Aromatic L-amino acid decarboxylase deficiency is a rare

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...

caused by mutations in the '' DDC'' gene, which encodes an enzyme called

aromatic L-amino acid decarboxylase Aromatic L-amino acid decarboxylase (AADC or AAAD), also known as DOPA decarboxylase (DDC), tryptophan decarboxylase, and 5-hydroxytryptophan decarboxylase, is a lyase enzyme (), located in region 7p12.2-p12.1. Mechanism The enzyme uses pyri ...

Signs and symptoms

Biosynthesis and breakdown of serotonin and the catecholamines, and the metabolic block in AADC deficiency

Babies with severe aromatic L-amino acid decarboxylase deficiency usually present during the first few months of life. Symptoms can include: *

Hypotonia Hypotonia is a state of low muscle tone (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases a ...

(floppiness) *

Developmental delay Global developmental delay is an umbrella term used when children are significantly delayed in their cognitive and physical development. It can be diagnosed when a child is delayed in one or more milestones, categorised into motor skills, speech, c ...

Oculogyric crises Oculogyric crisis (OGC) is the name of a dystonic reaction to certain drugs or medical conditions characterized by a prolonged involuntary upward deviation of the eyes. The term "oculogyric" refers to the bilateral elevation of the visual gaze, but ...

* Difficulty with initiating and controlling movements *

Dystonia Dystonia is a neurological hyperkinetic movement disorder in which sustained or repetitive muscle contractions result in twisting and repetitive movements or abnormal fixed postures. The movements may resemble a tremor. Dystonia is often inten ...

and

dyskinesia Dyskinesia refers to a category of movement disorders that are characterized by involuntary muscle movements, including movements similar to tics or chorea and diminished voluntary movements. Dyskinesia can be anything from a slight tremor of t ...

* Gastointestinal dysmotility which can present at as vomiting, gastro-oesophageal reflux, diarrhoea and/or constipation * Autonomic symptoms including difficulties controlling temperature and blood sugar, excessive sweating and nasal congestion Some people may develop

cerebral folate deficiency Cerebral folate deficiency is a condition in which concentrations of 5-methyltetrahydrofolate are low in the brain as measured in the cerebral spinal fluid despite being normal in the blood. Symptoms typically appear at about 5 to 24 months of age ...

, because O-methylation of the excessive amounts of L-Dopa can deplete methyl donors such as

S-adenosyl methionine ''S''-Adenosyl methionine (SAM), also known under the commercial names of SAMe, SAM-e, or AdoMet, is a common cosubstrate involved in methyl group transfers, transsulfuration, and aminopropylation. Although these anabolic reactions occur throug ...

and

levomefolic acid Levomefolic acid (INN, also known as L-5-MTHF, L-methylfolate and L-5-methyltetrahydrofolate and (6''S'')-5-methyltetrahydrofolate, and (6''S'')-5-MTHF) is the primary biologically active form of folate used at the cellular level for DNA reprodu ...

. This deviation can be detected by measuring the levels of levomefolic acid in the

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...

, and can be corrected by

folinic acid Folinic acid, also known as leucovorin, is a medication used to decrease the toxic effects of methotrexate and pyrimethamine. It is also used in combination with 5-fluorouracil to treat colorectal cancer and pancreatic cancer, may be used to tr ...

Genetics

Aromatic L-amino acid decarboxylase deficiency is an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

condition, meaning an individual needs to have two faulty copies of the ''DDC'' gene in order to be affected. Usually, one copy is inherited from each parent.

Pathophysiology

The aromatic L-amino acid decarboxylase deficiency enzyme is involved in the synthesis of

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...

and

serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...

, both of which are important

neurotransmitters A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neur ...

Diagnosis

Once there is a clinical suspicion of the diagnosis, neurotransmitters can be analysed in

from a lumbar puncture. If these show the pattern of abnormalities typical for aromatic L-amino acid decarboxylase deficiency, the diagnosis can be confirmed by genetic testing and/or measurement of

enzyme activity Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition. Enzyme units The quantity or concentration of an enzyme can be expressed in molar amounts, as with any ...

Treatment

There is no cure for aromatic L-amino acid decarboxylase deficiency, but medical and multidisciplinary treatment can relieve some of the symptoms. Individuals will require

physiotherapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patient ...

occupational therapy Occupational therapy (OT) is a global healthcare profession. It involves the use of assessment and intervention to develop, recover, or maintain the meaningful activities, or ''occupations'', of individuals, groups, or communities. The field of ...

, and

speech and language therapy Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...

. Some will need

enteral feeding Enteral administration is food or drug administration via the human gastrointestinal tract. This contrasts with parenteral nutrition or drug administration (Greek ''para'', "besides" + ''enteros''), which occurs from routes outside the GI tract, ...

(for example, a

gastrostomy Gastrostomy is the creation of an artificial external opening into the stomach for nutritional support or gastric decompression. Typically this would include an incision in the patient's epigastrium as part of a formal operation. It can be perfor ...

jejunostomy Jejunostomy is the surgical creation of an opening (stoma) through the skin at the front of the abdomen and the wall of the jejunum (part of the small intestine). It can be performed either endoscopically, or with open surgery. A jejunostomy may ...

) due to difficulties with chewing and swallowing. Various medications can help compensate for the missing neurotransmitters.

Dopamine agonists A dopamine agonist (DA) is a compound that activates dopamine receptors. There are two families of dopamine receptors, D2-like and D1-like, and they are all G protein-coupled receptors. D1- and D5-receptors belong to the D1-like family and the ...

such as

rotigotine Rotigotine, sold under the brand name Neupro among others, is a dopamine agonist of the non-ergoline class of medications indicated for the treatment of Parkinson's disease and restless legs syndrome. It is formulated as a once-daily transdermal ...

pramipexole Pramipexole, sold under the brand Mirapex among others, is medication used to treat Parkinson's disease (PD) and restless legs syndrome (RLS). In Parkinson's disease it may be used alone or together with levodopa. It is taken by mouth. Pramipex ...

and

monoamine oxidase inhibitors Monoamine oxidase inhibitors (MAOIs) are a class of drugs that inhibit the activity of one or both monoamine oxidase enzymes: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). They are best known as effective antidepressants, espec ...

such as

selegiline Selegiline, also known as L-deprenyl and sold under the brand names Eldepryl and Emsam among others, is a medication which is used in the treatment of Parkinson's disease and major depressive disorder. It is provided in the form of a capsule or ...

are commonly used. Individuals may also need to take a range of other medications to control dyskinesia, constipation and other symptoms. In July 2021, results of a small

gene therapy Gene therapy is a medical field which focuses on the genetic modification of cells to produce a therapeutic effect or the treatment of disease by repairing or reconstructing defective genetic material. The first attempt at modifying human DN ...

phase I study reported observation of dopamine restoration on seven participants between 4 and 9 years old. As of May 2022, the

product eladocagene exuparvovec is recommended for approval by the European Commission.

References

External links

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