such as intestinal inflammation, renal impairment and male subfertility.

CONCLUSIONS

This review summarizes data on congenital chloride diarrhoea and provides guidelines for treatment. After being a mostly paediatric problem, adult patients constitute a rare challenge for gastroenterologists worldwide.

Slc26a9 is inhibited by the R-region of the cystic fibrosis transmembrane conductance regulator via the STAS domain

SLC26 proteins function as anion exchangers, channels, and sensors. Previous cellular studies have shown that Slc26a3 and Slc26a6 interact with the R-region of the cystic fibrosis transmembrane conductance regulator (CFTR), (R)CFTR, via the Slc26-STAS (sulfate transporter anti-sigma) domain, resulting in mutual transport activation. We recently showed that Slc26a9 has both nCl(-)-HCO(3)(-) exchanger and Cl(-) channel function. In this study, we show that the purified STAS domain of Slc26a9 (a9STAS) binds purified (R)CFTR. When Slc26a9 and (R)CFTR fragments are co-expressed in Xenopus oocytes, both Slc26a9-mediated nCl(-)-HCO(3)(-) exchange and Cl(-) currents are almost fully inhibited. Deletion of the Slc26a9 STAS domain (a9-DeltaSTAS) virtually eliminated the Cl(-) currents with only a modest affect on nCl(-)-HCO(3)(-) exchange activity. Co-expression of a9-DeltaSTAS and the (R)CFTR fragment did not alter the residual a9-DeltaSTAS function. Replacing the Slc26a9 STAS domain with the Slc26a6 STAS domain (a6-a9-a6) does not change Slc26a9 function and is no longer inhibited by (R)CFTR. These data indicate that the Slc26a9-STAS domain, like other Slc26-STAS domains, binds CFTR in the R-region. However, unlike previously reported data, this binding interaction inhibits Slc26a9 ion transport activity. These results imply that Slc26-STAS domains may all interact with (R)CFTR but that the physiological outcome is specific to differing Slc26 proteins, allowing for dynamic and acute fine tuning of ion transport for various epithelia.

Congenital cataract and congenital chloride diarrhoea-a unique combination and antenatal diagnosis

Congenital chloride diarrhoea (CCD) is a serious inherited defect of intestinal electrolyte absorption transmitted in an autosomal recessive way. The molecular pathology involves an epithelial Cl(-)/HCO(3)(-) exchanger protein, encoded by the solute carrier family 26 member 3 gene (SLC26A3) and known DRA (down regulated in adenomas) in the distal ileum and colon. Polyhydramnios, premature birth, ileus without meconium passage, hypochloremia, and hyponatremia are typical features of CCD in the neonate followed by chronic metabolic alkalosis, hypokalemia, hypochloremia, retarded growth and renal impairment in older children and adults if the disease is not adequately treated. Antenatal diagnosis if made on the basis of findings on ultrasonography-a non-invasive diagnostic test-can help in early management of the disorder immediately after birth and, thus, prevent the sequelae. We present an interesting case of CCD diagnosed antenatally and found to have congenital cataract, which is a unique occurrence not reported in literature so far.

A case of congenital chloride diarrhea: information obtained through long-term follow-up with reduced electrolyte substitution

Congenital chloride diarrhea (CCD) is an inherited disorder of intestinal electrolyte transport that results in a large wastage of electrolytes and water. The patient, who is now 24 years old, was diagnosed at the age of 16 months with CCD based on hypochloremic alkalosis, hyponatremia, and hypokalemia with increased plasma renin and aldosterone levels, and high fecal Cl(-). Serum Na(+) and plasma aldosterone levels were normalized by replacement therapy with NaCl [8 mmol/(kg day)] and KCl [3 mmol/(kg day)]. On follow-up, watery diarrhea persisted, and she was frequently noted to have hypokalemia despite normal serum Na(+) and Cl(-) and plasma aldosterone levels with only reduced dosages of KCl [1-1.5 mmol/(kg day)] substitution due to only sporadic ambulatory care and unsatisfactory compliance with medication, and a normal diet. However, she had acceptable growth, normal renal function, and had an uneventful pregnancy and delivery of a healthy child. In adolescence and adulthood, hypokalemia may be the main problem requiring treatment, and substitution therapy with adequate doses of KCl alone may be sufficient, although a combination of NaCl and KCl is generally recommended even after childhood.

Long-term clinical outcome in patients with congenital chloride diarrhea

OBJECTIVES

Congenital chloride diarrhea (CLD) is a rare, autosomal recessive disorder of intestinal Cl/HCO3 exchange caused by mutations in the SLC26A3 gene and characterized by persistent Cl rich diarrhea from birth. Treatment is symptomatic and replacement therapy with NaCl and KCl has been shown to be effective in children, but the long-term prognosis remains unclear. We studied the largest known cohort of patients to evaluate the long-term outcome of CLD and to search for extraintestinal manifestations.

METHODS

This is a cross-sectional clinical evaluation and retrospective analysis of medical history of 36 Finnish patients with CLD, born in the 1960s (n = 8), 1970s (n = 7) and 1980s (n = 21).

