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Infant Toddler Development Training
Module 1, Lesson 4

Causes of Prevalent Developmental Disabilities and Disorders (continued)


Degenerative Diseases

Muscular dystrophy is a disease that is genetically based and characterized by progressive muscle and skeletal weakness and degeneration (Sher, 1990). Some forms of muscular dystrophy are sex-linked (defective gene carried by mothers and passed on to sons) or autosomal-dominantly linked (defective gene carried by mother or father transmitted to son or daughter) or autosomal-recessively linked (defective gene carried by both the mother and father and transmitted to son or daughter) (Heller, Alberto, Forney, & Schwartzman, 1996). The most common as well as most severe of the muscular dystrophies is Duchenne Muscular Dystrophy (DMD) which manifests prior to age 6. Incidence of DMD is about 1 per 5,000 male live births.

Orthopedic and Musculosketal Disorders

Scoliosis is a sideways curvature of the spine. Scoliosis can either be nonstructural or structural curvatures. Nonstructural curvatures are generally due to secondary causes that are not permanent such as children who have legs that are different lengths or who have a herniated disk, both of which when corrected will correct the curvature of the spine. Structural curvatures of the spine are permanent. Causes range from unknown to genetic. Congenital causes are present at birth and tend to result in vertebrae that are malformed. Other causes of scoliosis result from central nervous system and muscular diseases such as cerebral palsy and muscular dystrophy. Additional causes may include trauma, malnutrition, bone diseases, and tumors.

Juvenile rheumatoid arthritis is joint inflammation that is chronic in which onset is prior to age 16. Specific causes of juvenile rheumatoid arthritis are unknown, however several causes have been proposed. One thought is that the body's antibodies attack normal cells and cause an autoimmune response. Another hypothesis is the presence of a microorganism infection causing inflammation in the joints. It is also thought that individuals with juvenile rheumatoid arthritis are genetically predisposed to the disease (Scholz & Albert, 1993)

Sensory Impairments

Children experience the world primarily through their vision and hearing. Deficits in either or both of these senses result in a barrier to effectively experiencing the world. When these barriers are addressed through early intervention appropriately (e.g., amplification, sign language, guided experiences, lenses) it is possible for the child with a hearing or vision impairment who has no other disability to develop at a rate similar to typically developing peers.

Visual Impairments Causes
Keratoconus diseases and disorders of the cornea  
Glaucoma abnormal increase in intraocular pressure
Color blindness chromosomal abnormalities
Strabismus eye muscle movement impairment results in incorrect eye alignment
Nearsightedness lens/cornea curvature deficits
Cataracts congenital infections or syndromes
Detached retinas trauma
Cortical blindness closed head injuries, drowning, or meningitis all resulting in brain damage
(Heller, Alberto, Forney, & Schwartzman, 1996)

Hearing impairment is any loss of hearing that affects a child's ability to access communication in their environment. Even mild and unilateral hearing loss will decrease a child's access to incidental language and communication opportunities. Severity of hearing loss is reported in decibel (dB) levels that refer to the loudness of a sound required for an individual to detect sounds of different frequencies (pitches). Mild hearing loss refers to a person who must have sound at least 26-40 dB loud before he or she can perceive that sound is present. A moderate degree of hearing loss occurs in a range of 41-55 dB, moderate-severe is 56-70 dB, severe is 71-90 dB, and profoundly deaf is defined as an inability to perceive sound, even when it is louder than 90 dB across the pitch range.

Hearing impairment is caused when physiological structures are damaged, deformed, or blocked. An ear canal plugged with ear wax or fluid or infection behind the eardrum will prevent a barrier to sound as it is conducted from the outer ear, to the inner ear. Thus, problems in the outer or middle ear cause conductive hearing losses. The cochlea within the inner ear is considered to be the sensory organ of hearing. When the hair cells that activate to the presence of sound in the inner ear are missing, damaged or deformed, the electrical signal that represents the sound cannot be transferred to the brain. Hearing loss due to problems with the hair cells in the inner ear is called a sensorineural hearing loss. Individuals can have problems in the hair cells of the cochlea and also have ear infections. Therefore, both sensorineural hearing loss and conductive hearing loss are present. In this situation the person will be said to have a mixed hearing loss. Hearing loss can also be progressive, requiring children with identified sensorineural hearing loss to have their hearing ability monitored every 3-6 months until school age. Finally, if the electrical signals generated in the cochlea to represent sound are not able to be processed, or cannot be processed effectively in the auditory cortex of the brain this is considered to be a central hearing loss, and more recently is called auditory dyssynchrony.

The incidence of permanent hearing loss in infants is 3/1000. Ear infections causing fluctuating conductive hearing loss are very common in infants and toddlers resulting in approximately 90% of children under the age of 3 having had at least one episode of ear infection, or otitis media.

Hearing Impairment Causes
Disorders of the outer ear (Conductive loss) Absence or closure of external ear canal Genetic inner ear abnormality Impacted ear canal (ear wax) Tumors Foreign bodies Swimmer's ear (infection of the skin of the external ear canal)
Disorders of the middle ear (Conductive loss) Bacterial/viral infection Obstructed Eustachian tube Middle ear infection (otitis media) Head trauma
Disorders of the inner ear and auditory nerve (Sensorineural loss) Congenital infections (Usher's syndrome) Trauma Loud noises Meningitis Damage to cochlea or auditory nerve
Disorders of the outer, middle, and inner ear (Mixed hearing loss) (All of the above causes can be considered for a mixed hearing loss)
Disorders of the central auditory system (Central hearing loss) Auditory dyssynchrony Brain tumors Acquired brain damage Vascular changes in the brain
Adapted from: (Heller, Alberto, Forney, & Schwartzman, 1996)


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