Down Syndrome

Down Syndrome

Definition:

Down syndrome, also called “trisomy 21”, is the most common chromosomal abnormality. It was first identified in 1866 by Dr. Langdon Down, who described the syndrome as “Mongolism”.

Incidence:

It occurs in 1: 800 live-births. It is equal between both sexes. It was not until 1959 that Lejeune identified the presence of extra chromosome in the G group, as responsible for the syndrome.

Types:

* 92%-95 % of cases are true trisomy, due to the non-disjunction in chromosome 21 during meiosis in the formation of gametes.

* 4 % of cases are translocation, where chromosome 21 is translocated to one of the chromosomes 14 or occasionally 22. This type can be hereditary and is not affected by parental age.

* 1 % of cases are mosaic type, where different cells of the body exhibit either normal or abnormal chromosomes. In this type, the children’s physical and cognitive impairment is related to the percentage of cells that exhibit abnormal chromosomes.

Etiology:

The exact cause of the additional chromosome is unknown. The incidence of Down syndrome increases markedly as maternal age increases. Paternal age can also be a factor.

Clinical features:

They are similar in all types of Down syndrome. The common features characterizing infants with Down syndrome include:

* Low birth weight.

* Low muscle tone (hypotonia).

* Joint laxity.

* Skull: Small circumference at 20th percentile.

* Bradycephaly: Short antero-posterior diameter of the head.

* Flat facial profile.

* Hair: Silky.

* Eye:

- Upward slanting.

- Brushiefed spots.

- Epicanthal folds.

* Flat nasal bridge.

* Protruded and fissured tongue.

* Ear:

- Small external ear.

- Over folded helix.

- Underdeveloped lobule.

* Neck: In infants, mottled skin (excess skin on the back of the neck).

* Hands:

- Short and broad hands.

- Clinodactyly (incurving of the 5th finger).

-Simian crease (joined two palmar transverse creases into one transverse crease).

* Mental retardation:Moderate to severe low intelligence quotient (IQ) from 25 % to 50 %. Mosaic type usually has higher IQ. About 35 % of Down syndrome patients have congenital heart disease.

* Persistence of primitive reflexes:

This includes the palmar reflex, planter grasping reflexes, the stepping reflex and the Moro reflex. Moreover, a delay in normal postural reactions is indicated by the evidence of severe head lag during elicitation of traction response.

* Other clinical features include small stature, convergent strabismus and nystagmus. In addition, cranio-facial differences such as shortened palate, small oral cavity due to hypo-plastic mandible, together with oral hypotonic tongue thrusting and poor lip closure,frequently result in feeding difficulties at birth.

* Orthopedic problems:

They include atlantoaxial instability. If this problem is not detected, there is increased risk of trauma, usually from hyper-flexion injuries. Consequently, there will be lower limb weakness and decreased walking abilities. Although hip dislocation is rare, it has been reported in cases of quadriplegia.

* Hearing impairment:

It is common as a result of structural defect and frequent ear infection.

Neuropathology:

1) Reduction of the brain weight in individuals with Down syndrome, as compared with normal individuals.

2) Reduction in size of the cerebral hemispheres, which is apparent in the frontal lobe poles, which explain the persistence of palmar grasp reflex in infants with Down syndrome, since a lesion in the frontal lobe of an adult may result in appearance of this reflex.

3) The brains of Down syndrome infants show smaller convolutions than those of normal infants of comparable age, indicating their relative neurologic immaturity.

4) Lower weight of the cerebellum and brain stem of this population may account for the muscular hypotonia, which in turn has a major influence on early motor development.

5) Cytologic abnormalities, including structural abnormalities in the dendritic spines of the pyramidal neurons of the motor cortex, resulting in incoordination and mental retardation.

6) Lack of myelination of the nerve fibers in the pre-central areas and frontal lobes of the cerebral cortex and in the cerebellum of infants with Down syndrome, which indicates lack of CNS maturity.

Common motor problems:

a)Muscle tone:Hypotonia, floppy child (rag doll).

b)Distribution:

It is generalized and symmetrical. Due to decreased muscle tone, children with Down syndrome tend to lock the weight bearing joints (e.g. knee joint) or assume posture that provides a broad base of support to maximize their stability.

c)Range of motion: Joint hyper-extensibility due to low muscle tone.

d)Deep tendon reflexes: Hypoactive.

e)Contractures and deformities:

There is a risk of dislocation of the atlanto-axial joint because of laxity of the transverse odontoid ligament. Dislocation of the hip joint may also occur. Spinal deformities are also present (lumber lordosis, thoraco-lumber scoliosis). Furthermore, two major foot deformities were noted. Those deformities are *metatarsus primus because of the gap found between the first and the second toe and *pes planus.

The main causes for contractures are generalized hypotonia, ligamentous laxity and gravitational force with bad positioning. For example, children with Down syndrome who adopt a constant position of wide abduction, external rotation and flexion at the hips (frog or reverse W-position) can develop soft tissue contractures in the hips or knees.

f)Integration of primitive reflexes:

Generally, there is hyporeflexia. Sometimes, delayed integration occurs. Those patients are characterized by delays in development of postural reactions. As a result, they often tend to relay on sources of external support to maintain upright positions.

g)Achievement of motor milestones:

There are delayed milestones, which correlate with the severity of hypotonicity. In addition to delayed integration of primitive reflexes, there is delayed development of automatic reactions. Those patients are also characterized by delays in the development of postural reactions. As a result, they often tend to rely on sources of external support to maintain the upright position. Children with Down syndrome, due to decreased muscle tone, tend to lock weight bearing joints (e.g. knee joint) or assume position that provide a broad base of support to maximize their stability.

h)Speech:

Delayed speech development is due to hypotonia of speech musculature.

