Clinical Description
Shwachman-Diamond syndrome (SDS) is characterized by exocrine pancreatic dysfunction with malabsorption, malnutrition, and growth failure; hematologic abnormalities with single- or multilineage cytopenias and susceptibility to myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML); and bone abnormalities. To date, more than 500 individuals have been identified with biallelic pathogenic variants in DNAJC21, EFL1, or SBDS or a heterozygous pathogenic variant in SRP54. The following description of the phenotypic features associated with this condition is based on these reports [Han et al 2023].
Table 2.
Shwachman-Diamond Syndrome: Frequency of Select Features
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Feature | % of Persons w/Feature |
---|
Exocrine pancreatic dysfunction | >90% |
Cytopenia(s) | >95% |
Myelodysplastic syndrome | 10% |
Skeletal manifestations | 60% |
Poor weight gain &/or growth delay | 80% |
Presentation. Neonates generally do not show manifestations of SDS; however, early presentations have included acute life-threatening infections, severe bone marrow failure, aplastic anemia [Kuijpers et al 2005], asphyxiating thoracic dystrophy caused by rib cage restriction, and severe spondylometaphyseal dysplasia [Nishimura et al 2007].
More commonly, SDS presents in infancy with poor weight gain and poor growth secondary to exocrine pancreatic dysfunction. However, the presentation of SDS varies greatly, with nearly half of individuals in the North American SDS Registry presenting without neutropenia or steatorrhea [Myers et al 2014].
Exocrine pancreatic dysfunction results from severe depletion of pancreatic acinar cells. The manifestations of pancreatic dysfunction are most evident in the first year of life, often in the first six months. Severity can vary widely from asymptomatic to severe dysfunction with significant malabsorption of nutrients, steatorrhea, poor weight gain, and growth delay. For unclear reasons, the clinical manifestations of pancreatic dysfunction resolve with age; up to 50% of individuals are able to discontinue pancreatic enzyme supplementation and have normal fat absorption by age four years, even when pancreatic enzyme secretion is less than normal [Mack et al 1996].
Pancreatic histopathology reveals few acinar cells and extensive fatty infiltration. Pancreatic imaging studies by ultrasound or CT examination may reveal small pancreas size for age. In individuals with SBDS-related SDS, MRI revealed fatty infiltration with retained ductal and islet components [Toiviainen-Salo et al 2008b].
Additional gastrointestinal manifestations. A general acinar defect has also been identified, with increased parotid acinar dysfunction in persons with SDS compared to controls [Stormon et al 2010]. Duodenal inflammation was identified on gastrointestinal mucosal biopsies in more than 50% of symptomatic individuals with SDS [Shah et al 2010], suggesting a possible enteropathic component to their disease. This enteropathy may contribute to vitamin deficiencies observed in some individuals with SDS despite nutritional supplementation and enzymatic replacement [Pichler et al 2015].
Hematologic abnormalities. Neutropenia and impaired neutrophil chemotaxis are likely the most critical contributors to recurrent infections seen in young children [Dror & Freedman 2002, Stepanovic et al 2004, Kuijpers et al 2005]. Despite impaired neutrophil chemotaxis, individuals with SDS maintain the ability to form empyema and abscess, in contrast to other disorders of neutrophil chemotaxis [Aggett et al 1979, Rothbaum et al 1982]. Acute and deep-tissue infections can be life-threatening, particularly in young children [Cipolli 2001, Grinspan & Pikora 2005]. Persistent or intermittent neutropenia is recognized first in almost all (88%-100%) affected children, often before the diagnosis of SDS is identified [Ginzberg et al 1999].
Although anemia and thrombocytopenia are also seen in the majority of individuals with SDS, these findings may be intermittent or clinically asymptomatic. Severe aplastic anemia with pancytopenia occurs in a subset of individuals. The French Severe Chronic Neutropenia Registry found that 41/102 (40%) individuals with SDS demonstrated significant hematologic manifestations, including those with intermittent severe cytopenias and 21 with persistent severe cytopenias (nine classified as malignant, nine as nonmalignant, and three progressing from nonmalignant to malignant) [Donadieu et al 2012].
The risk for MDS or progression to leukemia, typically AML, is significant in individuals with SDS; however, data remain limited, with specific reports varying by definition of MDS and cohort age. In one 25-year survey, seven of 21 individuals with SDS developed MDS; five of these seven developed AML [Smith et al 1996]. The Severe Congenital Neutropenia International Registry reported an overall incidence of 8.1% of MDS/AML in 37 individuals with SDS over a ten-year period, representing a 1% per year rate of progression to MDS or AML [Dale et al 2006, Rosenberg et al 2006]. A cumulative transformation rate of 18% was reported in 34 individuals with SDS by the Canadian Inherited Bone Marrow Failure Study [Hashmi et al 2011]. In 55 individuals with SDS in the French Severe Chronic Neutropenia Registry, rates of transformation to MDS/AML were 18.8% and 36.1% at 20 years and 30 years, respectively [Donadieu et al 2012].
Of note, the above findings contrast with other reports from the Israeli Inherited Bone Marrow Failure Registry (3 individuals) [Tamary et al 2010] and an NIH inherited bone marrow failure syndromes cohort (17 individuals) [Alter et al 2010] in which no one developed MDS/AML. Conclusions remain difficult given the small sample sizes; however, these differences may be attributable to cohort age [Myers et al 2013a].
