Keywords DADA2 - fast-track exome sequencing - inflammation - vasculitis - brainstem - early
stroke
Introduction
Deficiency of adenosine deaminase 2 (DADA2) is a rare Mendelian, autoinflammatory
multiorgan disease inherited in an autosomal recessive manner. It was first described
in 2014.[1 ] Loss-of-function mutations in the ADA2 gene (formerly called CECR1 ) lead to a deficiency of the enzyme adenosine deaminase 2 (ADA2), which has complex
immunological functions and is also a growth factor.[2 ]
[3 ] The frequency of pathogenic variants is approximately 1:1,000 or lower.[4 ]
[5 ] Jee et al[6 ] revealed an estimated carrier frequency of at least 1 in 236 individuals, corresponding
to an expected DADA2 disease prevalence of 1:222,000 individuals. Penetrance is incomplete.
There is no clear genotype-phenotype correlation and the phenotype varies widely even
within a family.[3 ]
[7 ] Most patients present clinical symptoms in the first decade of life and can have
a variety of different symptoms with underlying vasculopathy and inflammation, bone
marrow failure, or immunodeficiency with overlapping phenotypes. Vasculitis of the
small and medium-sized arteries leads to the neurologically predominant symptoms of
DADA2. Lacunar ischemic infarcts in the deep-brain nuclei, midbrain, and/or brainstem
are very typical.[8 ]
[9 ] Strokes occur in about one-third of the patients, often in early childhood and may
recur and leading to serious residual damage.[10 ] Since other organs might also be affected by vasculitis and inflammation, the possible
clinical symptoms are multifaceted. In addition, hematologic symptoms could occur
and immunodeficiency may develop.[3 ]
Treatment with tumor necrosis factor (TNF) blockers (etanercept, adalimumab, infliximab)
has been well established.[8 ]
[11 ] Stem cell transplantation is a therapeutic modality in hematologic manifestations
and severe combined immunodeficiency.[3 ] Gene therapy may also be a treatment option for young patients in the future.[12 ]
Case
We presented the case of a 3 years and 8 months old girl child patient with DADA2
([Table 1 ]). The child's previous medical history was unremarkable except for thrombocytopenia
(28 Tsd/µL) in the neonatal period. She received a platelet concentrate on the first
day of life. Further on, the platelets were in the low-normal reference range. The
parents were not consanguine and both were healthy, as well as the older sister.
Table 1
Tabular listing of the symptoms of our patient
Acute clinical presentation at 3.8 years of age
Oculomotor nerve palsy right, central facial nerve palsy left, hemiataxia left
Medical history
Thrombocytopenia (28 thousand/µL) at the first day postpartum, otherwise healthy,
no special conditions
Genetic findings
Compound heterozygous variants: paternally inherited Chr22:17690409-17690410; NM_001282225.2:c.158del;
p.(Asn53Thrfs*12) probably pathogenic (PVS1, PM2_SUP) and maternally inherited chr22:17690566;
NM_001282225.2:c.2T > A, p.0? variant of unclear significance (PVS1_SUP, PM2_SUP,
PM3 MOD)
ADA2 enzymatic activity
0,0 mU/g protein in plasma
MRI
Mesencephalic lesion
Vasculitis
Apart from brainstem stroke, no other symptoms
Immunology
IgA deficiency (0.26 g/L), IgM deficiency (0.12 g/L)
(normalized 10 months after starting adalimumab: IgA 0.98 g/L, IgM 0.31 g/L)
Pathological inflammation parameters
CRP 10.38 mg/L, IL-2 receptor 1370.0 U/mL, SAA 23.3 mg/L, ferritin 94.8 ng/mL, strong
type 1 interferon activation in the blood
Immunophenotyping
Th17-like cells marginally decreased, also in the controls under adalimumab. Otherwise
normal number and distribution of lymphocytes, monocytes, and granulocytes, as well
as T and NK cells
B cell differentiation
Slightly decreased naive and memory B cells with otherwise normal population distribution
T cell differentiation
Age-appropriate distribution and activation pattern of the measured subpopulations
Vaccination titers
Present for the tested titers (measles, varicella, hepatitis B, tetanus, and diphtheria)
Hematology
Mild hypoplasia of erythropoiesis in bone marrow smear with unremarkable peripheral
blood smear
Cerebrospinal fluid
Oligoclonal bands positive
Abbreviations: ADA2, adenosine deaminase 2; CRP, C-reactive protein; Ig, immunoglobulin;
IL, interleukin; MRI, magnetic resonance imaging; SAA, serum amyloid A.
