4/20 Ch 8 genetic disorders

Down syndrome

is a leading chromosomal cause of mental retardation and the most frequently reported birth defect. Risk factors include increasing maternal and paternal age Caused by genetic imbalance resulting in an extra 21st chromosome commonly referred to as trisomy 21

Arthrogryposis Multiplex Congenita (AMC)

1/3 of all cases are genetic: Neuropathic form involve chromosome 5 Distal AMC involves chromosome 9 Non-progressive neuromuscular syndrome. AMC results in multiple joint contractures and usually requires surgical intervention to correct misaligned joints. AMC is also known as multiple congenital contractures The incidence of the disorder is 1 in 3,000 live births

OI

All rotations should be active, not passive, performing a traditional pull-to-sit maneuver is contraindicated with these patients

Clubfoot

Ambulation is achieved by most children with AMC by 18 months of age this is often a part of the presentation in AMC, and generally involves early surgical correction

Osteogenesis imperfecta

Autosomal dominant disorder of collagen synthesis that affects bone metabolism. Individuals with OI have "brittle bones." Many also exhibit short stature, bowing of long bones, ligamentous joint laxity, and kyphoscoliosis. There are four types Depending on the type of OI, the infant may be born with multiple fractures or may not experience any broken bones until reaching preschool age. Average or above-average intelligence is typical.

Nondisjunction

Cells divide unequally

Postural Drainage tx CF

Central to the care of the child with CF is chest physical therapy (CPT). It consists of bronchial drainage in specific positions with percussion, rib shaking, vibration, and breathing exercises and retraining. Parents are taught to perform postural drainage three to five times a day. Adequate fluid intake is important to keep the mucus hydrated and therefore make it easier to move and be expectorated

Down Syndrome

Characteristic features of the child with DS include Hypotonicity Joint hypermobility Upwardly slanting epicanthal folds Flat nasal bridge and facial profile The child has a small oral cavity that sometimes causes the tongue to seem to protrude. Delayed development and impaired motor control. Feeding problems may be evident at birth and may require intervention. Approximately 40 to 66% of children with DS also have congenital heart disease which can usually be corrected by cardiac surgery. Musculoskeletal manifestations may include pes planus (flatfoot), thoracolumbar scoliosis, and patellar and possibly atlantoaxial instability. The incidence of atlantoaxial instability (AAI) ranges from 15 to 20%

Chronic Childhood SMA

Chronic type II SMA has a later onset, which is reported to occur between 2 and 18 months. This type is characterized by the onset of proximal weakness, similar to the infantile type, and has the same incidence in the population. It may be difficult for these children to develop the ability to sit without orthotic support. Because of trunk muscle weakness, scoliosis is a pervasive problem and may require surgical intervention. 12 to 15% fracture rate, weight bearing is also recommended as part of any therapeutic intervention to prevent fractures recommended a supine stander for children who lack adequate head control. Life expectancy is variable, with some reaching adulthood and others die in childhood. The course of the disease is rapid at first and then stabilizes; therefore, the range of disability can be varied. Physical therapy goals can also be directed toward attaining some type of functional mobility. Prognosis depends on the degree and frequency of pulmonary complications. Postural drainage positioning can be incorporated into the preschool, school, and home routine. Respiratory compromise remains the major cause of death

Phenylketonuria

Genetic cause of mental retardation that is preventable is phenylketonuria (PKU), an inborn error of metabolism. PKU is caused by an autosomal recessive trait that can be detected at birth by a blood test. The infant's metabolism is missing an enzyme that converts phenylalanine to tyrosine. Too much phenylalanine causes mental and growth retardation along with seizures and behavioral problems. Once the error is identified, infants are placed on a phenylalanine-restricted diet.

70-75

Must have IQ of to be diagnosed as having mental retardation.

Kugelberg-Welander SMA

Onset after 18 months. This is the least involved form, with an incidence of 6 in 100,000 live births with onset anywhere from 2 to 15 years. Characteristics include proximal weakness, which is greatest in the hips, knees, and trunk. Developmental progress is slow, with independent sitting achieved by 1 year and independent walking by 3 years. The gait is slow and waddling, often with bilateral Trendelenburg signs. These children have good upper extremity strength

Becker Muscular Dystrophy

Onset of symptoms between 5 and 10 years of age, live into their forties. This X-linked dystrophy occurs in 3 to 6 per 100,000 males, rarer than DMD. Dystrophin continues to be present but in lesser amounts than normal and lower incidence of mental retardation with the Becker type of dystrophy. Same physical therapy management as with DMD; but, the progression of the disorder is much slower. Greater potential and expectation exist for the individual to continue to ambulate until his late teens. Prevention of excessive weight gain must be vigorously pursued to avoid use of a wheelchair too early, because life expectancy reaches into the forties. Death secondary to pulmonary or cardiac failure