Physical management

Assessment:

Evaluation of such cases should be comprehensive because of the multiplicity of the medical, cognitive and motor problems. Thus, prior to performing an evaluation, current medical information must be obtained about:

- The child’s cardiac status.

- Risk for atlanto-axial dislocation.

- History of seizures.

- Result of visual and auditory examination.

- The IQ and any behavioral problems.

Physical evaluation includes:

a)Qualitative evaluation:

It should include analysis of the manner, in which the infant with Down syndrome performs the movement (e.g. the ability to rise to sitting position independently from prone or supine positions). The child with Down syndrome characteristically spreads his legs until being in full split, with legs 180° from each other. Then, using his hands or head, he pushes up into the sitting position, with the legs still partially to fully in the split position.

b)Movement assessment of infants (MAT):

* Muscle tone (postural tone).

* Integration of primitive reflexes (hypo-reflexia or delayed integration).

* Righting, equilibrium and protective reactions.

* Volitional movements (Joint laxity, motor control).

* For children with orthopedic involvement, evaluation includes:

- Postural screening to detect postural deviation (fixed or mobile).

- Assessment of muscle strength.

- Range of motion assessment.

- Muscle flexibility.

c) Developmental and functional evaluation:

- To discriminate between typical and delayed development.

- To identify the constraints interfering with the achievement of functional skills.

- To guide the development of treatment goals and strategies.

Factors affecting normal pattern of movement:

- Lack of co-contraction.

- Generalized hypotonia (trunk and extremities).

- Hyper-extensibility of joints (hip joint).

- Lack of righting reactions (lack of trunk rotation).

- Lack of integration of primitive reflexes.

d)Self-care assessment:

Through self-care assessment,possible factors, which may interfere with the achievement of age-appropriate skills, can be determined. This may be due to:

* Neuro-motor deficits.

* Inappropriate behavior: For example, difficulty in drinking from a cup may be attributed to either:

- Generalized hypotonia, affecting the oral muscles, which leads to inadequate lip closure (neuromotor deficit).

- Throwing or dropping the cup (inappropriate behavior).

Appropriate treatment strategies:

a)Generalized hypotonia: Increase tone of the oral muscles through:

- Chin tapping.

- Volitional exercises in front of a mirror.

- Biofeedback.

b)Inadequate behavior: Behavioral programs of modeling appropriate cup drinking with an empty cup.

General treatment principles:

1. Focus on functional skills:

It depends on “task oriented approach”, in which the control of movement is organized around goal-directed functional behavior rather than muscle or movement patterns. Interventiontherefore is aiming at:

- Teaching motor problem solving.

- Developing effective compensations.

- Providing practice of new motor skills in functional situations.

1. Delivery of services in natural environment:

Functional skills must be taught and practiced within the context, where they will be used. For example:

- At home, provide therapeutic services in the home environment with consideration of the child’s needs within the context of the entire family.

- At school, the physical therapist should work with the teacher to provide therapeutic activities throughout the day in a natural manner. Music is a helpful tool and rhythm is a modality for developing skills.

1. Incorporating therapy activities into daily routines:

Therapy activities should be introduced in a natural manner, to be more meaningful to the child and his family. For example:

- Standing on one foot to pull on pants rather than practiced in isolation.

- Rather than asking the child to run from one end of the room to the other, use a game that requires running to play.

1. Use of assistive technology devices:

This is utilizes to help the child with Down syndrome to:

- Maximize his functional abilities.

- Increase the level of independence.

- Be enclosed in school.

- Achieve community activities with peers.

For example, adaptive devices such as prone standers and other positioning equipment maintain optimal body alignment, decrease risk for development of contractures and encourage a greater variety of movement patterns.

Physical therapy goals:

1)Improve head and trunk control.

2)Focus on developing motor skills that follow normal developmental patterns and sequences (e.g. rolling, creeping and rotation from sitting.

3)Modification of activities to avoid undue stress of the hyper-extensible joints and the surrounding structures, for example:

-Hyper-extensible ligaments cause excessive pronation in stance, which can be overcome by the use of ankle-foot orthoses to provide support and allow functional activities in standing.

-Standing with hyper-extended knee is controlled through the utilization of vertical standers to allow the child to stand and play with his knees in a more natural position.

4)Learning to walk: Children with Down syndrome almost learn to walk by an average of two years of age.

a)By this age period, focus should be directed on mobility skills, including pre-walking skills such as:

-Pulling to kneel-standing and standing.

-Moving in and out of a half kneeling position.

-Standing with and without support.

-Squatting from standing to pick up toys from the floor.

b) Advanced gait skills include:

-Walking up and down stairs.

-Walking on uneven terrain.

-Jumping, running and kicking a ball.

5)Reeducation of quality of movement: Integrated skills need:

a. Motor planning: The child should be taught how to coordinate arms, legs and trunk movements to obtain a motor goal, which may need verbal assistance or music (How to get sitting with rotation of trunk).

b. Coordination of graded movements: The child is learnt to do movement patterns smoothly, rather than in a jerky movement.

6) Development of co-contraction of proximal muscle groups:

This can be achieved by encouraging weight bearing through legs and arms, weight shifts in standing and sitting. For example, standing, standing on one leg, cruising, walking with hands, jumping, running, putting feet on footprints or dots. As those children suffer from instability, increasing of stability should be put into consideration.

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