Evidence of a Generalized Defect of Acinar Cell Function in Shwachman-Diamond Syndrome

Background: Because the acinar cells of the exocrine pancreas in patients with Shwachman-Diamond syndrome (SDS) are severely depleted, we hypothesized that a similar deficiency may be present in acinar cells of the parotid gland. Patients and Methods: We determined serum pancreatic isoamylase and parotid amylase activities in 16 patients with SDS, 13 healthy controls, and 13 disease controls (cystic fibrosis or fibrosing pancreatitis). Parotid amylase and electrolyte concentrations were measured in stimulated parotid gland secretions. Starch digestion was assessed by breath hydrogen testing in patients with SDS (with and without enzyme supplements) and healthy controls. Results: Serum pancreatic and parotid isoamylase values were lower in the patients with SDS than in the healthy controls (P<0.0001 and P=0.0002, respectively). Serum pancreatic isoamylase, but not parotid isoamylase, was significantly lower in the disease controls than in the healthy controls (P<0.0001 and P=0.17, respectively). Secreted parotid gland amylase concentration (units per milligram of protein) in patients with SDS was lower than that in the healthy controls (P=0.04), whereas the disease controls were comparable to the healthy subjects (P=0.09). Secreted parotid chloride concentration was inversely correlated with amylase concentration in the patients with SDS (P=0.01), but no correlation was seen in the healthy controls or disease controls. When patients with SDS ingested starch without enzyme supplementation, their breath hydrogen excretion was significantly higher than that in the healthy controls (P=0.009). Following starch ingestion with enzymes, breath hydrogen in the patients with SDS was lower (P<0.05) than with no enzyme treatment, and no different from controls (P=0.37). Conclusions: Mutations in the SBDS gene cause a generalized functional abnormality of exocrine acinar cells.