Understanding DNAJC21-Related Shwachman-Diamond Syndrome

Receiving a diagnosis for an ultra-rare disease like DNAJC21-related Shwachman-Diamond Syndrome (SDS) can feel overwhelming. You may find that many doctors you encounter have never seen a case before, which can lead to a sense of isolation ^[1]. Please know that while the name is long and the condition is rare, there is a dedicated community of researchers and families working to understand and manage this disease [NCT06999954].

DNAJC21-related SDS is a genetic condition that belongs to a group of disorders called ribosomopathies—diseases caused by problems with how cells build ribosomes, the “factories” that make proteins ^[2]. Because proteins are essential for almost every function in the body, these defects can lead to a wide range of symptoms affecting the blood, growth, and various organs ^[3].

How Rare is This Condition?

DNAJC21-related SDS is significantly rarer than the more common version of the syndrome (caused by the SBDS gene). As of late 2023, fewer than 20 cases had been documented in the global medical literature, though true prevalence is unknown ^[1][3].

Because so few cases exist, doctors are still learning about the full spectrum of the disease. While early reports focused on severe childhood cases, more recent research has identified adults with milder symptoms, such as low platelet counts, suggesting the condition may be more variable than originally thought ^[1][4]. Keep in mind that clinical features and prognosis described below are drawn from small case series rather than large, reliable population categories.

The Biological “Glitch”: DNAJC21 vs. SBDS

To understand why this condition happens, it helps to look at how cells build their protein factories. Ribosomes are made of two main parts: the small subunit (40S) and the large subunit (60S). Both forms of SDS involve problems making the 60S subunit, but they happen at different times:

• Standard SDS (SBDS gene): Think of this as a problem late in the assembly line. A factor called eIF6 must be removed before the factory can start working. The SBDS protein works with EFL1 to promote this release ^[5].
• DNAJC21-related SDS: This involves a problem in early 60S ribosomal maturation. The DNAJC21 protein is needed for pre-rRNA processing and gathering the early components for the 60S subunit ^[2].

When DNAJC21 is missing or not working correctly, the cell cannot mature enough 60S subunits. This leads to aberrant ribosome profiles (malformed factories) and increased cell death, particularly in the bone marrow ^[2].

What to Expect: Clinical Features

DNAJC21-related SDS is a “multisystem” disorder, meaning it can affect many parts of the body. Because it is so rare, not everyone will have every symptom. Features reported in the literature include:

• Bone Marrow Failure: This is a prominent feature. The bone marrow may not produce enough white blood cells (neutropenia), red blood cells (anemia), or platelets (thrombocytopenia) ^[3][6].
• Pancreatic Issues: Some individuals have exocrine pancreatic insufficiency (EPI), where the pancreas doesn’t produce enough enzymes to digest food properly ^[3][6].
• Growth and Development: Many individuals experience growth retardation, difficulty gaining weight, or developmental delays ^[3][4].
• Physical Findings: Some individuals have unique physical features involving the skin, teeth, or hair. Abnormalities in the retina (back of the eye) or skeletal system, such as hip dysplasia, have also been reported in small case studies ^[3][4].

Prognosis and Long-Term Outlook

Because the number of known cases is so small, there is no “standard” life expectancy or fixed prognosis for DNAJC21-related SDS ^[7]. Some have severe bone marrow failure early in life, while others may have a more stable course into adulthood ^[1].

A primary concern is the risk of MDS (myelodysplastic syndrome) or AML (acute myeloid leukemia), which are blood cancers that can develop from marrow stress ^[2][3]. While the exact frequency of MDS/AML in DNAJC21 is not fully known, regular monitoring of blood counts and bone marrow—extrapolated from classic SDS guidance—is the standard way to manage this risk ^[3].

Research and Registries

Since this is an ultra-rare condition, participation in research registries is incredibly valuable, though optional.

• SDS Registry and Study: Based at Boston Children’s Hospital, this registry explicitly accepts patients with DNAJC21 mutations to study the natural history of the disease [NCT06056908].
• SDS Global Patient Survey: An online platform that allows families to share their experiences [NCT06999954].
• NCI Natural History Study: The National Cancer Institute (NCI) conducts a long-term study on inherited bone marrow failure syndromes [NCT00027274].