Can parents pass Balance Problems to their Children?
New developments in the field of genetics, and advanced techniques in assessing the human genome have lead to a deeper understanding of the genetic basis of the inheritance of balance disorders. Can balance problems be inherited? Yes, we now know that certain balance disorders can be inherited.
Inheritable conditions affecting the vestibular system:
Balance disorders were previously observed to cluster in families. They have now mapped the genes affected in many inheritable conditions that affect balance- mainly involving the Vestibular system and the cerebellum. Some of these are previously known conditions affecting balance. The newfound genetic evidence has lead to a better understanding of the pathophysiology of these diseases.
Conditions known to affect balance can be divided into those with normal hearing and those with impaired hearing. Research and study is ongoing. Discussing these conditions brings with it many unavoidable medical terms. We will do our best here to not overwhelm you.
Conditions with balance problems with normal hearing:
- Familial vestibular migraine
- Vestibular hypofunction
- Usher syndrome
- Menier’s disease
- Autosomal dominant nonsyndromic hearing loss ( DFNA -9,11,15)
- Enlarged vestibular aqueduct syndrome.
Conditions with balance problems with normal hearing:
Familial vestibular migraine:
Vestibular migraine is the most common cause of spontaneous (it just happens) recurrent vertigo (dizziness, spinning, perhaps with nausea).
It presents as recurrent episodes of vestibular symptoms with a current or previous history of migraine such as:
- spontaneous or positional vertigo
- visually induced vertigo (looking at movies, complicated patterns like railway station signage, driving)
- head motion-induced vertigo
- head motion-induced dizziness with nausea
- [International Classification of Headache Disorders (ICHD)]
Chromosomes usually involved in Familial vestibular migraine are chromosome 5q35, 11q and chromosome 22q12. The advanced technique known as Genome-wide analyses was instrumental in finding the linkage with these chromosomes.
Symptoms of vestibular migraine and Meniere disease overlap in some families. Also, both conditions can be inherited as a symptom cluster (2 or more symptoms that occur together).
Bilateral vestibulopathy that is, hypofunction (not working properly) of the vestibule of both sides without hearing loss has been described in some families. It usually presents without a migraine.
Vestibular hypofunction is linked to defects in chromosome 6q.
It presents with episodes of vertigo that are triggered by exercise and stress. They will also have an imbalance and head movement-dependent oscillopsia (feeling that your environment is constantly moving when it is actually stationary) developing at a later stage.
Conditions with balance problems with impaired hearing :
Usher syndrome affects vision and hearing. Since it involves inner ear even balance is affected.
Children with usher syndrome have delayed attaining milestones such as sitting independently, walking, riding a bicycle. This delay is because of problems with balance.
Meniere’s disease is a complex disease characterized by episodic vertigo, Sensory neural hearing loss, and tinnitus (ringing in ears).
Meniere’s disease is observed to run in some families. It follows the Autosomal dominant pattern of inheritance in these families.
Autosomal dominant nonsyndromic hearing loss ( DFNA -9,11,15):
The autosomal dominant pattern of inheritance means to say that disease will manifest even if one of the two copies of genes are affected ( one gene will be normal, one will be abnormal. The abnormal one will dominate).
DFNA 9 – mutations in the COCH gene.
Characterized by high-frequency Sensory Neural Hearing Loss and vertigo. It involves mutations in the COOH gene.
DFNA 11- mutations in the MYO7A gene.
Characterized by low and middle-frequency hearing loss (high pitched sounds can still be heard) and vestibular dysfunction. It involves mutations in the MYO7A gene.
DFNA 15: mutations in the POU4F3 gene
Presents as an early-onset progressive high-frequency hearing loss but also vestibular hypofunction. It involves mutations on the POU4F3 gene.
Enlargement of the vestibular aqueduct :
Enlargement of the vestibular aqueduct is the most common inner ear malformation seen ( a bit of anatomy that doesn’t form quite right)
Dilated vestibular aqueduct causing hearing and vestibular symptoms leads to Enlarged vestibular aqueduct syndrome.
Enlarged vestibular aqueduct syndrome has been associated with mutations on the SLC26A4 gene. This gene encodes protein pendrin.
Pendrin is a protein- it functions as anion exchanger in
- epithelial cells of the cochlea
- vestibular labyrinth
- endolymphatic sac
- thyroid gland ( so there.may be other problems beyond the vestibular system)
Other mutations seen in Enlarged vestibular aqueduct syndrome are FOXI1 gene mutations and KCNJ10 gene mutations.
Inheritable conditions affecting the cerebellum:
- Familial episodic ataxias
- Spinocerebellar ataxias
- Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS)
Ataxia is known to run in families. These ataxias have different forms of inheritance such as autosomal dominant, autosomal recessive, X-linked and mitochondrial inheritance.
Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS) is characterized by
- cerebellar ataxia (affects co-ordination and muscle strength)
- sensory neuropathy (numbness and weakness)
- bilateral vestibular loss (balance and visual)
- cerebellar atrophy involving anterior and dorsal vermis of the cerebellum (may affect the way we can stand)
The newer genetic techniques have opened a pandora box. This explains the basis of many balance disorders previously unknown. The medical world of balance disorders that can be inherited are overwhelming on first reading, however scientists are now exploring the possibility of newer gene therapy in these disorders. As gene therapy advances the query Can balance problems be inherited?, is soon going to be obsolete.