Adenylosuccinase deficiency

Other Names: Adenylosuccinate lyase deficiency; ADSL deficiency

Adenylosuccinase deficiency impacts the way the body breaks down certain chemicals and results in damage to the nervous system. It is a neurological disorder that causes brain dysfunction (encephalopathy) leading to delayed development of mental and movement abilities (psychomotor delay), autistic behaviors that affect communication and social interaction, and seizures.

Types

There are several types of adenylosuccinase deficiency.

• The most severe is the neonatal form.
• Adenylosuccinate lyase deficiency type I (also known as the severe form) is the most common.
• In individuals with adenylosuccinate lyase deficiency type II (also known as the moderate or mild form), development is typically normal for the first few years of life but then slows.

Epidemiology

Adenylosuccinate lyase deficiency is a rare disorder; fewer than 100 cases have been reported. The condition is most common in the Netherlands and Belgium, but it has been found worldwide.

Cause

All forms of adenylosuccinate lyase deficiency are caused by mutations in the ADSL gene. This gene provides instructions for making an enzyme called adenylosuccinate lyase, which performs two steps in the process that produces purine nucleotides. These nucleotides are building blocks of DNA, its chemical cousin RNA, and molecules such as ATP that serve as energy sources in the cell.

Adenylosuccinate lyase converts a molecule called succinylaminoimidazole carboxamide ribotide (SAICAR) to aminoimidazole carboxamide ribotide (AICAR) and converts succinyladenosine monophosphate (SAMP) to adenosine monophosphate (AMP). Most of the mutations involved in adenylosuccinate lyase deficiency change single protein building blocks (amino acids) in the adenylosuccinate lyase enzyme, which impairs its function. Reduced function of this enzyme leads to buildup of SAICAR and SAMP, which are converted through a different reaction to succinylaminoimidazole carboxamide riboside (SAICAr) and succinyladenosine (S-Ado). Researchers believe that SAICAr and S-Ado are toxic; damage to brain tissue caused by one or both of these substances likely underlies the neurological problems that occur in adenylosuccinate lyase deficiency.

Studies suggest that the amount of SAICAr relative to S-Ado reflects the severity of adenylosuccinate lyase deficiency. Individuals with more SAICAr than S-Ado have more severe encephalopathy and psychomotor delay.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

The following list includes the most common signs and symptoms in people with adenylosuccinase deficiency. These features may be different from person to person. Some people may have more symptoms than others and symptoms can range from mild to severe. This list does not include every symptom or feature that has been described in this condition.

Signs and symptoms include:

• Intellectual disability
• Severe motor delay
• Seizures
• Low muscle tone
• Autistic behaviors

Symptoms of adenylosuccinase deficiency tend to get worse over time. There are three types of adenylosuccinase deficiency. The most severe form is the fatal neonatal form in which symptoms are present in infancy. In the other forms, symptoms begin later in childhood. Less than 100 people have been reported with this condition and the severity of symptoms is different from person to person.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

• Abnormal facial shape(Unusual facial appearance)
• Absent speech(Absent speech development)
• Anteverted nares(Nasal tip, upturned)
• Brachycephaly(Short and broad skull)
• Flat occiput
• Generalized hypotonia(Decreased muscle tone)
• Hypointensity of cerebral white matter on MRI
• Intellectual disability(Mental deficiency)
• Long philtrum
• Low-set ears(Low set ears)
• Microcephaly(Small head circumference)
• Prominent metopic ridge
• Seizure
• Severe global developmental delay
• Short nose(Decreased length of nose)
• Smooth philtrum
• Thin upper lip vermilion(Thin upper lip)

5%-29% of people have these symptoms

• Happy demeanor

Diagnosis

Adenylosuccinase deficiency is diagnosed through a clinical exam, imaging studies, laboratory tests, and confirmed by genetic testing. People with this condition have two unusual chemicals present in the cerebral spinal fluid, urine and plasma.

Treatment

Treatment of adenylosuccinate deficiency is focused on managing the symptoms.

Treatment of adenylosuccinate lyase deficiency can be done via epilepsy management with anticonvulsive drugs. Additionally the following options include:

• S-adenosylmethionine
• D-ribose and uridine administration
• Ketogenic diet
• S-adenosyl-l-methionine

Specialists involved in the care of someone with adenylosuccinate deficiency may include:

• Neurologist
• Neonatologist
• Radiologist

NIH genetic and rare disease info

• NIH info on Adenylosuccinase deficiency

Adenylosuccinase deficiency is a rare disease.

Adenylosuccinase deficiency Resources
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