RESULTS

Early diagnosis and aggressive salt replacement therapy were associated with normal growth and development, in addition to significantly reduced mortality rates among the groups of patients born in the different decades, respectively (P = 0.001). No deaths due to CLD were observed after 1972. Enuresis, slight soiling and hospitalizations for gastroenteritis were common, especially in childhood, but 92% of the patients found their health excellent or good. Complications documented were end-stage renal disease (n = 1) and hyperuricemia (n = 4), novel findings possibly associated with CLD being male subfertility (n = 3), spermatoceles (n = 3), intestinal inflammation (n = 2), inguinal hernias (n = 4) and increased concentrations of sweat Cl in 12% of the patients.

CONCLUSIONS

When early diagnosed and adequately treated, the long-term prognosis of CLD is favorable. A putative role of a primary anion exchange defect of SLC26A3 in male subfertility and the decline of renal function due to chronic dehydration deserve further characterization.

Disruption of the SLC26A3-mediated anion transport is associated with male subfertility

Male subfertility in congenital chloride diarrhea (CLD) was possible after identification of expression of an epithelial Cl-/HCO3- exchanger SLC26A3 in the male reproductive tract and by the observation that adult men with CLD had very few children. A prospective clinical and laboratory study among eight adult Finnish men with CLD revealed constant oligoasthenoteratozoospermia but normal spermatogenesis, high chloride and low pH in seminal plasma, and three spermatoceles, suggesting that male subfertility is a clinical manifestation of CLD and could be caused by an analogous defect in the epithelial Cl-/HCO3- and water transport, as described for the CLD intestine.

Butyrate as an effective treatment of congenital chloride diarrhea

BACKGROUND & AIMS

Many therapeutic attempts have demonstrated to be ineffective in reducing the severity of congenital chloride diarrhea and its long-term complications. The short-chain fatty acid butyrate stimulates intestinal water and ion absorption through a variety of mechanisms, including the activation of a parallel Cl-/butyrate and Na+/H+ exchanger. In this case report, we report the therapeutic efficacy of butyrate on an 11-year-old patient affected by congenital chloride diarrhea.

METHODS

The efficacy of increasing doses of oral butyrate (from 50 to 100 mg/kg/day) was investigated through the daily evaluation of stool volume, bowel movements, fecal incontinence, serum, and stool electrolytes concentrations. The modifications in transepithelial intestinal ion transport elicited by butyrate were examined by rectal dialysis study.

RESULTS

A butyrate dose of 100 mg/kg/day induced a normalization of stool pattern and of serum and fecal electrolytes concentration. The rectal dialysis study demonstrated a proabsorptive effect induced by butyrate on Na+, Cl-, and K+ intestinal transport. Butyrate therapy was well tolerated during the entire 12-month observation period, and the stool pattern and fecal and serum ion concentrations remained stable within the normal ranges. No clinical adverse events or episodes of dehydration requiring hospital care were observed.

CONCLUSIONS

Butyrate could be effective in treating congenital chloride diarrhea. It is easily administered, useful in preventing severe dehydration episodes, and may be a promising therapeutic approach for a long-term treatment in this rare and severe condition.

The SLC26 gene family of multifunctional anion exchangers

The ten-member SLC26 gene family encodes anion exchangers capable of transporting a wide variety of monovalent and divalent anions. The physiological role(s) of individual paralogs is evidently due to variation in both anion specificity and expression pattern. Three members of the gene family are involved in genetic disease; SLC26A2 in chondrodysplasias, SLC26A3 in chloride-losing diarrhea, and SLC26A4 in Pendred syndrome and hereditary deafness (DFNB4). The analysis of Slc26a4-null mice has significantly enhanced the understanding of the roles of this gene in both health and disease. Targeted deletion of Slc26a5 has in turn revealed that this paralog is essential for electromotor activity of cochlear outer hair cells and thus for cochlear amplification. Anions transported by the SLC26 family, with variable specificity, include the chloride, sulfate, bicarbonate, formate, oxalate and hydroxyl ions. The functional versatility of SLC26A6 identifies it as the primary candidate for the apical Cl(-)-formate/oxalate and Cl(-)-base exchanger of brush border membranes in the renal proximal tubule, with a central role in the reabsorption of Na(+)-Cl(-) from the glomerular ultrafiltrate. At least three of the SLC26 exchangers mediate electrogenic Cl(-)-HCO(3)(-) and Cl(-)-OH(-) exchange; the stoichiometry of Cl(-)-HCO(3)(-) exchange appears to differ between SLC26 paralogs, such that SLC26A3 transports >/=2 Cl(-) ions per HCO(3)(-) ion, whereas SLC26A6 transports >/=2 HCO(3)(-) ions per Cl(-) ion. SLC26 Cl(-)-HCO(3)(-) and Cl(-)-OH(-) exchange is activated by the cystic fibrosis transmembrane regulator (CFTR), implicating defective regulation of these exchangers in the reduced HCO(3)(-) transport seen in cystic fibrosis and related disorders; CFTR-independent activation of these exchangers is thus an important and novel goal for the future therapy of cystic fibrosis.

