Summary of the lecture delivered at the yearly meeting organised in October 1995 by the “Werkgroep Dystrophia Myotonica” for patients and other people involved in myotonic dystrophy. This lecture was prepared by S. Umans, J Steyaert and D. Willekens of Stichting Klinische Genetica Limburg, Maastricht and Centrum voor Menselijke Erfelijkheid, U.Z. Gasthuisberg, Leuven.
The authors distinguish different types of myotonic dystrophy. Depending on the age when muscle complaints and other associated symptoms make their first appearance, they distinguish:
1) The mild type: often cataract is found at a relative young age without occurrence of other complaints.
2) The adult type affected with myotonia at adolescent age and having increasing muscle dystrophy between the age of 20 and 40 years.
3) With the juvenile type the patient as a child already has muscle-complaints and besides has learning- and speech-defects.
4) The early infantile type distinguishes itself from the juvenile type by the presence of light symptoms from birth on. These children show similarly to the congenital type feeding problems during their first year of life, in a lighter degree than the congenital type: Development difficulties (motor development, language, speech and learning difficulties at school).
5) The congenital type: the baby clearly suffers from serious muscle-weakness, as demonstrated by lack of foetal movements, problems with swallowing and respiratory problems at birth.
DESIGN OF THE RESEARCH PROGRAMME
Among adults having the adult type of myotonic dystrophy several studies were performed regarding intelligence and occurrence of depressions. The results prove that a number of persons with myotonic dystrophy have a lower IQ than expected. On the other hand up till now little literature is available dealing with the early infantile and the juvenile type and concerning the cognitive functioning and the possible emotional difficulties.
Therefore in Leuven and Maastricht in the centres for clinical genetics a research programme was started which probes for possible behaviour, learning and emotional difficulties within a group of children and adolescents having the congenital type, the early-infantile type and the juvenile type of myotonic dystrophy.
Up till now 8 girls and 7 boys between 7 and 18 years of age, were examined. Eleven of them were in their families the first known patients suffering from myotonic dystrophy; all of them were referred to the centre for clinical genetics because of a great variety of clinical problems. The remaining 4 children were their siblings and they themselves had some type of myotonic dystrophy.
Of these 15 children 3 had the congenital type, 5 had the early-infantile type and 7 had the juvenile type.
Within the group of the early infantile type the learning difficulties often were the first signal that alarmed the parents, thus causing diagnosis of myotonic dystrophy being made during the first years in the elementary school.
The intelligence was examined by the IQ-tests WISC-R or WAIS depending on their age. These intelligence tests examine the VIQ (Verbal Intelligence Quotient, this is the intelligence for which the language is needed) and the PIQ (Performance Intelligence Quotient, thinking with use of spatial insight without need of language). It is important to know that the average IQ of the population is 100.
Possible behaviour difficulties were investigated with the CBCL (Child Behaviour CheckList); this checklist was completed by the parents. It is a checklist with several items dealing with behaviour difficulties; the degree of occurrence is counted.
Possible occurrence of depression was examined in the older children by self-report questionnaires.
Children older than 12 years of age were asked to complete the Adolescent Temperament Questionnaire. This questionnaire produces a profile of and a rough idea on the temperament.
To investigate the occurrence of certain psychiatric problems typically related to children, their parents were interviewed with the help of a structured child-psychiatric interview: the Amsterdam Child-psychiatric Interview for Children and Adolescents (ADIKA), a Dutch version of the American DICA-questionnaire.
The IQ’s of the subjects were between 50 and 95, with an average figure of 80. This figure is clearly below 100, the average IQ in the population. No clear difference could be established between the verbal and the performance part of the intelligence. The difference in disadvantage of the performance IQ, as found in some studies on adult patients with myotonic dystrophy, was not again found in this study of a small group of children.
Observations during the tests showed with 10 out of the 15 subjects concentration difficulties and a brief space of attention-time. In some children also other cognitive deficits were found ( among others: defects in spatial analytical thinking, wrong thinking-strategy etc.)
CHILD BEHAVIOUR CHECKLIST CBCL
The CBCL showed behaviour difficulties in the so-called clinical range in 5 out of 15 children. Particularly withdrawal, social problems and attention-deficits were often found through this checklist. Four of these children present a child-psychiatric disorder.
With children with problems in accordance with the CBCL the internalising complaints (fearful, reserved, depressive) dominate the externalising complaints (hyperactive, oppositional, aggressive).
Two children showed depressive complaints on the depression-scale. Both these 2 children as some others, had to face several problems during their school-career: Low results from the beginning of the elementary school, being bullied and transfer to special education. These events represent important psychosocial stress factors, which can cause depressive complaints.
The results on the Adolescent Temperament Questionnaire were varying and showed no specific profile.
The child-psychiatric interview showed with 9 out of the 15 subjects child-psychiatric problems. This figure is substantially higher than the figure found in the population.
Five children had Attention Deficit and Hyperactivity Disorder (ADHD). This is a disorder with the symptoms: concentration and impulsivity deficit and hyperactivity. In the whole group parents often mentioned impulsive behaviour and attention deficits, even in children who did not meet all the criteria for Attention Deficit and Hyperactivity Disorder.
Two children had a separation-anxiety disorder (difficulties with loosening themselves from their parents, which manifests itself in unruly behaviour at moments of separation and continuing concern about and fear of loosing their parents or that they will be harmed.
One child had a general anxiety disorder (extreme concern, afraid of making mistakes and fear connected with events in the future and past)
One child had an adjustment disorder with depressive mood, which is a result of poor performance at school and being bullied.
For the time being it is premature to jump to conclusions based on this research in this small group. The results of the assessment of the intelligence confirm earlier research in adults with the adult type of myotonic dystrophy. This research showed that several persons with myotonic dystrophy have a lower IQ than the population- mean. Besides, some children with myotonic dystrophy have attention deficits which interfere in their functioning at school.
Striking in this pilot study is the frequent occurrence of child-psychiatric disorders. It must be mentioned that these results were obtained by means of structured interviews. At the same time most children were in their families the first known patients having myotonic dystrophy, which means that within the group there were lots of physical problems. Within this context we should interpret these results.
It has to be stated that these findings should be checked within a larger group of children and the findings should be compared with a group of children suffering from another chronic disease before we can get more decisive conclusions.