Spondyloenchondrodysplasia in five new patients: identification of three novel ACP5 variants with variable neurological presentations

Clinical, laboratory, and molecular characteristics of patients with spondyloenchondrodysplasia: a case series study

Spondyloenchondrodysplasia (SPENCD) is a rare genetic disorder characterized with skeletal dysplasia, immune dysregulation, and neurological impairment. Patients diagnosed with SPENCD at a single pediatric hematology center were included in the study. The patients' clinical characteristics, symptoms at presentation, imaging and laboratory results, and genetic analysis results were collected retrospectively from their files. This study evaluated nine patients diagnosed with SPENCD, eight of whom had autoimmune manifestations at presentation. Common findings included autoimmune hemolytic anemia, hypothyroidism, and elevated transaminase levels. All patients exhibited short stature and skeletal abnormalities. Neurological symptoms were present in six patients, with intracranial calcifications detected in five. Recurrent bacterial and viral infections, including respiratory tract infections, were prevalent. The NM_001611.5 (ACP5): c.772_790del p.(Ser258TrpfsTer39) frameshift variant was identified in all patients. Two patients died during follow-up.

CONCLUSION

The study highlights the clinical characteristics and challenges associated with SPENCD. The findings underscore the need for comprehensive management strategies to address the multifaceted complications associated with SPENCD.

WHAT IS KNOWN

• Spondyloenchondrodysplasia (SPENCD) is classified as a type-1 interferonopathy resulting from homozygous mutations in the ACP5 gene, which leads to a deficiency in tartrate-resistant acid phosphatase. • The clinical features associated with this condition encompass skeletal dysplasia, spastic paraparesis, short stature, thrombocytopenia, hemolytic anemia, and systemic lupus erythematosus like autoimmune manifestations. Additionally, patients may experience intracranial calcifications and recurrent infections.

WHAT IS NEW

• SPENCD exhibits similarities with other type I interferonopathies, including increased levels of type I interferon and specific neurological symptoms; however, it also displays distinct characteristics such as intellectual disability and behaviors associated with autism spectrum disorder. • Despite the rare occurence of the condition and the small number of patients reported here the findings underscore the complexity of managing this condition, particularly in the context of consanguinity and the associated risks of severe complications and mortality.

Nucleotide metabolism, leukodystrophies, and CNS pathology

The balance between a protective and a destructive immune response can be precarious, as exemplified by inborn errors in nucleotide metabolism. This class of inherited disorders, which mimics infection, can result in systemic injury and severe neurologic outcomes. The most common of these disorders is Aicardi Goutières syndrome (AGS). AGS results in a phenotype similar to "TORCH" infections (Toxoplasma gondii, Other [Zika virus (ZIKV), human immunodeficiency virus (HIV)], Rubella virus, human Cytomegalovirus [HCMV], and Herpesviruses), but with sustained inflammation and ongoing potential for complications. AGS was first described in the early 1980s as familial clusters of "TORCH" infections, with severe neurology impairment, microcephaly, and basal ganglia calcifications (Aicardi & Goutières, Ann Neurol, 1984;15:49-54) and was associated with chronic cerebrospinal fluid (CSF) lymphocytosis and elevated type I interferon levels (Goutières et al., Ann Neurol, 1998;44:900-907). Since its first description, the clinical spectrum of AGS has dramatically expanded from the initial cohorts of children with severe impairment to including individuals with average intelligence and mild spastic paraparesis. This broad spectrum of potential clinical manifestations can result in a delayed diagnosis, which families cite as a major stressor. Additionally, a timely diagnosis is increasingly critical with emerging therapies targeting the interferon signaling pathway. Despite the many gains in understanding about AGS, there are still many gaps in our understanding of the cell-type drivers of pathology and characterization of modifying variables that influence clinical outcomes and achievement of timely diagnosis.

Case report: Refractory Evans syndrome in two patients with spondyloenchondrodysplasia with immune dysregulation treated successfully with JAK1/JAK2 inhibition

Biallelic mutations in the ACP5 gene cause spondyloenchondrodysplasia with immune dysregulation (SPENCDI). SPENCDI is characterized by the phenotypic triad of skeletal dysplasia, innate and adaptive immune dysfunction, and variable neurologic findings ranging from asymptomatic brain calcifications to severe developmental delay with spasticity. Immune dysregulation in SPENCDI is often refractory to standard immunosuppressive treatments. Here, we present the cases of two patients with SPENCDI and recalcitrant autoimmune cytopenias who demonstrated a favorable clinical response to targeted JAK inhibition over a period of more than 3 years. One of the patients exhibited steadily rising IgG levels and a bone marrow biopsy revealed smoldering multiple myeloma. A review of the literature uncovered that approximately half of the SPENCDI patients reported to date exhibited increased IgG levels. Screening for multiple myeloma in SPENCDI patients with rising IgG levels should therefore be considered.