Brain-lung-thyroid syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Brain-lung-thyroid syndrome is a group of conditions that affect the brain, lungs, and thyroid gland (a butterfly-shaped gland in the lower neck). Brain-lung-thyroid syndrome historically included problems with all three organs, although the designation now encompasses a combination of brain, lung, and thyroid problems. About 50 percent of affected individuals have problems with all three organs, about 30 percent have brain and thyroid problems, and about 10 percent have brain and lung problems. The brain alone is affected in 10 to 20 percent of people with the condition. Such cases are sometimes called isolated benign hereditary chorea.

Nearly everyone with brain-lung-thyroid syndrome has brain-related movement abnormalities. Benign hereditary chorea is the most common feature of the syndrome. This feature is associated with involuntary jerking movements (chorea) of the face, torso, and limbs; writhing movements (athetosis) of the limbs; and other movement problems. Individuals with brain-lung-thyroid syndrome can have other abnormalities, such as difficulty coordinating movements (ataxia), muscle twitches (myoclonus), and involuntary muscle contractions that result in twisting and repetitive movements (dystonia). The movement problems typically begin around age 1, although they can begin in early infancy or later in life, and are often preceded by weak muscle tone (hypotonia). They can delay the development of walking. The movement problems usually remain stable and can improve over time. Some affected individuals also have learning difficulties or intellectual disability.

Thyroid problems are the next most common feature of brain-lung-thyroid syndrome. The thyroid gland makes hormones that help regulate a wide variety of critical body functions, including growth, brain development, and the rate of chemical reactions in the body (metabolism). Many affected individuals have reduced thyroid function from birth (congenital hypothyroidism), resulting in lower-than-normal levels of thyroid hormones. Others have a milder condition called compensated or subclinical hypothyroidism, in which thyroid hormone levels are within the normal range, even though the thyroid is not functioning properly. While most people with brain-lung-thyroid syndrome have a normal-sized thyroid, the gland is reduced in size (hypoplastic) or absent (aplastic) in some affected individuals. Although a shortage of thyroid hormones can cause intellectual disability and other neurological problems, it is unclear whether such issues in individuals with brain-lung-thyroid syndrome are due to hypothyroidism or to the brain abnormalities related to the condition.

Lung problems are common in brain-lung-thyroid syndrome. Some affected newborns have respiratory distress syndrome, which causes extreme difficulty breathing and can be life-threatening. Other affected individuals develop widespread lung damage (interstitial lung disease) or scarring in the lungs (pulmonary fibrosis), both of which can also lead to breathing problems. Recurrent lung infections, which can be life-threatening, also occur in people with brain-lung-thyroid syndrome. People with brain-lung-thyroid syndrome have a higher risk of developing lung cancer than do people in the general population.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Brain-lung-thyroid syndrome is caused by genetic changes that affect the NKX2-1 gene, which provides instructions for making a protein called homeobox protein Nkx-2.1. This protein functions as a transcription factor, which means it attaches to DNA and controls the activity (expression) of other genes. By regulating the expression of certain genes during embryonic development, homeobox protein Nkx-2.1 helps direct the development of the brain, lungs, and thyroid gland and promotes their normal function. Mutations in or deletion of the NKX2-1 gene lead to a reduction in the amount of homeobox protein Nkx-2.1 or impair its function. As a result, the expression of genes controlled by homeobox protein Nkx-2.1 is altered, which impedes the normal development and function of the brain, lungs, or thyroid gland. Problems with these organs underlie benign hereditary chorea, respiratory distress syndrome, congenital hypothyroidism, and other features of brain-lung-thyroid syndrome. It is unclear why all three organs are affected in some individuals with the condition, while only one or two are affected in others.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In some cases, an affected person inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Brain-lung-thyroid syndrome is a rare disorder; its prevalence is unknown.

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.

Abnormality of the thyroid gland · Very frequent (99-80%)

An abnormality of the thyroid gland.

Abnormality of the nervous system · Frequent (79-30%)

An abnormality of the nervous system.

Abnormality of the respiratory system · Frequent (79-30%)

An abnormality of the respiratory system, which include the airways, lungs, and the respiratory muscles.

Ataxia · Frequent (79-30%)

Ataxia refers to impaired coordination of voluntary muscle movement. Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).

Chorea · Frequent (79-30%)

Chorea (Greek for 'dance') refers to widespread arrhythmic involuntary movements of a forcible, jerky and restless fashion. It is a random-appearing sequence of one or more discrete involuntary movements or movement fragments. Movements appear random because of variability in timing, duration or location. Each movement may have a distinct start and end. However, movements may be strung together and thus may appear to flow randomly from one muscle group to another. Chorea can involve the trunk, neck, face, tongue, and extremities.

Choreoathetosis · Frequent (79-30%)

Involuntary movements characterized by both athetosis (inability to sustain muscles in a fixed position) and chorea (widespread jerky arrhythmic movements).

Congenital hypothyroidism · Frequent (79-30%)

A type of hypothyroidism with congenital onset.

Floppy infant · Frequent (79-30%)

Floppiness/hypotonia is defined as reduced resistance to passive movement of joints. Physical examination of floppy/hypotonic infants shows head lag, lack of shoulder and elbow muscle contraction on traction response, inability to tighten the shoulder girdle muscles (or slipping through) when held under the axillae, scarf sign (when the arm is pulled to the opposite side, the arm wraps around the neck with the elbow crossing midline), hyperdorsiflexion of the feet, easy apposition of the thumb against the forearm, feet touching the cheek with ease and without discomfort, frog leg position, and inverted U sign on ventral suspension (head, arms, and legs hanging down without elbow or knee flexion and the trunk rounded in a dome shape).

Other findings in the same source

From: Orphanet

Additional reported features include Neonatal respiratory distress (Frequent (79-30%)); Respiratory distress (Frequent (79-30%)); Abnormal cardiac septum morphology (Occasional (29-5%)); Abnormal pulmonary interstitial morphology (Occasional (29-5%)); Apraxia (Occasional (29-5%)); Atrial septal defect (Occasional (29-5%)); Clumsiness (Occasional (29-5%)); Compensated hypothyroidism (Occasional (29-5%)); Dysarthria (Occasional (29-5%)); Dystonia (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 Brain-lung-thyroid syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

Additional services that may be relevant, depending on the findings, include: Pulmonology.

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.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Brain-lung-thyroid syndrome. 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.