Congenital and Putatively Acquired Forms of Sucrase-isomaltase Deficiency in Infancy: Effects of Sacrosidase Therapy

Sucrase-isomaltase (SI) is localised at the brush-border membrane of the small intestine and is responsible for the hydrolysis of sucrose and other carbohydrates such as palatinose ^(1,2). Deficiency of this enzyme leads to sucrose and glucan malabsorption resulting in osmotic diarrhoea. Onset of clinical symptoms is usually after the first year of life when sucrose consumption increases. This often results in failure to thrive ^(3,4). Clinical reports on patients with SI deficiency (SID) are rare. Only limited information about therapeutic success is available in the literature ^(5–7). We present 4 patients, 3 with congenital and 1 with a putatively acquired SID, who clinically improved after therapy with sacrosidase was initiated.

MATERIALS AND METHODS

We describe 3 patients who were admitted to hospital because of chronic diarrhoea and dystrophy, and 1 infant who was diagnosed on the basis of 2 index cases in the family before symptoms set in. All of the patients were of German origin. Family histories were unremarkable. Patients 1, 2, and 3 were siblings. The activities of the disaccharidases lactase, sucrase, isomaltase, and maltase in duodenal biopsy specimens were measured according to Asp et al ⁽⁸⁾. The results are depicted in Table 1.

TABLE 1: Activities of disaccharidases in units per gram protein measured in small intestine biopsies

DNA Amplification and DNA Sequencing

All 48 exons of the human SI gene (for reference sequence, see GeneBank accession number NC_000003, region 166179380–166278976) were amplified by polymerase chain reaction (PCR) for mutation analysis. Primers were used as described previously ⁽⁹⁾. Genomic DNA was isolated from patient's blood, using a NucleoSpin Blood kit (Macherey Nagel, Düren, Germany). The PCR reaction was carried out in a 50-μL reaction volume containing 20 ng DNA, (1.25 U GoTaq Polymerase), 1.5 mmol/L MgCl₂ (Promega, Mannheim, Germany), and 5 mmol/L deoxyribonucleotide triphosphates (Fermentas, St Leon Rot, Germany). The amplification protocol was a standard 3-step PCR reaction according to the manufacturer's instructions. All of the PCR products were cleaned up with a NucloFast 96 PCR cleanup kit (Macherey Nagel, Düren, Germany). The sequencing reactions were carried out on a MegaBACE 1000 capillary sequencer by the Institute of Animal Breeding and Genetics, University of Veterinary Medicine Hannover (Hannover, Germany). The findings of the molecular genetic analyses are summarized in Table 2.

TABLE 2: Findings of the molecular genetic analysis in 4 patients with SID

Patient 1

The boy was born at 32 weeks of gestation. Birth weight was on the 75th percentile; there were no postpartum complications. At the age of 9 months, after initial breast-feeding and subsequent start with sucrose-containing food, he developed chronic diarrhoea with up to 12 watery stools per day. At the age of 15.5 months his body length was 70 cm (<3rd percentile) and body weight was 7710 g (<3rd percentile). Except for a protruding abdomen the internal status was normal. The gastroenterologic workup could exclude common causes of chronic diarrhoea (coeliac disease: histology, antibodies; cystic fibrosis: sweat test; infection: stool culture; allergy against cow's milk: immunoglobulins, antibodies; intestinal malformation: ultrasound). A duodenal biopsy was performed and SID was diagnosed. Sequencing of the coding exons of the SI gene revealed several point mutations that could be responsible for the deficiency (Table 2). Histology of the biopsy sample was normal.

Sucraid (sacrosidase) therapy (2 mL per meal) was started at the age of 4 years and the gastrointestinal symptoms stopped immediately. At the age of 6 years 3 months psychomotor development and internal status were normal. Body weight was 16.2 kg (3rd percentile); however, body length was 105 cm (5 cm below 3rd percentile). There was no evidence for growth hormone deficiency or thyroid dysfunction.

Patient 2

The girl is the second child of the family and the sister of patient 1. She was born at 40 weeks of gestation (birth weight 3120 g, birth length 48 cm). At the age of 6 months she developed diarrhoea, a protruding abdomen, and showed a decline of body weight after breast-feeding was stopped and sucrose-containing food was introduced. At the age of 13 months her body weight (7280 g) and body length (70 cm) were both below the 3rd percentile. Psychomotor development was normal. A duodenal biopsy was performed and SID diagnosed. As in the previous case, genetic analysis revealed mutations in the coding region of SI (Table 2). Again histology of the biopsy material was unrevealing.

The intake of Sucraid (2 mL per meal) resulted in relief of symptoms. At the age of 5 years psychomotor development was normal; her body weight was 15.2 kg (10th percentile) and body length was 100 cm (3rd percentile).

Patient 3

This patient was born at term and is the younger sister of patients 1 and 2. Genetic analysis revealed the same mutations as in her brother and sister (Table 2).

Initially she was breast-fed. Therapy with Sucraid (2 mL per meal) was started as soon as sucrose-containing food was introduced. Using this regimen, clinical symptoms could be completely prevented.

