Deficiency of secretory IgA (polymers of 2-4 IgA monomers are linked by two additional chains) and is the primary antibody response at the mucosal level, where it forms immune complexes with pathogens and allergens.

Glycogen storage disease type I (GSDI) is characterized by accumulation of glycogen and fat in the liver and kidneys resulting in hepatomegaly and nephromegaly. Severely affected infants present in the neonatal period with severe hypoglycemia due to fasting intolerance. More commonly, untreated infants present at age three to four months with hepatomegaly, severe hypoglycemia with or without seizures, lactic acidosis, hyperuricemia, and hypertriglyceridemia. Affected children typically have doll-like faces with full cheeks, relatively thin extremities, short stature, and a protuberant abdomen. Xanthoma and diarrhea may be present. Impaired platelet function and development of reduced or dysfunctional von Willebrand factor can lead to a bleeding tendency with frequent epistaxis and menorrhagia in females. Individuals with untreated GSDIb are more likely to develop impaired neutrophil and monocyte function as well as chronic neutropenia resulting in recurrent bacterial infections, gingivitis, periodontitis, and genital and intestinal ulcers. Long-term complications of untreated GSDI include short stature, osteoporosis, delayed puberty, renal disease (including proximal and distal renal tubular acidosis, renal stones, and renal failure), gout, systemic hypertension, pulmonary hypertension, hepatic adenomas with potential for malignancy, pancreatitis, and polycystic ovaries. Seizures and cognitive impairment may occur in individuals with prolonged periods of hypoglycemia. Normal growth and puberty are expected in treated children. Most affected individuals live into adulthood.

Immunodeficiency-40 is an autosomal recessive primary form of combined immunodeficiency mainly affecting T-cell number and function, with other more variable defects in B-cell and NK-cell function. Patients have onset of severe invasive bacterial and viral infections in early childhood and may die without bone marrow transplantation (summary by Dobbs et al., 2015).

Mitochondrial neurogastrointestinal encephalopathy (MNGIE) disease is characterized by progressive gastrointestinal dysmotility (manifesting as early satiety, nausea, dysphagia, gastroesophageal reflux, postprandial emesis, episodic abdominal pain and/or distention, and diarrhea); cachexia; ptosis/ophthalmoplegia or ophthalmoparesis; leukoencephalopathy; and demyelinating peripheral neuropathy (manifesting as paresthesias (tingling, numbness, and pain) and symmetric and distal weakness more prominently affecting the lower extremities). The order in which manifestations appear is unpredictable. Onset is usually between the first and fifth decades; in about 60% of individuals, symptoms begin before age 20 years.

MRD57 is an autosomal dominant neurodevelopmental disorder with a highly variable phenotype. Most affected individuals have delayed psychomotor development apparent in infancy or early childhood, language delay, and behavioral abnormalities. Additional features may include hypotonia, feeding problems, gastrointestinal issues, and dysmorphic facial features (summary by Reijnders et al., 2018).

Immunodeficiency-91 and hyperinflammation (IMD91) is an autosomal recessive complex immunologic disorder characterized by both immunodeficiency and recurrent infections, often to viruses or mycobacteria, as well as by hyperinflammation with systemic involvement. Affected individuals present in infancy with variable features, including fever, infection, thrombocytopenia, renal or hepatic dysfunction, recurrent infections, or seizures. Most patients eventually develop hepatic or renal failure, compromised neurologic function, lymphadenopathy or hepatosplenomegaly, and multiorgan failure resulting in death. More variable features may include intermittent monocytosis, features of hemophagocytic lymphohistiocytosis (HLH), and serologic evidence of hyperinflammation. The disorder is thought to result from dysregulation of the interferon response to viral stimulation in the innate immune system (summary by Le Voyer et al., 2021; Vavassori et al., 2021).

Neurodevelopmental disorder with epilepsy and brain atrophy (NEDEBA) is an autosomal recessive disorder characterized by early-onset progressive myoclonus epilepsy with ataxia (summary by Bott et al., 2021).

Neurodevelopmental disorder with absent speech and movement and behavioral abnormalities (NEDSMB) is an autosomal recessive disorder characterized by global developmental delay and severely impaired intellectual development with aggressive behavior. Mild dysmorphic features and hypodontia are also present (Faqeih et al., 2023).