T-cell immunodeficiency with thymic aplasia (TIDTA) is an autosomal recessive disorder that is often detected at birth through newborn SCID screening with the finding of decreased T-cell receptor excision circles (TRECs). Affected individuals have selective hypo- or aplasia of the thymus, which results in T-cell immunodeficiency due to impaired T-cell development and increased susceptibility to viral infections. The phenotype is similar to T-/B+/NK+ SCID. Some patients may die in childhood; thymus transplantation may be curative (summary by Du et al., 2019).

Immunodeficiency-73A with defective neutrophil chemotaxis and leukocytosis (IMD73A) is an immunologic disorder characterized by onset of recurrent infections in early infancy. Affected infants have periumbilical erythema and later develop skin abscesses and invasive infections. Laboratory studies show leukocytosis, neutrophilia, decreased TRECs, and T-cell abnormalities. Neutrophils showed decreased chemotaxis associated with actin polymerization abnormalities, as well as variably impaired oxidative responses. Hematopoietic stem cell transplant may be curative (summary by Accetta et al., 2011; review by Lougaris et al., 2020). In a review of autosomal forms of chronic granulomatous disease (see 306400 for genetic heterogeneity of CGD), Roos et al. (2021) noted that patients with RAC2 mutations may manifest CGD-like symptoms due to defects in neutrophil NADPH oxidase activity.

Severe combined immunodeficiency (SCID) due to DCLRE1C deficiency is a type of SCID (see this term) characterized by severe and recurrent infections, diarrhea, failure to thrive, and cell sensitivity to ionizing radiation.

Any primary immunodeficiency disease in which the cause of the disease is a mutation in the BCL11B gene.

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.

Any BAFopathy in which the cause of the disease is a mutation in the BCL11B gene.

Infantile T-cell lymphopenia with or without nail dystrophy (TLIND) is an autosomal dominant disorder characterized by decreased numbers of T cells, particularly cytotoxic CD8+ T cells, usually apparent from infancy. Patients are often identified through newborn screening with the finding of low levels of T-cell receptor excision circles (TRECs). Affected individuals tend to be more susceptible to recurrent infections, mainly respiratory viral infections. However, the severity is highly variable, and patients usually improve with age later in childhood and as adults, even if CD8+ T cells remain decreased compared to normal. Additional features may include a small thymic shadow, indicative of impaired thymic development, skin abnormalities, such as atopic dermatitis, and nail dystrophy. As rare patients may develop more serious infections, affected individuals should be monitored. Bone marrow transplantation is not curative (summary by Bosticardo et al., 2019).

Immunodeficiency-73B with defective neutrophil chemotaxis (IMD73B) is an autosomal dominant immunologic disorder characterized by onset of recurrent infections in infancy or early childhood. Affected individuals develop respiratory infections, cellulitis, and severe invasive infections or sepsis; organisms include bacteria such as Staphylococcus, as well as viruses, fungi, and mycobacterial species. Laboratory studies show variable abnormalities, including B- and T-cell lymphopenia, decreased immunoglobulin subsets, decreased TRECs and dysfunctional T cells, decreased NK cells, neutropenia, and impaired neutrophil chemotaxis. Hematopoietic stem cell transplantation is curative (summary by Hsu et al., 2019; review by Lougaris et al., 2020). In a review of autosomal forms of chronic granulomatous disease (see 306400 for genetic heterogeneity of CGD), Roos et al. (2021) noted that patients with RAC2 mutations may manifest CGD-like symptoms due to defects in neutrophil NADPH oxidase activity.

Immunodeficiency-81 (IMD81) is an autosomal recessive complex immunologic disorder with onset of symptoms in infancy. The phenotype is highly variable and may include both immunodeficiency with recurrent infections, including bacterial and fungal infections, as well as autoimmune features, including autoimmune hemolytic anemia, pancytopenia, thrombocytopenia, and inflammatory bowel disease. Immunologic workup shows immune dysregulation with abnormalities affecting multiple immune cell lineages, including T cells, B cells, NK cells, and neutrophils, which may be decreased or increased and demonstrate functional deficits. There is a wide range of hematologic abnormalities. Affected individuals may be susceptible to severe EBV infection. The disorder is caused by a defect in intracellular immune signaling pathways (summary by Lev et al., 2021; Edwards et al., 2023).

Dyskeratosis congenita and related telomere biology disorders (DC/TBD) are caused by impaired telomere maintenance resulting in short or very short telomeres. The phenotypic spectrum of telomere biology disorders is broad and includes individuals with classic dyskeratosis congenita (DC) as well as those with very short telomeres and an isolated physical finding. Classic DC is characterized by a triad of dysplastic nails, lacy reticular pigmentation of the upper chest and/or neck, and oral leukoplakia, although this may not be present in all individuals. People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis. Other findings can include eye abnormalities (epiphora, blepharitis, sparse eyelashes, ectropion, entropion, trichiasis), taurodontism, liver disease, gastrointestinal telangiectasias, and avascular necrosis of the hips or shoulders. Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms; additional findings include cerebellar hypoplasia (Hoyeraal Hreidarsson syndrome) and bilateral exudative retinopathy and intracranial calcifications (Revesz syndrome and Coats plus syndrome). Onset and progression of manifestations of DC/TBD vary: at the mild end of the spectrum are those who have only minimal physical findings with normal bone marrow function, and at the severe end are those who have the diagnostic triad and early-onset BMF.