The risk for malignant transformation involving dysplasia or AML is considered to be lifelong, with AML generally associated with poor outcome [Donadieu et al 2005].
Individuals with SDS may develop characteristic cytogenetic clonal changes such as deletion of 20q11 and isochromosome 7 in the absence of overt MDS or AML. It has been suggested that these changes may persist and fluctuate over time without high risk of progression to MDS/AML [Cunningham et al 2002, Crescenzi et al 2009, Maserati et al 2009, Khan et al 2021]. Novel cytogenetic abnormalities in the presence or absence of deletion of 20q11 and isochromosome 7 have been reported in a cohort of 91 Italian individuals with SDS, including unbalanced structural anomalies of chromosome 7, complex rearrangements of the deletion of 20q, and unbalanced translocation with partial trisomy 3q and partial monosomy 6q [Valli et al 2017].
Survival remains poor for individuals that develop MDS/AML [Myers et al 2020a]; some individuals are diagnosed with MDS/AML on their first bone marrow biopsy, highlighting the need for prompt and regular surveillance upon diagnosis.
Recent evidence has suggested acquired pathogenic variants in hematopoietic cells in individuals with SDS can either alleviate ribosomal defects or increase leukemogenic potential via disruption of cellular checkpoints; somatic biallelic loss-of-function TP53 pathogenic variants in individuals with SDS are associated with myeloid malignancies [Kennedy et al 2021, Reilly & Shimamura 2023].
To date, other reported malignancies in individuals with SDS have been rare, including isolated reports of bilateral breast cancer [Singh et al 2012], dermatofibrosarcoma [Sack et al 2011], pancreatic adenocarcinoma, central nervous system lymphoma [Sharma et al 2014], and ovaran and esophageal carcinoma [Bou Mitri et al 2021].
Growth. Children with SDS who are provided with adequate nutrition and pancreatic enzyme supplementation have normal growth velocity and appropriate weight for height; however, approximately 50% of all children with SDS are below the third percentile for height and weight [Durie & Rommens 2004]. SDS-specific growth charts have been developed and are helpful to track growth velocity in individuals with SDS [Pegoraro et al 2024]. Growth hormone can be used to treat growth hormone deficiency with resultant improvement in growth velocity and height [Bogusz-Wójcik et al 2021].
Characteristic skeletal changes appear to be present in all individuals with a molecularly confirmed diagnosis [Mäkitie et al 2004]; however, skeletal manifestations vary among individuals and over time. In some individuals the skeletal findings may be subclinical.
Cross-sectional and longitudinal data from Mäkitie et al [2004] revealed:
Delayed appearance of secondary ossification centers, causing bone age to appear to be delayed;
Variable widening and irregularity of the metaphyses in early childhood, followed by progressive thickening and irregularity of the growth plates;
Generalized osteopenia.
Of note, the epiphyseal maturation defects tended to normalize with age and the metaphyseal changes tended to progress (worsen) with age [Mäkitie et al 2004].
Further skeletal findings can include rib and joint abnormalities, the latter of which can result from asymmetric growth and can be sufficiently severe to warrant surgical intervention.
Additionally, low-turnover osteoporosis has been reported as a feature of SDS. Toiviainen-Salo et al [2007] reported bone abnormalities in 10/11 individuals with molecularly confirmed SDS, including reduced bone mineral density. Vertebral compression fractures were reported in three individuals, and vitamin D and K deficiencies, both detrimental to bone health, were each identified in six individuals. It is important to ensure accurate measurement of bone mineral density, as adults with SDS have short stature and may have an incorrectly reported low bone mineral density due to low height z score [Shankar et al 2017].
Liver manifestations. Hepatomegaly and liver dysfunction with elevated serum aminotransferase concentrations can be observed in young children but tend to resolve by age five years [Toiviainen-Salo et al 2007]. Elevated bile acids were reported in seven of 12 individuals in one Finnish study, three of whom had persistent or intermittent elevation over time, raising concern for ongoing cholestasis [Toiviainen-Salo et al 2009]. Mild histologic changes may also be evident in liver biopsies, and although they do not appear to be progressive, liver complications have occurred in older individuals following bone marrow transplantation [Ritchie et al 2002]. Mitochondrial abnormalities have been described, which may mimic histologic characteristics seen in inborn errors of metabolism [Kaufman et al 2024], and early-onset cirrhosis has also been reported [Reddy et al 2023].
Cognitive/psychological. Individuals with SDS have been reported to have cognitive and/or behavioral impairment as well as structural brain changes, including decreased brain volume and smaller posterior fossa [Kent et al 1990, Cipolli et al 1999, Ginzberg et al 1999, Toiviainen-Salo et al 2008a, Perobelli et al 2012, Booij et al 2013, Perobelli et al 2015]. Kerr et al [2010] compared the neuropsychological function of 32 children with SDS with age- and sex-matched children with cystic fibrosis and sib controls. On a number of measures, those with SDS displayed a far wider range of abilities than controls, from severely impaired to superior. Approximately 20% of children with SDS demonstrated intellectual disability in at least one area, with perceptual reasoning being most affected. They were also far more likely than the general population to have the diagnosis of pervasive developmental disorder (6% vs 0.6%). Attention deficits were also more common in children with SDS and in their unaffected sibs than in children with cystic fibrosis.
Other reported findings