Introduction

Some children might not be as active and smart as their peers and many of them with genetic abnormalities are diagnosed at birth or at an early age. The most common among the genetic disorders which may result in children with typical low IQ is Down’s syndrome. There are three types of Down syndrome: trisomy 21 (nondisjunction), translocation and mosaicism. Down syndrome is the most frequent genetic cause of mild to moderate learning disability. It is found in 1 of every 800 live births.

• Trisomy 21 (nondisjunction)

  Trisomy or non-disjunction is the most common type of Down ’s syndrome. It is caused by the error in cell division which results in three copies of chromosome 21 instead of the usual two. It happens due the fact that sometimes a pair of 21 chromosome in either of the two- egg or sperm, prior to conception fails to separate and this results in faulty combination of three set of chromosome. So this results in trisomy 21 in all cells of body and hence causes Down’s syndrome.

• Mosaicism

  Mosaicism Is a kind of non-disjunction which results in the trisomy of 21 chromosomes in not all the cells, unlike the true trisomy and mosaicism the non-disjunction occurs after fertilization. This result in a mixture of two types of cells, some containing the usual 46 chromosomes and some contains 47. It is less common variant of Down’s syndrome. Since in this kind of Down’s syndrome all the cells are not affected; fewer symptoms are seen as compared to trisomy 21.

• Translocation

  Translocation is also a less common variant of Down syndrome. In translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome, typically chromosome 14. Unlike the other variants there is not an extra chromosome 21 but the chromosomal aberration resulting from breakage of chromosome 21 also results in the characteristic feature of Down’s syndrome. In this variant the total number of chromosome remains 46 but chromosomal aberration results in Down syndrome.

Causes

1. Advanced maternal age: Maternal is a very important deciding factor in the causation of Down syndrome. As the maternal age advances the probability of baby having Down syndrome increases with the maximum incidence when maternal age at time of conception is in forty’s.
2. Uterine and placental abnormalities
3. Chromosomal aberrations

General manifestations

The characteristic features of Down syndrome are:

1. Neuropsychiatric:
   1. Learning disability
   2. Dementia
   3. Memory loss and impaired judgment
   4. Alzheimer’s disease
   5. Severely retarded IQ – 25-50
2. Endocrine:
   1. People with Down syndrome are especially vulnerable to thyroid disease - Hypothyroidism
3. Sensory deficits:
   1. Hearing defects - the external ear and the bones of the middle and inner ear may develop differently, therefore up to 90% have hearing loss of greater than 15–20 decibels in at least one ear
   2. Visual defects - cataracts, nystagmus, strabismus
4. Cardiac problems:
   1. Early onset pulmonary hypertension
   2. Congenital heart disease - TYPES: atrial septal defect, mitral valve prolapse, atrioventricular canal and ventricular septal defect.
5. Spinal problems:
   1. Atlantoaxial instability - can cause spinal cord compression if the neck is not handled considerately
   2. Susceptibility to transient myelodysplasia, or defective development of the spinal cord
6. Malignancies:
   1. More likely than others to develop leukaemia
   2. Predisposition to retinoblastoma
7. Immune defects:
   1. There are multiple immunological defects (IgA and T lymphocyte function defects) so that infections of the skin, gastrointestinal and respiratory tracts are common, especially in institutionalised patients who are also liable to be hepatitis B carriers (persistence of HBsAg in about 40% of individuals).
8. Respiratory infections:
   1. Frequent upper respiratory infections
   2. Chronic respiratory infections may include recurrent middle ear, tonsil, nasal and sinus infections and tuberculosis.

Down syndrome affects many if not most organs. Following manifestations can be seen:

1. Skull:
   1. Round skull resulting in a flattened face and occiput
   2. Flat nasal bridges with a small maxilla
2. Eyes:
   1. Scanty eyelashes
   2. Oblique palpebral fissures with prominent epicanthic folds (Mongoloid Face in 85%)
   3. Brushfield’s spots appear on the iris in a ring concentric with pupil
3. Ears: Dysplastic ears with abnormal pinna
4. Neck: Short and broad with excess skin posteriorly
5. Hands:
   1. Broad and short with a single transverse palmar crease
   2. Short incurved little finger (clinodactyly)
   3. Multiple loops on finger tips
6. Muscle and joints: Hypotonicity and hyperflexibility
7. Abdomen and pelvis:
   1. Umbilical hernia
   2. Pelvic dysplasia (70%)
8. Body proportions and development:
   1. Short stature (85%)
   2. Premature ageing