Patient 4

The girl was born at term after an uneventful pregnancy (birth weight 3690 g, birth length 53 cm). The postnatal period was unremarkable. She was breast-fed until the age of 5 months; thereafter, she was switched to cow's milk formula. At the age of 6 months she was treated with penicillin because of bronchitis. At the fourth day she developed watery diarrhoea up to 20 times per day, flatulence, and abdominal pain. Body weight decreased from the 90th to the 25th percentile in the next few months. Different dietary regimens were tested but did not lead to relief of symptoms. The gastrointestinal workup did not identify an underlying defect (cf, patient 1). At the age of 12 months a duodenal biopsy was performed and sucrase deficiency could be diagnosed. The activities of the disaccharidases are shown in Table 1. Histology of the duodenal biopsy was unrevealing.

The application of 2 mL Sucraid per meal resulted in relief of gastrointestinal symptoms and the patient gained weight again. At the age of 4 years 10 months her body weight was 20 kg (75th–90th percentile) and body length was 110.7 cm (50th–75th percentile). Her psychomotor development is normal. Molecular genetics did not reveal a common mutation for congenital SID (CSID) (Table 2).

Eighteen months after the introduction of Sucraid medication was reduced and finally stopped completely without clinical relapse. There were no dietary restrictions.

DISCUSSION

Differential diagnosis of chronic diarrhoea in infancy includes congenital intestinal malformations, infectious and postinfectious diseases, endocrine disorders, pseudomembranous colitis, coeliac disease, cystic fibrosis, toddler's diarrhoea/irritable bowel syndrome, and allergic gastroenteropathy. These diagnoses were excluded in our patients.

CSID is a rare autosomal recessive cause of sucrose malabsorption and should be included as a second-tier test for chronic diarrhoea. The introduction of a sucrose-containing diet in breast-fed or bottle-fed infants (receiving sucrose-free formula) suffering from this disease leads to intermittent watery diarrhoea, dystrophy, flatulence, and abdominal pain ^(3–5). Diagnosis is based on reduced activities of sucrase, isomaltase, and maltase in duodenal biopsy specimens from these children, whereas the activity of lactase as a reference enzyme is in the normal range. Prevalence of CSID seems to be higher than expected. In a white population Welsh et al ⁽¹⁰⁾ found a 2% incidence of heterozygotes, whereas Peterson and Herber ⁽¹¹⁾ found a frequency of 8.9% of heterozygous individuals in a US population. Clinical heterogeneity is due to diverse pathomechanisms that result from different molecular defects in CSID and influence the intracellular processing, intracellular transport, sorting, and insertion of the enzyme into the brush-border membrane ^(1,12,13).

In patients 1, 2, and 4 the typical clinical features of acquired or CSID (watery diarrhoea, abdominal symptoms, and failure to thrive) could be found. All of them showed a significant reduction of sucrase, maltase, and isomaltase activity in duodenal biopsy specimens, whereas the activity of lactase as a reference enzyme was normal. However, only in 3 of these patients could typical mutations for CSID be detected. The coding region of the SI gene of patient 4, however, contained 2 polymorphic alterations, which may in combination be responsible for the onset of the disease. However, Sucraid supplementation could gradually be reduced without clinical relapse. Therefore, this particular case represents an acquired form of SID.

Patient 3 was diagnosed by mutation analysis on the basis of 2 index cases in the same family. Symptoms in this patient could be prevented by giving her Sucraid as soon as sucrose-containing food was introduced.

Interestingly, 1 of the mutations identified in this communication, F1745C, has been also characterised as a heterozygous mutation in a screen of a cohort of patients in Hungary with typical symptoms of disaccharide malabsorption ⁽⁹⁾. The study has surprisingly suggested compound heterozygosity as a novel pathomechanism in CSID. The G563V has not been reported before in association with CSID and it is likely that this mutation affects the trafficking of SI because it is located in the vicinity of the stalk region of SI that is associated with its polarised sorting ⁽¹⁴⁾.

Strict adherence to sucrose-reduced diets is often difficult and does not result in complete relief of symptoms ⁽¹⁵⁾. A reduction in hydrogen excretion and a significant reduction in clinical symptoms could be shown in an enzyme-substitution trial (yeast Saccharomyces cerevisiae) with 8 patients suffering from CSID ⁽¹⁶⁾. The positive effect of liquid yeast–derived sucrase enzyme replacement could also be shown in a controlled double-blind trial with 14 patients and 28 patients with CSID, respectively ^(6,7).

All of the patients presented here improved under Sucraid therapy, and no adverse effects were observed. Thus, we could show that enzyme replacement with Sucraid is an effective and safe treatment for SID.

Conclusions

Because of phenotypic variations due to different disease-causing mutations in CSID, the disorder may remain undiagnosed in many cases. Because presumably acquired forms of SID may exist, we recommend the determination of disaccharidase activities by duodenal biopsy in any child with unclear chronic diarrhoea. Sucraid enzyme replacement is safe and effective in children with congenital and putatively acquired forms of SID.

Acknowledgments

We thank Orphan-Europe (Dietzenbach, Germany) for financial support towards mutation analysis.