Neonatal enteropathies: defining the causes of protracted diarrhea of infancy

The underlying causes of chronic diarrhea beginning early in life are increasingly well defined. Infectious and post-infectious enteropathies and food sensitive/allergic enteropathy account for the majority of cases. Recent attention has focused on characterizing defined entities, which cause protracted diarrhea in infants and young children. Disorders of intestinal ion transport usually present at birth following a pregnancy complicated by polyhydramnios. Intestinal mucosal biopsies show normal architect with intact villus-crypt axis. Neonatal enteropathies, by contrast, are characterized by blunting of the villi. These include microvillus inclusion disease, tufting enteropathy, autoimmune enteropathy and IPEX syndrome - and it is these conditions that are the subject of the current review.

Acute regulation of the SLC26A3 congenital chloride diarrhoea anion exchanger (DRA) expressed in Xenopus oocytes

Mutations in the human SLC26A3 gene, also known as down-regulated in adenoma (hDRA), cause autosomal recessive congenital chloride-losing diarrhoea (CLD). hDRA expressed in Xenopus oocytes mediated bidirectional Cl--Cl- and Cl--HCO3- exchange. In contrast, transport of oxalate was low, and transport of sulfate and of butyrate was undetectable. Two CLD missense disease mutants of hDRA were nonfunctional in oocytes. Truncation of up to 44 C-terminal amino acids from the putatively cytoplasmic C-terminal hydrophilic domain left transport function unimpaired, but deletion of the adjacent STAS (sulfate transporter anti-sigma factor antagonist) domain abolished function. hDRA-mediated Cl- transport was insensitive to changing extracellular pH, but was inhibited by intracellular acidification and activated by NH4+ at acidifying concentrations. These regulatory responses did not require the presence of either hDRA's N-terminal cytoplasmic tail or its 44 C-terminal amino acids, but they did require more proximate residues of the C-terminal cytoplasmic domain. Although only weakly sensitive to inhibition by stilbenes, hDRA was inhibited with two orders of magnitude greater potency by the anti-inflammatory drugs niflumate and tenidap. cAMP-insensitive Cl--HCO3- exchange mediated by hDRA gained modest cAMP sensitivity when co-expressed with cystic fibrosis transmembrane conductance regulator (CFTR). Despite the absence of hDRA transcripts in human cell lines derived from CFTR patients, DRA mRNA was present at wild-type levels in proximal colon and nearly so in the distal ileum of CFTR(-/-) mice. Thus, pharmacological modulation of DRA might be a useful adjunct treatment of cystic fibrosis.

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.

SLC26A3 mutations in congenital chloride diarrhea

Congenital chloride diarrhea (CLD) is an autosomal recessive disorder of intestinal electrolyte absorption. It is characterized by persistent secretory diarrhea resulting in polyhydramnios and prematurity prenatally, and dehydration, hypoelectrolytemia, hyperbilirubinemia, abdominal distention, and failure to thrive immediately after birth. CLD is caused by mutations in the solute carrier family 26, member 3 gene (SLC26A3, alias CLD or DRA), which encodes a Na+-independent Cl-/HCO3- (or OH-) exchanger. SLC26A3 is a member of the SLC26 sulfate permease/anion transporter family and it is expressed mainly in the apical brush border of intestinal epithelium. The only extraintestinal tissues showing SLC26A3 expression are eccrine sweat glands and seminal vesicles. A wide variety of different mutations in the SLC26A3 gene have been associated with CLD with no apparent evidence of phenotype-genotype correlation. The clinical course of CLD, however, is variable and may rather depend on environmental factors and compensatory mechanisms than mutations. In this report, we present a summary of all published and two novel SLC26A3 mutations and polymorphisms, and review them in the context of their functional consequences and clinical implications.

Identification of seven novel mutations including the first two genomic rearrangements in SLC26A3 mutated in congenital chloride diarrhea

Congenital chloride diarrhea (CLD) is an autosomal recessive disorder characterized by defective intestinal electrolyte absorption, resulting in voluminous osmotic diarrhea with high chloride content. A variety of mutations in the solute carrier family 26, member 3 gene (SLC26A3, previously known as CLD or DRA) are responsible for the disease. Since the identification of the SLC26A3 gene and the determination of its genomic structure, altogether three founder and 17 private mutations have been characterized within miscellaneous ethnic groups. We screened for mutations in seven unrelated families with CLD. The diagnoses were confirmed by fecal chloride measurements. The combined PCR-SSCP and sequencing analyses revealed altogether seven novel mutations including two missense mutations (S206P, D468V), two splicing defects (IVS12-1G>C, IVS13-2delA), one nonsense mutation (Q436X), one insertion/deletion mutation (2104-2105delGGins29-bp), and an intragenic deletion of SLC26A3 exons 7 and 8. Two previously identified mutations were also found. This is the first report of rearrangement mutations in SLC26A3. Molecular features predisposing SLC26A3 for the two rearrangements may include repetitive elements and palindromic-like sequences. The increasingly wide diversity of SLC26A3 mutations suggests that mutations in the SLC26A3 gene may not be rare events.