Without any prodromal symptoms the girl developed right-sided oculomotor nerve paresis
([Fig. 1 ]), left-sided central facial paresis, and left-sided hemiataxia. She also was somnolent
and irritable. Two hours after the onset of symptoms, she was brought to the hospital
and an acute brainstem pathology was diagnosed. Emergency magnetic resonance imaging
(MRI) of the brain showed a diffusion-weighted imaging lesion on the right side of
the midbrain with a decrease in apparent diffusion coefficient (ADC), indicative of
cytotoxic edema. In the beginning, this can be seen in inflammatory (infectious and
demyelinating), as well as ischemic lesions. Vasogenic edema with increased ADC may
then come later ([Fig. 2 ]). It was difficult to differentiate whether this was a local ischemia or an inflammatory
process. Given the likelihood in early childhood, we had tended to favor inflammation
and treated accordingly. We decided against thrombolysis and in favor of high-dose
treatment with intravenous methylprednisolone (20 mg/kg) for 5 days. Due to delayed
improvement immunoglobulins (2 g/kg over 2 days) were administered secondly because
of the possibility of Bickerstaff encephalitis. When steroids and immunoglobulins
failed to produce a therapeutic breakthrough and MRI on day 10 showed demarcation
in midbrain, we considered it to be occlusion of the small arteries. The patient subsequently
received acetylsalicylic acid (ASA) for secondary stroke prophylaxis. The initial
diagnostic tests did not show any anomalies, apart from detectable oligoclonal bands
in the cerebrospinal fluid. Subsequent genetic testing revealed the cause. Single
exome sequencing identified two compound heterozygous variants in the ADA2 gene: the likely pathogenic variant c.158del, p.(Asn53Thrfs*12) based on the American
College of Medical Genetics and Genomics criteria[13 ] and the variant of unknown significance (VUS) variant c.2T > A, p.(0?). Compound
heterozygosity could be determined from single exome sequencing due to the close proximity
of the variants ([Supplementary Fig. S1 ], available in the online version only). The extended diagnostic workup revealed
a severe deficiency of plasma ADA2 enzyme activity of 0.0 mU/g protein, as measured
in extracts of dried plasma spots as described in Ben-Ami et al.[14 ] The patient also had immunoglobulin (Ig) A (0.26 g/L) and IgM (0.12 g/L) deficiency,
slightly decreased low naive and memory B cells (consistent with IgM deficiency) and
slightly decreased Th17 lymphocytes, and a strong type 1 interferon activation in
the blood. Bone marrow biopsy showed mild hypoplasia of erythropoiesis.
Fig. 1 Patient 1 week after stroke: the picture shows the ipsilateral oculomotor nerve palsy
on the right (gaze down and out, dilated pupil).
Fig. 2 Magnetic resonance imaging (MRI) of the patient's brain: Circumscribed small diffusion
disturbance in the right cerebral peduncle on day 1 is demonstrated in (A1 ) (diffusion-weighted imaging [DWI]) and (A2 ) (apparent diffusion coefficient [ADC]). In (B ), demarcation of the previously diffusion-disturbed lesion on day 10 in fluid-attenuated
inversion recovery (FLAIR) is shown. In (C ), there is almost complete regression of the finding on day 72 in FLAIR.
Based on the ADA2 deficiency in plasma, DADA2 from the vasculitis phenotype was confirmed.
In light of this new information, the VUS in the ADA2 gene could be reclassified as
pathogenic and the likely pathogenic variant elevated to pathogenic. TNF-blocker treatment
with adalimumab was started. Prophylaxis with ASA was stopped, because antiplatelet
agents are known to increase the risk of hemorrhagic stroke in DADA2.[3 ]
[16 ]
[17 ] After a 18-month follow-up period, the patient is symptom-free except for the residual
oculomotor nerve palsy, which has improved only slightly. Further MRI examinations
provided no new abnormalities.
Discussion
Lacunar subcortical stroke in early childhood and brainstem stroke in particular is
suspicious of DADA2. It can be diagnosed in the case of compound heterozygosity by
genetic testing and, alternatively, by enzymatic confirmation of ADA2 deficiency.
With our case report, we hope to raise awareness of this quite recently described
disease.[1 ] Skin manifestations (e.g., livedo racemosa, erythema nodosum), as reported in the
majority of patients with DADA2, were not present in our patient. We report on our
patient's neurological symptoms, which initially appeared to be isolated. In the early
stage, it was difficult to differentiate between an ischemic and inflammatory process
in the brainstem on the basis of the MRI. ADA2 deficiency leads to reduced vascular
integrity and perivascular inflammation by proinflammatory cytokines (TNF and interleukin-1β)
and subsequently to lacunar ischemic strokes. It is probably a mixed picture due to
the underlying pathophysiology. Detection of oligoclonal bands in cerebral spinal
fluid indicated chronic central nervous system inflammation.
Neurological symptoms can precede other organ manifestations in DADA2.[15 ] We would like to highlight this. In the more detailed workup, immunological abnormalities
also were revealed but had to be specifically searched for in an almost uneventful
medical history of our patient. We believe that thrombocytopenia in the neonatal period
can be retrospectively considered as the first symptom of the disease. However, it
did not play any further role in our patient.
The diagnosis of DADA2 has therapeutic implications.[3 ]
[16 ]
[17 ] If DADA2 is diagnosed at an early stage, treatment can be initiated quickly, complications
avoided, and outcomes improved. There is wide agreement that treatment with TNF blockers
is indicated in the vasculitis phenotype and stem cell transplantation is necessary
for patients with severe immunodeficiency in DADA2. However, clinically relevant questions
remain open. We believe a patient registry is necessary to find yet unanswered questions,
assess long-term outcomes, and optimize patient care.
Early stroke always needs a thorough search for various possible underlying causes.
This case is a striking example how today's genetic diagnostics can lead to early
diagnosis in rare diseases. If the cause cannot be clearly determined and several
genetic and metabolic diseases are considered, fast-track genetic diagnostics with
exome sequencing should be part of the workup of childhood stroke to capture a broad
spectrum of differential diagnoses. If DADA2 is suspected, targeted measurement of
ADA2 activity in plasma may provide a fast result. Should an ADA2 deficiency be detected,
in a second step, however, genetic confirmation diagnostics should then follow.
Conclusion
Strokes of unexplained etiology in the first decade of life and especially lacunar
and brainstem infarcts should include testing for DADA2.
