Inborn errors of immunity and metabolic disorders: current understanding, diagnosis, and treatment approaches

The Etiologic Landscape of Lymphoproliferation in Childhood: Proposal for a Diagnostic Approach Exploring from Infections to Inborn Errors of Immunity and Metabolic Diseases

Lymphoproliferation is defined by lymphadenopathy, splenomegaly, hepatomegaly, or lymphocytic organ and tissue infiltration. The most common etiologies of lymphoproliferation are represented by infectious diseases and lymphoid malignancies. However, it is increasingly recognized that lymphoproliferative features can be the presenting sign of rare conditions, including inborn errors of immunity (IEI) and inborn errors of metabolism (IEM). Among IEI, lymphoproliferation is frequently observed in autoimmune lymphoproliferative syndrome (ALPS) and related disorders, common variable immunodeficiency (CVID), activated phosphoinositide 3-kinase δ syndrome, and Epstein-Barr virus (EBV)-related disorders. Gaucher disease and Niemann-Pick disease are the most common IEMs that can present with isolated lymphoproliferative features. Notably, other rare conditions, such as sarcoidosis, Castleman disease, systemic autoimmune diseases, and autoinflammatory disorders, should be considered in the differential diagnosis of patients with persistent lymphoproliferation when infectious and malignant diseases have been reasonably ruled out. The clinical features of lymphoproliferative diseases, as well as the associated clinical findings and data deriving from imaging and first-level laboratory investigations, could significantly help in providing the correct diagnostic suspicion for the underlying etiology. This paper reviews the most relevant diseases associated with lymphoproliferation, including infectious diseases, hematological malignancies, IEI, and IEM. Moreover, some practical indications to orient the initial diagnostic process are provided, and two diagnostic algorithms are proposed for the first-level assessment and the approach to persistent lymphoproliferation, respectively.

BNT162b2 COVID-19 vaccination elicited protective robust immune responses in pediatric patients with inborn errors of metabolism

Introduction

SARS-CoV-2 infection can lead to a life-threatening acute metabolic decompensation in children with inborn errors of metabolism (IEM), so vaccination is mandatory. However, IEMs can also impair innate or adaptive immunity, and the impact of these immune system alterations on immunogenicity and vaccine efficacy is still unknown. Here, we investigated humoral immune responses to the BNT162b2 mRNA COVID-19 vaccine and clinical outcomes in pediatric IEM patients.

Methods

Fifteen patients between 12-18 years of age with a confirmed diagnosis of IEM, and received BNT162b2 were enrolled to the study. Patients with an anti-SARS-CoV-2 IgG concentration >50 AU/mL before vaccination were defined as "COVID-19 recovered" whereas patients with undetectable anti-SARS-CoV-2 IgG concentration were defined as "COVID-19 naïve". Anti-SARS-CoV-2 Immunoglobulin G (IgG) and SARS-CoV-2 neutralizing antibody (nAb) titers were measured to assess humoral immune response.

Results

Anti-SARS-CoV-2 IgG titers and nAb IH% increased significantly after the first dose. The increase in antibody titers after first and second vaccination remained significant in COVID-19 naïve patients. Complete anti-SARS-CoV-2 IgG seropositivity and nAb IH% positivity was observed in all patients after the second dose. Vaccination appears to be clinically effective in IEM patients, as none of the patients had COVID-19 infection within six months of the last vaccination.

Discussion

Humoral immune response after two doses of BNT162b2 in pediatric IEM patients was adequate and the immune response was not different from that of healthy individuals.

100 years of inherited metabolic disorders in Austria-A national registry of minimal birth prevalence, diagnosis, and clinical outcome of inborn errors of metabolism in Austria between 1921 and 2021

Inherited metabolic disorders (IMDs) are a heterogeneous group of rare disorders characterized by disruption of metabolic pathways. To date, data on incidence and prevalence of IMDs are limited. Taking advantage of a functioning network within the Austrian metabolic group, our registry research aimed to update the data of the "Registry for Inherited Metabolic Disorders" started between 1985 and 1995 with retrospectively retrieved data on patients with IMDs according to the Society for the Study of Inborn Errors of Metabolism International Classification of Diseases 11 (SSIEM ICD11) catalogue. Included in this retrospective register were 2631 patients with an IMD according to the SSIEM ICD11 Classification, who were treated in Austria. Thus, a prevalence of 1.8/10 000 for 2020 and a median minimal birth prevalence of 16.9/100 000 (range 0.7/100 000-113/100 000) were calculated for the period 1921 to February 2021. We detected a male predominance (m:f = 1.2:1) and a mean age of currently alive patients of 17.6 years (range 5.16 months-100 years). Most common diagnoses were phenylketonuria (17.7%), classical galactosaemia (6.6%), and biotinidase deficiency (4.2%). The most common diagnosis categories were disorders of amino acid and peptide metabolism (819/2631; 31.1%), disorders of energy metabolism (396/2631; 15.1%), and lysosomal disorders (395/2631; 15.0%). In addition to its epidemiological relevance, the "Registry for Inherited Metabolic Disorders" is an important tool for enhancing an exchange between care providers. Moreover, by pooling expertise it prospectively improves patient treatment, similar to pediatric oncology protocols. A substantial requirement for ful filling this goal is to regularly update the registry and provide nationwide coverage with inclusion of all medical specialties.

Safety and recommendations for vaccinations of children with inborn errors of metabolism

Inborn errors of metabolism (IEM) are genetic disorders due to a defective metabolic pathway. The incidence of each disorder is variable and depends on the respective population. Some disorders such as urea cycle disorders (UCD) and organic acidurias, pose a high risk for a metabolic crisis culminating in a life-threatening event, especially during infections; thus, vaccines may play a crucial role in prevention. However, there are different triggers for decompensations including the notion that vaccines themselves can activate fever and malaise. Additionally, many of the IEM include immunodeficiency, placing the patients at an increased risk for infectious diseases and possibly a weaker response to immunizations. Since metabolic crises and vaccine regimens intersect in the first years of life, the question whether to vaccinate the child occupies parents and medical staff. Many metabolic experts hesitate to vaccinate IEM patients, disregarding the higher risk from the direct infections. In this paper we summarize the published data regarding the safety and recommendations for vaccinations in IEM patients, with reference to the risk for decompensations and to the immunogenic component.