Childhood-Onset Recurrent Ischemic Stroke and Seizure are Associated with Mutation in the Adenosine Deaminase Type 2 Gene

Dear Editor,

Deficiency in adenosine deaminase type 2 (DADA2) is an autosomal recessive disease caused by loss-of-function mutations in the ADA2 gene, first reported in 2014.[1] This monogenic vasculopathy, or vasculitis, most commonly affects infants and young children, closely resembling polyarteritis nodosa.[2] The most prominent symptoms include skin rash and ischemic or hemorrhagic stroke.[3] However, the clinical spectrum continues to expand. Several autoinflammatory, immunological, and hematological manifestations are now well recognized in ADA2 deficiency. The disease exhibits considerable variability, ranging from mild and intermittent symptoms to severe vasculitis and hematological abnormalities. In India, approximately half of the cases in a series exhibited adult-onset disease.[4] Clinical features vary widely, from mild symptoms such as fever and skin rash to severe manifestations, including early-onset stroke and fatal vasculitis. There is considerable phenotypic variability even among patients with the same mutation.[5,6] The pathogenesis of the disease remains poorly understood. The decrease in ADA2 enzyme leads to increased extracellular adenosine levels, which trigger a proinflammatory cascade.[5]

Here, we report a 25-year-old lady, born to a consanguineous marriage between second-degree relatives (the mother having gestational diabetes), with no family history of known medical illnesses and a normal birth and developmental history. She was admitted to our institute with the chief complaint of severe low back pain lasting 5 days before admission, which was associated with hyperacute-onset paraparesis, urinary retention, and a dorsal sensory level, along with several medical complications since childhood, which are summarized here. She had a prolonged febrile episode at the age of 2–6 months, during which detailed evaluations did not reveal any specific infectious, immune, or neoplastic etiology. This was managed conservatively without a specific diagnosis. At the age of 4 years, she experienced arthralgia involving her left wrist and left shoulder, along with fever lasting nearly 3 months. This was diagnosed as reactive arthritis. At the age of 5, she developed an acute onset of binocular double vision, which was postulated to be due to a stroke; however, neuroimaging was negative (Magnetic Resonance Imaging [MRI] brain was normal), and her symptoms improved within days. She had a similar episode with a midbrain infarct evident on imaging at the age of 11 years, and no specific cause was found upon evaluation at that time. At the age of 13, she had an acute onset of left hemiparesis, with a capsular infarct seen on MRI. At the age of 17, she experienced two episodes of seizures accompanied by altered sensorium and headache, again without a specific cause. At 19 years of age, the patient developed transfusion-dependent anemia characterized by reticulocytopenia and was diagnosed with pure red cell aplasia. Complete blood count revealed: hemoglobin, 6.0 g/dL; red blood cell (RBC) count, 2.80 million/cumm; packed cell volume, 23.4%; mean corpuscular volume, 83.6 fL; mean corpuscular hemoglobin, 29.8 pg; mean corpuscular hemoglobin concentration, 36.5%; red cell distribution width, 15.4%; total white blood cells (WBC) count, 5200/cumm; differential count: neutrophils 64%, lymphocytes 27%, monocytes 9%, eosinophils 0%, basophils 0%; platelet count: 188,000/cumm. The neurological evaluation at that time showed mild weakness and spasticity in the lower limbs, brisk deep tendon reflexes (DTR), and upgoing plantar responses. Finally, the patient was admitted to our institute at 25 years of age with hyperacute-onset paraparesis, urinary retention, and a dorsal sensory level, which led to the diagnosis of dorsal myelopathy due to spinal infarct. On examination, she was afebrile, with left-sided pulsation feeble and difficult to palpate; conscious and oriented; impaired complex calculations; bilateral equal and reactive pupillary reaction; left lower motor neuron palsy; normal motor bulk with left-sided hypotonia (Power: Right -5/5; Left Upper Limb (LUL) – 3/5; Left Lower Limb (LLL) – 4/5; DTRs – left 1+, right 2+; bilateral plantars extensors). Meanwhile, her investigations, including prothrombotic state (including Protein C and S deficiency, homocysteine level, and coagulation profile), vasculitis (Antinuclear Antibody [ANA], ds-DNA, Erythrocyte Sedimentation Rate (ESR), and rheumatoid factor), and infectious etiologies (hepatitis B, Human Immunodeficiency Virus (HIV) I and II, and anti-Hepatitis-C virus [HCV]), were unremarkable. However, inflammatory markers were elevated, with CRP at 101.24 mg/L and ESR at 60 mm/h. A 2-Dimensional (2-D) echocardiogram showed concentric left ventricular hypertrophy with preserved systolic function (ejection fraction – 65%).

