HSD10 disease

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

HSD10 disease is a disorder that affects the nervous system, vision, and heart. It is typically more severe in males than in females. Most affected males have a form of HSD10 disease in which early development seems normal, followed by a stage in which affected individuals rapidly lose skills they have acquired. This developmental regression often occurs between the ages of 1 and 2 and results in severe intellectual disability and loss of communication skills and motor skills such as sitting, standing, and walking. This form of the disorder is referred to as the infantile type. Less commonly, affected males have severe neurological problems from birth and never develop motor skills. This form is called the neonatal type. Males with the infantile or neonatal type frequently have weak muscle tone (hypotonia), recurrent seizures (epilepsy), and vision loss that gradually gets worse. Weakening of the heart muscle (cardiomyopathy) also occurs and is a common cause of death in males with severe HSD10 disease. Many affected males do not survive beyond early childhood.

Females with HSD10 disease may have developmental delay, learning problems, or intellectual disability, but they do not experience developmental regression. Some affected females have additional features of this condition, such as epilepsy, movement problems, and hearing loss. Affected females appear to have a normal life expectancy.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

HSD10 disease is caused by mutations in the HSD17B10 gene, which provides instructions for making the HSD10 protein. This protein is located within mitochondria, the energy-producing centers inside cells, where it is involved in the production (synthesis) of proteins. While most protein synthesis occurs in the fluid surrounding the nucleus (cytoplasm), a few proteins are synthesized in the mitochondria.

During protein synthesis, in either the mitochondria or the cytoplasm, molecules called transfer RNAs (tRNAs) help assemble protein building blocks (amino acids) into chains that form proteins. The HSD10 protein is part of a group of proteins (a complex) that is involved in making functional mitochondrial tRNA molecules, which aid in the synthesis of mitochondrial proteins. Normal mitochondrial protein production is essential for the formation of the groups of proteins that convert the energy from food into a form cells can use.

The HSD17B10 gene mutations that cause HSD10 disease reduce the amount of HSD10 protein in cells, impair their structure or function, or both, which leads to a deficiency of the functional complex in which it plays a part. This deficiency impairs the production of mitochondrial tRNAs. Without enough tRNAs, the mitochondrial synthesis of proteins involved in cellular energy production is reduced. A shortage of these proteins results in insufficient energy production in cells of the brain, eyes, and heart, leading to the characteristic features of HSD10 disease.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an X-linked pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes in each cell. In males, who have only one X chromosome, a mutation in the only copy of the gene in each cell is sufficient to cause the condition. In females, who have two copies of the X chromosome, one altered copy of the gene in each cell can lead to less severe features of the condition or may cause no signs or symptoms at all. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

HSD10 disease is a very rare disorder. Its prevalence is less than 1 in 1 million people.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal urinary acylglycine profile · Very frequent (99-80%)

An abnormal distribution of N-acylglycines in the urine. There are numerous different N-acylglycines, and this term refers to pathological alterations in their level or distribution.

Delayed speech and language development · Frequent (79-30%)

A degree of language development that is significantly below the norm for a child of a specified age.

Developmental regression · Frequent (79-30%)

Loss of developmental skills, as manifested by loss of developmental milestones.

Elevated urinary 3-hydroxybutyric acid · Frequent (79-30%)

An increased amount of 3-hydroxybutyric acid in the urine.

Global developmental delay · Frequent (79-30%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Intellectual disability, moderate · Frequent (79-30%)

Moderate intellectual disability (ID) is defined as a type of ID characterized by moderately sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 35-49.

Progressive visual loss · Frequent (79-30%)

A reduction of previously attained ability to see.

Seizure · Frequent (79-30%)

A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.

Other findings in the same source

From: Orphanet

Additional reported features include Specific learning disability (Frequent (79-30%)); Abnormal social behavior (Occasional (29-5%)); Ataxia (Occasional (29-5%)); Atypical behavior (Occasional (29-5%)); Autistic behavior (Occasional (29-5%)); Choreoathetosis (Occasional (29-5%)); Chronic lactic acidosis (Occasional (29-5%)); Dysarthria (Occasional (29-5%)); Floppy infant (Occasional (29-5%)); Frontotemporal cerebral atrophy (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing HSD10 disease is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for HSD10 disease. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.