Oral manifestations

1. Mouth:
   1. Small drooping mouth
   2. Open mouth posture
2. Tongue:
   1. Protrusive, fissured tongue
   2. Macroglossia
   3. Enlarged circumvallate papilla and absence of filiform papilla
3. Lips: Thick, dry and fissured
4. Occlusion:
   1. Anterior open bite and crossbite
   2. Small maxilla
5. Palate:
   1. High palate with horizontal palatal shelves
   2. Bifid uvula, cleft lip and palate
6. Teeth:
   1. Retarded eruption and early shedding of deciduous teeth
   2. Microdontia and Hypodontia
   3. Hypoplastic defects
7. Periodontium:
   1. High incidence of rapid and destructive periodontal diseases due to various local and systemic factors

Diagnosis

Prenatally (Before birth)

There are some tests that can be performed before child’s birth to ensure that the child won’t have any chromosomal or developmental abnormality. These tests can be either screening or diagnostic tests. However screening tests provide just the probability but diagnostic tests are accurate in providing the results.

The screening tests include sonography and the blood tests. The blood tests and the sonogram are performed in a very elaborate way to check for the markers in the susceptible mother.

Nowadays there are prenatal screening kits that are also available which are non-invasive and provide the definitive results. Some of the diagnostic procedures are chorionic villus sampling (CVS) and amniocentesis. However they are not safe as they are invasive and may even result in miscarriage.

At Birth

Down syndrome is usually identified at birth by the presence of certain physical symptoms like low muscle tone, a single deep crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes. But these are not definitive as these features may be present in babies without Down syndrome; a chromosomal analysis called a karyotype can also be performed to confirm the diagnosis. Another genetic test called FISH can apply similar principles and confirm a diagnosis in a shorter amount of time.

Treatment

1. Behaviour, intelligence and functional development - Children with Down syndrome (10%) are mentally retarded, may be aggressive or frustrated and require appropriate speech therapy, behavioural therapy, intelligence and functional development approaches as treatment.
2. Surgical and medical management of organ deficits - gastrointestinal blockage, heart defects and cataract require surgical intervention immediately after birth or at a later stage along with appropriate medications.
3. Breastfeeding - In infants, problems may be faced during breastfeeding. Due to poor tongue control, leakage of milk occurs while suckling. Proper head support should be given while breastfeeding and the child should be well awake.
4. Proper Diet - Older children are more susceptible to obesity due to high-calorie intake and therefore a healthy and balanced diet is must.
5. Precautions against drug abuse and pregnancy - Adolescents are susceptible to drug abuse and unplanned or early pregnancies. Therefore, should be explained and made aware about adequate precautions for pregnancy control. They should be given adequate freedom yet be kept in a safe environment.
6. Prophylaxis - Incidence of cardiac diseases associated with Down’s syndrome is 40% and therefore requires adequate prophylaxis against bacterial endocarditis before any surgery.
7. Surgical Anaesthesia and analgesia - Nitrous oxide analgesia used in mildly apprehensive patients and general anaesthesia in patients with severe resistance to surgical treatment.
8. Proper oral hygiene should be maintained to reduce the risk of dental problems
9. Dental Treatment - Pulp procedures as pulpectomy or root canal treatments are contraindicated in deciduous teeth in patients with cardiac defects because of the risk of bacteraemia whereas in permanent teeth it can be considered in severe cases. Extraction of the tooth is preferred over long and multiple sitting pulp procedures.

References

1. Current Pediatric Therapy, Eighteenth Edition. Fredric D. Burg, Julie R. Ingelfinger, Richard A. Polin, Anne A. Gershon. Elsevier Inc. ISBN-13: 978-0-7216-0549-4.
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3. Textbook of Pedodontics, Second Edition. Shobha Tandon, Paras Medical Publisher, ISBN 978-81-8191-241-1.
4. Dentistry for the Child and Adolescent, Ninth Edition. Jeffrey A. Dean, David R. Avery, Ralph E. McDonald. Elsevier Inc. ISBN 978-0-323-05724-0
5. Handbook of Pediatric Dentistry, Third Edition. Angus C. Cameron, Richard P. Widmer. Mosby Elsevier Limited, ISBN 978 0 7234 3452 8.
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7. Pediatric Secrets, Fourth Edition. Richard A. Polin, Mark F. Ditmar. Elsevier Mosby.
8. Babies with Down Syndrome: A New Parent's' Guide (Third Edition). Skallerup, S. (Ed.) Bethesda, MD: Woodbine House. (2008)