The patient had been admitted to different institutes in India at various times and had been extensively evaluated for Central Nervous System (CNS) vasculitis—acquired or inherited—hereditary vasculopathies, and mitochondrial disease, but nothing was found. We considered the presence of fever, joint pains, multiple lacunar infarctions in both the anterior and posterior circulation, and pure red cell aplasia. This constellation of symptoms suggested an autoinflammatory syndrome. The patient also has recurrent, painful, reddish papular lesions involving both legs below the knee joint without any ulceration for the last 7–8 years. The presence of purely lacunar infarcts indicated a possible DADA2, a recently described condition. Ultimately, the patient was treated with the Tumor Necrosis Factor (TNF)- α inhibitor adalimumab (40 mg subcutaneously per month) and responded well on follow-up. Concurrently, supportive care with physiotherapy and other neurorehabilitation was initiated. Regular monitoring will continue to ascertain the nature of the disease and the effect of therapy on this patient.

Whole exome sequencing (WES) indicated that the region encompassing exon 2 of the ADA2 gene was not included in the sequencing data, potentially due to a homozygous deletion of exon 2 in the ADA2 gene. To validate our WES data, Polymerase Chain Reaction (PCR) amplification of the exon 2 and exon 3 regions of the ADA2 gene was conducted in the proband and her unaffected parents [Figure 1a]. Our genetic analysis revealed the absence of a 500 bp PCR-amplified product (exon 2) and the presence of a 392 bp PCR product (exon 3) in the proband [Figure 1b], confirming the homozygous deletion of exon 2 of the ADA2 gene. The homozygous deletion in exon 2 of the ADA2 gene can lead to the loss of protein function, resulting in a deficiency of ADA2. Among the plethora of mutations, missense mutations are the most common (about 80%), while copy number variations, including single or multiple exon insertions or deletions in the ADA2 gene, particularly in exon 2, are less frequent, accounting for about 15.87% of the reported mutations.[7,8] To the best of our knowledge, this is the first case report from West Bengal describing a homozygous exon 2 deletion mutation in the ADA2 gene in a patient presenting with recurrent childhood ischemic strokes accompanied by seizures. Most patients present with significant overlap among three major phenotypes: inflammatory/vascular, immune dysregulatory, and hematologic.[9] The present case exhibited vascular and hematological manifestations, such as stroke and pure RBC aplasia.

Figure 1.

Screening of exon 2 deletion in the ADA2 gene in a child affected with adenosine deaminase 2 deficiency. (a). The upper panel represents a two-generation pedigree showing the age and gender of each individual. Filled symbols indicate a symptomatic ADA2 gene mutant individual, and a half-filled symbol indicates an autosomal carrier. (b). PCR was performed using genomic DNA of the affected proband (II-1) and their obligate carrier father (I-1) and mother (I-2) for amplification of the ADA2 gene exons. The PCR products were analyzed on a 7% polyacrylamide gel. Exon 2 and exon 3 of the unaffected father (I-1), mother (I-2), and control (C) could be amplified; no PCR products were detected for exon 2 of the proband (II-1), but exon 3 was successfully amplified. ADA2: adenosine deaminase type 2, PCR: Polymerase Chain Reaction

Our patient finally received a diagnosis after a prolonged diagnostic odyssey, which led to an actionable therapeutic intervention using a TNF- α inhibitor. An earlier diagnosis would likely have prevented the recurrent strokes that the patient has experienced to date. We believe our work will contribute to faster diagnoses and possibly better future patient outcomes, highlighting the importance of genetics in the accurate diagnosis of complex and rare diseases.

In summary, we report a 25-year-old lady presenting with recurrent ischemic stroke associated with seizures, diagnosed with DADA2 through genetic testing. The patient responded well to treatment with the TNF-α inhibitor. This case underscores the importance of considering DADA2 in the differential diagnosis of pediatric or young-onset recurrent strokes, particularly when accompanied by systemic features. Early and accurate diagnosis, followed by appropriate immunosuppressive therapy, can significantly reduce morbidity and prevent further disease progression.

Declaration of patient consent

The authors declare that they have obtained all appropriate patient consent forms to publish clinical and genetic data, ensuring confidentiality and adherence to ethical standards. The patient understands that her name and initials will not be published, and due efforts will be made to conceal her identity; however, anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

This work was supported by grants from the Department of Science and Technology and Biotechnology, Government of West Bengal (STBT-11012 (19)/15/2024-ST SEC), and Department of Biotechnology, Ministry of Science and Technology, Government of India (BT/NIDAN/01/05/2018).