There are an increasing number of conditions in which a primary immunodeficiency (PID) has been described as one facet of a more complex disease setting. It is essential to consider associated diseases when a PID is identified as the primary manifestation and, conversely, not neglect the potentially harmful consequences of a PID that could be masked by other manifestations of a particular syndrome.
Below is a short description of these syndromes in which the PID is classified according to the arm of the immune system that is affected.
1. Primary Immunodeficiencies of the Innate Immune System
a) Several severe congenital neutropenia (SCN) syndromes can be associated with malformations. The recently described SCN disease caused by glucose-6-phosphatase deficiency (G6PC3) can be associated with heart and urogenital malformations. The related glycogenesis Ib disease combines SCN with hypoglycemia and hepatosplenomegaly. Some HAX-1 gene mutations lead to neurocognitive impairments as well as SCN. Barth syndrome combines SCN with cardiomyopathy. Lastly, Shwachman syndrome is a known autosomal recessive entity (caused by mutation of the SBDS gene) in which the defect in granulopoiesis can extend to the other hematopoietic lineages; short stature, bone metaphyseal dysplasia, and exocrine pancreatic insufficiency are known hallmarks of this condition.
d) A few patients with X-linked chronic granulomatous disease present with a contiguous gene deletion syndrome that can include the McLeod phenotype, which is characterized by anemia, acanthocytosis, and a severe risk of immune reaction against donor red cells because the patient's red cells do not express the Kell antigen. The McLeod phenotype also can result in a neurologic disease.
e) X-linked NF-kappa-B essential modulator (NEMO) deficiency provokes not only a variable set of deficiencies of both innate and adaptive immunity but also mild osteopetrosis, lymphedema, and, more frequently, anhydrotic ectodermal dysplasia, dysmorphic facies, and abnormal conical teeth. The last finding is often helpful in the diagnosis of that condition.
2. Primary Immunodeficiencies of the Adaptive Immune System
a) T cell primary immunodeficiencies. Reticular dysgenesis, a rare severe combined immunodeficiency (SCID) characterized by T lymphopenia and agranulocytosis, can cause sensorineural deafness. Coronin A deficiency is another SCID variant that can be associated with behavioral disorders because the Coronin A gene is located in a genome area known to have been deleted in some patients with this disorder. The lack of enzymes of purine metabolism (adenosine deaminase and purine nucleoside phosphorylase) provokes not only profound T cell lymphocytopenia but also neurologic impairment, including dysautonomia and abnormalities of cognitive development of variable intensity, in many patients. The neurologic impairment can persist after hematopoietic stem cell transplantation (HSCT). Mild chondrodysplasia is a common finding in adenosine deaminase (ADA) deficiency and, indeed, can help the physician arrive at a final diagnosis.