Michel aplasia

Michel aplasia
Synonyms	Complete labyrinthine aplasia, CLA
Pronounce
Field	Otorhinolaryngology, Medical genetics
Symptoms	Profound congenital sensorineural deafness, balance impairment, microtia, microdontia
Complications	Delayed development, risk of trauma and accidents
Onset	At birth, or detectable within early childhood
Duration	Lifelong
Types
Causes	Mutations in the FGF3 gene, developmental failure of otic placode
Risks	Autosomal recessive inheritance in families with LAMM syndrome
Diagnosis	Clinical findings, CT scan or MRI, genetic testing for FGF3 mutation
Differential diagnosis	Other forms of congenital deafness, labyrinthitis ossificans
Prevention	Early intervention and precautions to prevent accidents
Treatment	Early intervention for deafness, vibrotactile hearing devices, cochlear implantation (if applicable)
Medication
Prognosis	Dependent on early intervention, limited hearing ability
Frequency	Rare
Deaths	No direct cause of death, but risk due to associated developmental delays

Alternate names

• Complete labyrinthine aplasia (CLA)

Definition

Michel aplasia is a rare congenital abnormality of the inner ear that results in the complete absence of inner ear structures, leading to profound sensorineural deafness (congenital anacusis). It is also referred to as complete labyrinthine aplasia (CLA) and is associated with other abnormalities, including microtia (underdeveloped outer ear) and microdontia (small teeth).

Pathology

Michel aplasia occurs due to failure in the development of the otic placode, a structure involved in the formation of the inner ear. This developmental failure typically happens during the first few weeks of gestation. In the third week, there is a developmental arrest that leads to a common cavity deformity, which is characterized by a confluence of poorly defined cochlea and vestibular organs. If this arrest happens later in gestation, particularly during the fourth to sixth week, it can result in either cochlear aplasia or cochlear hypoplasia.

Associations

Michel aplasia is associated with LAMM syndrome, a condition caused by a mutation in the FGF3 gene (fibroblast growth factor 3), located on chromosome 11q13. LAMM syndrome is characterized by:

• Labyrinthine aplasia (absence of the inner ear structures)
• Microtia (underdeveloped external ear)
• Microdontia (small-sized teeth)

The inheritance of Michel aplasia is autosomal recessive, which means that affected individuals inherit two copies of the mutated gene, one from each parent.

Diagnosis

Diagnosis of Michel aplasia is based on a combination of clinical findings, imaging studies, and genetic testing:

• Clinical findings: Profound congenital sensorineural deafness is the hallmark of the disorder.
• Imaging: CT scans or MRI of the inner ear reveal the absence of recognizable structures, such as the cochlea and vestibule.
• Molecular genetic testing: Genetic testing to detect mutations in the FGF3 gene can confirm the diagnosis. Testing for mutations in the FGF3 gene is especially helpful in families with a history of LAMM syndrome.

Treatment

Treatment of Michel aplasia primarily focuses on managing the profound deafness and promoting early development. Treatment options include:

• Early intervention programs: Enrollment in programs for the deaf and hard of hearing is crucial for language development and communication skills.
• Vibrotactile hearing devices: These devices use vibrations to convey sound to the user and can be helpful for those who cannot benefit from traditional hearing aids.
• Cochlear implants: For individuals with a cochleovestibular nerve and a cochlear remnant, cochlear implants may be considered. This option is typically available for children over 12 months old, although the approach is contested by the Deaf community and may come with complications.
• Multidisciplinary surveillance: Annual evaluations by a team of specialists, including an otolaryngologist, clinical geneticist, pediatrician, and neurologist, help monitor the individual's progress and development.

Prevention (of secondary complications)

Preventing secondary complications focuses on minimizing the risks associated with hearing loss and developmental delays:

• Safety measures: Given the balance impairment and profound deafness, individuals with Michel aplasia are at increased risk for trauma and accidents. Installing visual or vibrotactile alarm systems in homes and schools, as well as providing anticipatory education for parents and caregivers, can help reduce these risks.
• Developmental support: Early intervention programs to support cognitive, speech, and physical development are important to mitigate developmental delays.

Prognosis

The prognosis of individuals with Michel aplasia largely depends on the availability of early intervention and the severity of associated symptoms. Although the hearing loss is profound, individuals with appropriate interventions can lead productive lives. However, developmental delays, especially those related to balance and communication, can persist.

Epidemiology

Michel aplasia is an extremely rare disease, with limited documented cases. It was first described by P. Michel in 1863, following the autopsy of an 11-year-old child who exhibited deafness and an absence of inner ear structures.

See Also

• Labyrinthine aplasia
• Microtia
• Microdontia
• Congenital hearing loss
• Autosomal recessive inheritance
• Sensorineural deafness

External links

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