Translocation:

Part of one chromosome detaches and reattaches to a completely different chromosome

PRADER-WILLI SYNDROME

Partial deletion of chromosome 15 with an incidence of 1 in 10,000 to 1 in 20,000 live births. Diagnosed by behavior and clinical features, not genetic testing. Typical clinical features include: obesity, underdeveloped gonads, short stature, hypotonia, and mild to moderate mental retardation Become obsessed with food by age 2, , but before this age they have difficulty in feeding secondary to low muscle tone and they gain weight slowl

Spinal Muscular Atrophy

Progressive disease of the nervous system inherited as an autosomal recessive trait The anterior horn cell undergoes progressive degeneration. Children with SMA exhibit hypotonia of peripheral, rather than of central, origin. Damage to lower motor neurons produces low muscle tone or flaccidity, depending on whether some or all of the anterior horn cells degenerate. Muscle fibers have little or no innervation from the spinal nerve if the anterior horn cell is damaged, and the result is weakness. SMA occurs in 1 of 10,000 live births and is the second most common fatal recessive genetic disorder seen in children, after cystic fibrosis.

Acute Infantile SMA

The earliest-occurring, most physically devastating form is type 1, acute infantile SMA. The incidence is 1 in 15,000 to 1 in 25,000 births, onset between birth and 2 months. The child is limp, "frog-legged" lower extremity posture is evident at birth, along with a weak cry. Deep tendon reflexes are absent, and the tongue may fasciculate (quiver) because of weakness. Most infants are sociable and interact appropriately because they have normal intelligence. Motor weakness progresses rapidly, and death results from respiratory compromise. Infants with type I SMA usually die within 2 to 3 years of age.

Deletion:

When all or part of a chromosome is lost

Cri-du-chat Syndrome

When part of the short arm of chromosome 5 is deleted, the result is the cat-cry syndrome, or cri-du-chat syndrome. The chromosome abnormality primarily affects the nervous system and results in mental retardation. The incidence is 1 in 20,000 to 1 in 50,000 live births Primarily affects the nervous system and leads to mental retardation Clinical features include a cat like cry (usually only in infants), microcephaly, wide spaced eyes, and profound mental retardation

Fragile X syndrome

also known as Martin-Bell syndrome, is the leading inherited cause of mental retardation. It occurs in 1 per 2,000 males and 1 per 4,000 females The disorder is characterized by mental retardation, unusual facies, poor coordination, a generalized decrease in muscle tone, and enlarged testes in male patients after puberty. These children have a long, narrow face with a prominent forehead, jaw, and ears.

Genes

carry the blueprint for body systems

Rett syndrome

is a neurodevelopmental disorder that almost exclusively affects females. It occurs in approximately 1 in 12,000 females. The presentation in females suggests an X-linked dominant means of inheritance Rett syndrome is characterized by mental retardation, ataxia, and growth retardation. It is a major cause of mental retardation in females. Brain growth is reduced, and the brain's ability to form new synapses is severely impaired Early development in affected infants is normal, with symptoms usually appearing during the first year of life. The hypotonia present in infancy is replaced by increasing hypertonia and loss of acquired skills. These children develop stereotypical hand movements, such as flapping, wringing, and slapping, as well as mouthing. Decline in function during childhood includes a decreased ability to communicate, seizure activity, and, later, scoliosis.

Cystic fibrosis

is an autosomal recessive disorder of the exocrine glands that is caused by a defect on chromosome 7. CF produces respiratory compromise because abnormally thick mucus builds up in the lungs. This buildup creates a chronic obstructive lung disorder. The incidence is 1 in 2000 live births in whites. Diagnosis CF is the most lethal genetic disease in whites. Diagnosis can be made on the basis of a positive sweat chloride test. Children with CF excrete too much salt in their sweat, and this salt can be measured and compared with normal values. Some mothers have even stated that the child tastes salty when kissed.

The Gower maneuver (Gower Sign)

is characterized by the child using his arms to push on the thighs to achieve a standing position from the floor. This maneuver indicates muscle weakness. The diagnosis is usually made during this time

DMD

is transmitted as an X-linked recessive trait, only manifested only in boys. Females can be carriers of the gene, but they do not express it DMD affects 1 in 3,500 male births Two thirds of cases of DMD are inherited, whereas one third of cases result from a spontaneous mutation. Boys with DMD develop motor skills normally. However, between ages 3 and 5 years, they may begin to fall more often or to experience difficulty in going up and down stairs, or they may use a characteristic Gower maneuver to move into a standing position from the floor The Gower maneuver is characterized by the child using his arms to push on the thighs to achieve a standing position. This maneuver indicates muscle weakness. The diagnosis is usually made during this time.