A case study reported that epilepsy-like symptoms led to the misdiagnosis of a Chinese girl with AADC deficiency.
The researchers note that the condition underscores the difficulty of distinguishing between epileptic fits, or seizures, and ocular crisis—a common symptom of AADC deficiency characterized by a fixed, upward gaze of the eye.
They said early and accurate diagnosis can help avoid misdiagnosis and incorrect treatment.
Case Study , “Mimics epileptic eye crisis in a patient with Chinese L-amino acid decarboxylase deficiency: a case report.“in Frontiers in Neuroscience.
AADC deficiency is characterized by decreased AADC enzyme activity due to mutations in both copies of DDC gene. This enzyme deficiency impairs the production of certain neurotransmitters, or signaling molecules that are essential for nerve cell communication, and many aspects of brain activity. Symptoms vary greatly from person to person, mainly due to varying levels of these neurotransmitters.
The main symptoms include low muscle tone at an early age, slow movements, involuntary muscle contraction (dystonia), eye crises, delayed growth, drooping eyelids, and excessive sweating.
An eye crunch is a disorder of the eye movement in which the gaze is involuntarily fixed upward due to spasms of the eye muscles. During a seizure that can last for hours as the disease progresses, the patient is unable to move his eyes.
These seizures are usually accompanied by an open mouth, a protruding tongue, restricted neck movement, and lip smacking – mimicking in many aspects what happens in epileptic seizures.
Less common neurological symptoms include seizures, sleep difficulties, and certain behavioral problems, such as irritability, excessive crying, dysarthria, or a deep state of restlessness or dissatisfaction.
Due to how rare AADC deficiency is – there are only about 120 reported cases – clinical experience with diagnosis and treatment is limited, which can lead to misdiagnosis.
Researchers at Beijing Children’s Hospital in China describe the case of a young girl with AADC deficiency who was misdiagnosed as having epilepsy.
The girl was the second child of healthy parents and pregnancy and childbirth were uneventful. Soon after birth, she showed poor sucking ability and feeding difficulties.
By two and a half months, she began having episodes of shifting her eyes upward or to the right and her arms and legs stiff. At first, it was happening two to three times a month, but it increased to seven to eight times a month. It usually lasted about five minutes, but sometimes lasted up to 30 minutes.
The episodes were caused by crying, tiredness, or infection and were resolved either spontaneously or by relaxation or sleep.
The episodes of ocular deviation worsened after four months, occurred two to three times a day and lasted up to two hours.
The girl was hospitalized assuming she had epilepsy and was treated with antiepileptic medication, which resulted in a limited response.
Further examination revealed she had weak muscles, stiff extremities, severe developmental delays, poor head control – which she lost at the onset of symptoms – and was unable to roll over or follow sounds or objects.
She also showed signs of irritability, excessive crying, difficulty sleeping, dysphonia, drooling, excessive sweating, and drooping eyelids.
Her older brother also showed similar symptoms at 4 months old and was diagnosed with epilepsy and cerebral palsy – a group of disorders that affect movement and muscle tone.
Drug treatment and rehabilitation were ineffective and he died at the age of 10 with the cause of death given by both parents as heart failure and kidney failure. No genetic testing was done on the boy and no other family members were affected.
Genetic testing confirms the diagnosis of AADC
The girl underwent a video-monitoring electroencephalogram (EEG) to measure the electrical activity of her brain before, during and after bouts of ocular deviation. No signs of epilepsy-related brain activity were detected, strongly suggesting that the episodes were instead ocular crises with dystonia.
Analyzes of her blood and cerebrospinal fluid, the fluid surrounding the brain and spinal cord, showed an abnormal neurotransmitter pattern. The activity levels of AADC in the blood were also much lower than normal.
The diagnosis of AADC deficiency was confirmed by genetic testing, which showed a different mutation in each of the two copies of DDC The two genes – one inherited from her mother (419 AD > a) and the other from her father (1375 c > t).
None of the mutations has been described before. Both were classified as variants of uncertain significance, which means that it is unclear whether they led to deleterious changes in the resulting AADC enzyme.
After the diagnosis, the girl received AADC-related treatments, which improved her sleep and reduced the frequency of eye disease episodes to every three to eight days, for one hour.
Follow-up at 18 months showed average body growth with ocular crisis episodes occurring every seven to eight days and lasting up to two hours.
“However, there was no improvement in her developmental delay,” the researchers wrote, adding that she “still lacked head control, voluntary movements, or language.”
“This case underscores the difficulties and necessity of distinguishing between epileptic seizures and ocular crisis seizures in patients with AADCD, as video-electroencephalography can assist in the differential diagnosis,” the researchers wrote. Infants with ocular crisis and dystonia, developmental delays, and [low muscle tone] The AADCD should be considered. “