MedGen

Reduced level of T cell receptor excision circle (TRECs) as measured by the TREC assay. Late in maturation, 70% of thymocytes that will ultimately express alpha/beta-T cell receptors form a circular DNA TREC from the excised TCRdelta gene that lies within the TCRalpha genetic locus. The circles are stable but do not increase following cell division and, therefore, become diluted as T cells proliferate. A quantitative polymerase chain reaction (PCR) reaction across the joint of the circular DNA provides the TREC copy number, a marker of newly-formed, antigenically-naïve thymic emigrant T cells. [from HPO]

An anomaly of the circle of Willis, also known as the cerebral arterial circle. [from HPO]

MHC class II deficiency-4 (MHC2D4) is an autosomal recessive immunodeficiency characterized by the onset of recurrent, persistent infections from birth, resulting in failure to thrive. Infectious agents include bacteria, viruses, fungi, and protozoa, usually affecting the respiratory and gastrointestinal tract. Laboratory studies show decreased CD4+ T cells, hypogammaglobulinemia, an inverted CD4:CD8 ratio, and absence of MHC type II antigens (HLA-DR, -DQ, and DP) on the surface of antigen-presenting cells. Expression of MHC type I antigens may also be decreased (referred to as 'BLS type III'). Patients may die in infancy or early childhood, unless they undergo bone marrow transplantation, which can be curative, although complications are common. MHC2D4 may not be detected by newborn T-cell receptor excision circle (TREC) screening (summary by Mousavi Khorshidi et al., 2023). For a discussion of genetic heterogeneity of MHC class II deficiency, see MHC2D1 (209920). [from OMIM]

MHC class II deficiency-3 (MHC2D3) is a rare autosomal recessive immunodeficiency characterized by the onset of recurrent and persistent infections from birth. Infectious agents include bacteria, viruses, fungi, and protozoa, usually affecting the respiratory and gastrointestinal tract. Laboratory studies show decreased CD4+ T cells, hypogammaglobulinemia, an inverted CD4:CD8 ratio, and absence of MHC type II antigens (HLA-DR, -DQ, and -DP) on the surface of antigen-presenting cells. Most patients die in infancy or early childhood unless they undergo bone marrow transplantation, which can be curative, although complications are common. Rare patients may survive longer, even without bone marrow transplant. MHC class II deficiency may not be detected by newborn T-cell receptor excision circle (TREC) screening (summary by El Hawary et al., 2019; Mousavi Khorshidi et al., 2023). For a discussion of genetic heterogeneity of MHC class II deficiency, see MHC2D1 (209920). [from OMIM]

Hyper-IgE syndrome-6 with recurrent infections (HIES6) is an autosomal dominant immunologic disorder characterized by early-childhood onset of severe refractory atopic dermatitis, IgE-mediated food and drug allergies, asthma, and eosinophilic esophagitis. Laboratory studies show increased serum IgE levels and eosinophilia. Affected individuals are susceptible to life-threatening anaphylaxis. Additional features may include allergic rhinitis, recurrent secondary infections (bacterial, viral, fungal), and short stature. Rare patients show intracerebral vascular abnormalities, including the Circle of Willis, increased risk of ruptured aneurysm, and B-cell lymphoma. The disorder results from immune dysregulation with inappropriate activation of inflammatory signaling pathways associated with a Th2 phenotype. Treatment with an IL4 (147780)/IL13 (147683) inhibitor (dupilumab) or JAK inhibitor results in clinical improvement. Sharma et al. (2023) classified this disease as a 'primary atopic disorder' (PAD). For a discussion of genetic heterogeneity of hyper-IgE syndrome, see HIES1 (147060). [from OMIM]

A noninflammatory, progressive occlusion of the intracranial carotid arteries owing to the formation of netlike collateral arteries arising from the circle of Willis. [from HPO]

A syndrome which occurs as a result of the occlusion of one of the vertebral arteries. It may be caused by atherosclerosis, embolism or hemorrhage. Collateral circulation through the circle of Willis is usually comprised as well. Clinical signs may include vertigo, nystagmus, dysarthria, ataxia and sensorimotor deficits. Clinical course may lead to persistence of neurologic deficits. Prognosis is variable with a substantial risk for recurrent infarction. [from MONDO]

An uncommon neurovascular condition seen with exertion of the upper extremity. It is usually caused by atherosclerotic stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery. In order to maintain adequate perfusion of the arm during exercise on the affected side, the narrowed subclavian artery siphons off retrograde blood flow from the ipsilateral vertebral artery. This is possible due to lower blood pressure distal to the site of narrowing and collateral circulation through the circle of Willis. Affected individuals may remain asymptomatic until the oxygen demand generated from upper extremity exercise requires a large enough compensatory volume of blood to be diverted from the vertebral artery to provoke vertebrobasilar insufficiency and its accompanying neurological sequelae. Presenting clinical signs may include pain or numbness of the affected arm (with diminished pulses and a brachial systolic blood pressure differential of greater than 20 mmHg as compared to the opposite arm), vertigo, tinnitus, dysarthria, diplopia and syncope. Notably, unlike cerebral infarction, the clinical course does not lead to chronic neurologic disability. Prognosis for recovery of normal anterograde circulation is favorable following endovascular or surgical intervention. [from NCI]

The subclavian artery arises from ductus arteriosus. While the ductus arteriosus is patent its blood supply comes from the ductus, hence from the pulmonary artery. After it closes, the blood supply is retrogradely from the vertebral artery via the circle of Willis. [from HPO]