Case• 6. Down’s syndrome
SUMMARY
A 40-year-old male patient presents to you in your dental surgery with a loose tooth. What is the cause and what will you do?
History
Complaint
The patient has been complaining of a sore, loose lower back tooth for 1 week. It is particularly sore when eating and the patient often flinches whilst chewing.
History of complaint
There were no recent symptoms from this tooth until 1 week ago. When the pain started, the patient’s mother noticed that he stopped bruxing.
Dental history
He has been seen in your practice for several years and attends with his mother on most occasions (Figure 6.1).
 |
| Fig. 6.1 |
You have been monitoring his periodontitis for many years. The patient achieves a moderate degree of oral hygiene but cleaning posteriorly is always suboptimal. He has had a series of episodes of acute symptoms from this tooth but has always refused to let you extract it.
Medical history
The patient has Down’s syndrome. He has a patent ventriculoseptal defect that is unrepaired and a mild to moderate learning disability. He reports recurrent upper respiratory tract infections.
Social history
The patient lives at home with his parents and works part-time in a supermarket. He does not smoke or drink any alcohol.
▪ What are the causes of Down’s syndrome?
Down’s syndrome is caused by complete or partial trisomy of chromosome 21. The majority of patients have a complete third copy of the chromosome, but there are several different ways in which cells can acquire additional chromosome 21 DNA. This is important because not all individuals with Down’s syndrome have a similar phenotype. The types of trisomy 21 are explained in Table 6.1.
| Type of trisomy | % of patients | Cause | Significance |
|---|---|---|---|
| Free trisomy Down’s syndrome | 95% | A ‘free’ third copy of chromosome 21 in every cell. Meiotic non-disjunction (failure of chromosomes or chromatids to separate during cell division) in development of the egg (95%) or sperm (5%) results in gametes with an extra copy of chromosome 21. After fertilization and embryogenesis, every cell carries a copy of the third chromosome | Commonest type. Not inherited |
| Translocation Down’s syndrome | 2% | One copy is translocated to another chromosome, most often chromosome 14 or 21, in a cell division during development of the egg, or occasionally sperm. Sometimes the translocation affects only the child. Occasionally the translocation is stable and can be passed from generation to generation | About half of cases have a familial pattern of inheritance |
| Mosaic Down’s syndrome | 2% | Patients are a mosaic of normal cells and cells with trisomy 21. The gametes are normal but non-disjunction during a somatic division in embryogenesis gives some cells trisomy. If the trisomy arises early a large proportion of the patient’s cells are affected; if late, fewer are affected | The features vary depending on which cells are affected. Some patients may be of Down’s appearance but normal intelligence or vice versa, and the features are often mild. Not inherited |
| Other types | 1% | Caused by a variety of different chromosomal rearrangements involving chromosome 21 |
▪ How does this cause the condition?
The long arm of chromosome 21 includes a region called the Down syndrome critical region. Genes at this site encode transcription factors that control development, including that of the brain. An increase in copy number of genes in this region is thought to account for most of the neurological and facial, and possibly other, features of Down’s syndrome. Other genes have been identified for leukaemia and other complications.
▪ What is the risk of having a child with Down’s syndrome?
Because most cases are caused by chromosomal non-disjunction during egg formation, the risk is linked to maternal age. The risk rises markedly after 40 years. The risk in a mother aged 30 is approximately 1 in 1000 but this rises to almost 1 in 100 at age 40 years and higher after that.
Prenatal screening relies on a variety of tests, including ultrasound screening. The most accurate tests require amniocentesis and are reserved for those at the highest risk. The newest tests promise accurate diagnosis on the basis of a blood test. The combination of prenatal testing and termination of pregnancy has resulted in falling incidence in many parts of the world. This is somewhat compensated for by a generalized increase in maternal age and greater life expectancy for those affected.
Two-thirds of affected fetuses die during normal development and the frequency of trisomy 21 in the population is 1 in 650–1000 live births.
A wide range of terms may be used to describe intellectual ability. Terms such as mental retardation, intellectual impairment and mental subnormality are no longer used in the UK, though they are considered acceptable in other cultures. Learning difficulty and learning disability are considered synonymous in the UK. Mental incapacity is a legal term used to describe ability to make informed decisions. It relates to intellectual ability but is not the same as learning difficulty.
Learning difficulty is defined as a significant impairment of intelligence and social functioning acquired before adulthood. The definitions are from the Education Act 1996 and the Special Educational Needs and Disability Act 2001 that define the educational needs and aid the individual in gaining access to legal protections and rights.
Learning difficulty is usually divided into mild, moderate and severe, but these definitions are not always helpful in health care because they are based on analysis of social functioning as well as psychometric testing. The categories do not correlate directly with intelligence, though they are often equated, as shown in Table 6.2.
| Learning difficulty/disability | Indicative IQ | Effects |
|---|---|---|
| Mild | 50–70 | Most can lead normal lives but may need assistance in handling difficult situations |
| Moderate | 35–49 | Need to use simple language when talking. Can generally attend to the basic tasks of life after training but more complex activities such as using money usually require support within a special residential environment |
| Severe | 20–34 | Many able to look after themselves but with careful and close supervision |
The majority of individuals with Down’s syndrome have mild to moderate learning difficulty. Regardless of learning difficulty, all those with Down’s syndrome will require lifelong help with accommodation and supportive working. Some can lead largely independent lives with support whereas, for others, daily supervision will be necessary.
▪ Before you examine the patient, are there significant medical features of Down’s syndrome that you need to consider immediately?
Yes, there are several, but the one of immediate importance is general joint laxity that involves the atlantoaxial joint. Care must be taken positioning the head and neck to avoid dislocation, which would have severe consequences. In practice this is most likely to affect patients under general anaesthesia or sedation. However, individuals with Down’s syndrome also have poor muscle tone so that the joint is not fully stable even when conscious. Simply ensuring head support, including lateral support, is sufficient. About 15% of patients are affected in this way, though only 1–2% are at high risk of spinal cord compression. Examination of a conscious patient poses minimal risk.
▪ Is the patient able to give consent for the examination?
Capacity to give consent must be assessed in line with the Mental Capacity Act 2005. You need to assess capacity to consent at each visit in relation to the treatment to be carried out. As this individual works part-time in a supermarket and has presented for treatment independently, it is very likely that his consent would be valid for examination but not necessarily for any treatment.
In the meantime, you can proceed with examination and diagnosis.
Examination
Extraoral examination
▪ How can you recognize Down’s syndrome?
Down’s syndrome has a readily recognized physical appearance, characteristic facies and signs affecting the hands that are readily recognized in the dental setting. These include:
• Short stature
• Short neck
• Obesity
• Broad head and sloping forehead
• Round face
• Large lips
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