chemistry

Succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase deficiency is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Succinic semialdehyde dehydrogenase deficiency rather than just read about it. In short: Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive disorder of the degradation pathway of the inhibitory neurotransmitter γ-aminobutyric acid, or GABA. The disorder has been identified in approximately 350 families, with a significant proportion being consanguineous families.

Key takeaways

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Reference excerpt

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive disorder of the degradation pathway of the inhibitory neurotransmitter γ-aminobutyric acid, or GABA. The disorder has been identified in approximately 350 families, with a significant proportion being consanguineous families. The first case was identified in 1981 and published in a Dutch clinical chemistry journal that highlighted a number of neurological conditions such as delayed intellectual, motor, speech, and language as the most common manifestations. Later cases reported in the early 1990s began to show that hypotonia, hyporeflexia, seizures, and a nonprogressive ataxia were frequent clinical features as well. SSADH deficiency is caused by an enzyme deficiency in GABA degradation. Under normal conditions, SSADH works with the enzyme GABA transaminase to convert GABA to succinic acid. Succinic acid can then be utilized for energy production via the Krebs cycle. However, because of the deficiency, the final intermediate of the GABA degradation pathway, succinic semialdehyde, accumulates and cannot be oxidized to succinic acid and is therefore reduced to gamma-hydroxybutyric acid (GHB) by gamma-hydroxybutyric dehydrogenase. This causes elevations in GHB and is believed to be the trademark of this disorder and cause for the neurological manifestations seen.

Signs and symptoms The symptoms of SSADH deficiency fall into three primary categories: neurological, psychiatric, and ocular. The most constant features seen are developmental delay, hypotonia and intellectual disability. Nearly half of patients seen manifest ataxia, behavior problems, seizures, and hyporeflexia. The age of onset ranges from newborn period to 25 years. Problems unique to neonates can include prematurity, lethargy, decreased sucking, respiratory difficulty and hypoglycemia. Gastrointestinal symptoms have been seen primarily in this population and are usually related to increased feeding. Ocular problems related to the disorder include strabismus, nystagmus, retinitis, disc pallor, and oculomotor apraxia. Over half of the patients with SSADH deficiency have seizures. These include absence, tonic clonic, and convulsive status epilepticus. It is unclear whether decreased levels of GABA or elevated levels of GHB are responsible for these seizures but alterations in these neurotransmitters and their receptor binding or neurotransmitter transport is hypothesized to play a role in the pathogenesis of the seizures in this population. Symptoms associated with SSADHD may be mild, moderate or severe and often vary greatly from case to case. The symptoms of SSADH are caused by the accumulation of GHB in the brain and include the following manifestations (Defined as: common, > 70% of patients; frequent 30-70% of patients;unusual, < 30% of patients): Common manifestations include:

Delayed gross motor development Delayed mental development Delayed fine motor skill development Delayed speech and language development Hypotonia Frequent manifestations include:

Seizures Hyporeflexia Ataxia Behavioral problems Hyperkinesis Unusual manifestations include:

Neonatal problems EEG abnormalities Psychoses MRI or X-ray computed tomography abnormalities Oculomotor apraxia Microcephaly Macrocephaly Hyperreflexia Somnolence Choreoathetosis Myopathy

Genetics

SSADH deficiency is inherited in an autosomal recessive fashion. Such diseases are caused by an error in a single DNA gene. Because the disease is autosomal, the defective gene is found on an autosome (chromosome 6), rather than the sex-linked 23rd chromosome. Being a recessive disorder, the disease can only be inherited from both parents since the disorder can only occur when a person has two copies of the gene. It is believed that the genetic basis for SSADH deficiency resides in the SSADH human ALDH5A1 gene, which maps to chromosome 6p22. More than 47 disease-causing mutations have been identified for the disorder, all of which lead to absence of functional proteins through missense, nonsense, or splicing errors; no hotspots have been identified. Consanguinity is frequent; this suggests the rare occurrence of disease-causing alleles in the general population.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Succinic semialdehyde dehydrogenase deficiency

Start with the simplest possible case. Write down what Succinic semialdehyde dehydrogenase deficiency claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Succinic semialdehyde dehydrogenase deficiency before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Succinic semialdehyde dehydrogenase deficiency ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Succinic semialdehyde dehydrogenase deficiency

In research: Succinic semialdehyde dehydrogenase deficiency appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Succinic semialdehyde dehydrogenase deficiency in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Succinic semialdehyde dehydrogenase deficiency is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amino acid metabolism disorders, Autosomal recessive disorders, Rare diseases, so understanding it makes those chapters shorter.
In everyday life: Look for Succinic semialdehyde dehydrogenase deficiency outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Succinic semialdehyde dehydrogenase deficiency in 20 minutes

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Frequently asked questions

What is Succinic semialdehyde dehydrogenase deficiency in simple terms?

Why does Succinic semialdehyde dehydrogenase deficiency matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Succinic semialdehyde dehydrogenase deficiency?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Succinic semialdehyde dehydrogenase deficiency.