Variable Clinical Phenotype and Course In Greek Patients with Shwachman-Diamond Syndrome Carrying Identical SBDS Mutations

Shwachman-Diamond syndrome (SDS) is a rare multi-system genetic disorder mainly characterized by exocrine pancreatic insufficiency, bone marrow failure and skeletal abnormalities. Approximately 90% of patients meeting the clinical diagnostic criteria for SDS have mutations in the SBDS gene, located in chromosome 7q11. No genotype-phenotype correlations have been observed in patients with SDS.

Greek patients with similar SBDS mutations are included in this report. They were selected from the series of patients referred to our unit for SBDS gene molecular analysis due to pancreatic insufficiency and impaired hematopoiesis.

Patient 1 presented at birth with respiratory difficulties, hypotonia, anemia, neutropenia and thrombocytopenia. She has congenital anomalies including thoracic dystrophy, digit abnormalities, open foramen ovale and hypertelorism. She was found to have myelodysplasia with a bone marrow clone carrying i(7q) chromosomal abnormality in around 32% of the bone marrow cells. Pancreatic insufficiency was clinically evident even at the age of 5 months.

Patient 2 has chronic thrombocytopenia ranging between 40.000/μ L to 147.000/μ L, first presenting at the age of 7 years old. She has metaphyseal dysostosis, flared anterior end of ribs, open foramen ovale and growth hormone deficiency. Her pancreatic insufficiency is present from the age of 16 months.

Patient 3 (sister of patient 2) has borderline neutropenia, short stature, metaphyseal dysostosis, open foramen ovale and mild pancreatic insufficiency.

Patient 4 has thrombocytopenia since the age of 19 years old. She has stable clonal erythropoesis with a clone carrying the 46,X,del(X)(q24→qter) in 45% of the bone marrow cells. She presents recurrent bacterial infections, particularly bartholinitis. She has mild pancreatic insufficiency.

Patient 5 presented with chronic neutropenia and decreaced IgA since the age of 2 months. At the age of 12 months she presented hepatomegaly and elevated liver enzymes. Pancreatic insufficiency initially presented in infancy but improved gradually.

Genomic DNA was extracted from peripheral blood lymphocytes and molecular analysis with ECMA (Enzymatic Cleavage Mismatch Analysis), RFLPS and direct sequencing was performed allowing detection and characterization of disease causing mutations. PCR primers were specifically designed to amplify the whole coding region (five exons) and the flanking intron/exon junctions of SBDS gene but not the SBDSP pseudogene. RFLPs used the Bsu36I and AciI enzymes for the detection of the two most common c.183-184 TA>CT and 258+2 T>C mutations respectively.

All five patients were compound heterozygotes for 183–184 TA>CT and 258+2 T>C, which are the two most common mutations of SDS. One of those (patient 3) was found to be a mosaic which seems to explain the very mild phenotype, and another (patient 5) presented homozygosity for the 258+2 T>C while carrying the 183–184 TA>CT mutation as well.

Patient 1 was successfully transplanted by her HLA-identical sister at the age of 12 months. Her pancreatic insufficiency has not improved and she is still on pancreatic enzyme supplementation. Patient 2 is receiving pancreatic enzyme supplementation and also is currently on growth hormone supplementation. Patients 3 and 4 are not receiving pancreatic enzyme supplementation or granulocyte colony-stimulating factor. Patient 5 is currently receiving only granulocyte colony-stimulating factor.

Extreme variability ranging from severe clinical phenotype apparent at birth to close-to- normal phenotype in early adulthood was noted in this small series of Greek patients, carrying similar SBDS mutations. Moreover, gene conversion seems to be a frequent event in the SBDS gene. Further studies to evaluate the heterogeneity and the factors affecting the phenotype/genotype relationship in SDS are warranted.

No relevant conflicts of interest to declare.