ANNOTATIONS

child with learning problems must assess his ability to handle the integration of several simultaneous stimuli.

Tests involving crossmodality and intermodality transfers between various sensory stimuli are relevant to the analysis of the process by which learning goes on. The ability to tune out irrelevant stimuli is an additional measure of the organism’s integrating ability. The face-hand and sound-touch tests are examples of tests of the child’s ability to acquire the necessary ‘set’ and to tune out what is not relevant. The child who cannot learn new materials and change ‘set’ in a clinical setting is likely to find difficulty in a comparable school setting.

A structure, stability and consistency in the world as he perceives and understands it, and some freedom from distracting stimuli, are necessary for the adequate development of mentation in children. Children with brain dysfunction, relatively poor previous training or both need to acquire an explicit awareness of the physical qualities of the environment. They need to be taught in small classes, with few distractions and greater structure.

OZER uses the term ‘operant conditioning’ to mean a discipline in which the learning process is made more explicit by breaking down a learning task into a series of small steps. In programmed instruction the first step is one to which the child can respond as it is already within his repertoire. Each successive step leads on from this so that there is a gradual alteration of the child’s set. At each step reinforcement is provided to maintain the acquired behaviour and so make the next step possible. If the child cannot make the next step it is broken down into smaller steps which he can make. OZER describes the process by which these successive steps are formed and transferred-that is, the process of ‘fading’. In operant conditioning the reinforcements necessary for learning are carefully analysed so that there is greater awareness and manipulation of the good reinforcers. Explicit awareness of the mental techniques which make learning possible, and of the meaningful reinforcers, would supply the means of more adequate assessment of potential levels of performance. Many psychological tests tend to assess present levels of performance. The differential rate of learning of children under standardised optimal conditions would be a fairer measure of the child’s true potential. In young children the possibilities of adaptation to the brain damage by repair and maturational growth may modify within certain limits the degree of loss of function. The extent of brain dysfunction as determined by various neurological measures may help to define those limits of adaptation, but one must probe to the limits of the child’s function to determine more accurately his potential functional capacity. We need to make our methods of evaluation reflect possible gain rather than present performance.

J. FRANCIS-WILLIAMS Griffins, Abinger Hammer, Nr. Dorking, Surrey.

REFERENCE 1. Ozer, M. N. (1966) ‘The use of operant conditioning in the evaluation of children with learning

problems.’ Clin. Proc. Child. Hosp. (Wash.), 22, 235.

DOWN’S SYNDROME AND PARENTAL CONSANGUINITY IT has been known for many years that mongols tend to be born to elderly mothers. I t has been estimated that about two-thirds occur through some cause connected with the ageing process in the mother and one-third from various causes that are independent of maternal

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age. This maternal-age-independent class would include, for instance, mongols born to mongol mothers, those with a balanced translocation carrier as one parent, and some mosaic mongols. However, only a small proportion of mongols born to younger mothers are accounted for in this way. Most are standard trisomic mongols born to parents with normal chromosome complements.

Mongolism independent of maternal age might be due to such exogenous factors as viral infection or irradiation, or to genetic factors. PEN ROSE^ suggests that man might have recessive genes which tend to cause non-disjunction in the ova of homozygous females, as is known to happen in drosophila. If there was a rare recessive gene acting in this way one would expect to find a raised consanguinity rate in the maternal grandparents (these would be heterozygous for the gene and some of their children would be homozygous).

Several investigations have now been undertaken to test this hypothesis. FORSSMAN and ~ E S S O N ~ analysed 1,344 cases of Down’s syndrome in Sweden, determining whether (a) the subject, (b) the subject’s father and (c) the subject’s mother were or were not the offspring of first cousins. An experienced genealogist was employed to organize a search for the data required from the parish registers and central archives. The authors found no difference in consanguinity rates between the ascendants of their subjects and the general population. BERG’ compared the parental consanguinity rates of mongol and non-mongo1 mentally subnormal subjects in the London area and found that the mongols did not differ in this respect from the general population.

MATSUNAGA~ investigated 104 children with Down’s syndrome born to younger mothers in Japan, where the consanguinity rate of the general population is high, and did not find any higher rate in the mothers of his subjects.

In an inbred population the consanguinity rate is high. If, therefore, a rare recessive gene predisposing to non-disjunction was present in the genotype the proportion of subjects homozygous for it would be increased in such a population. This might raise the incidence of Down’s syndrome and lower the mean maternal age at birth. KWITEROVITCH et aL4 investigated an inbred population of 10,OOO in a settlement in Ohio, U.S.A. They ascertained 17 mongols, an incidence of 0.16 per cent, with a mean maternal age at birth of 35.9 years. The incidence accords fairly closely with those of other, outbred, populations. The authors also quote the survey of JUBERG and DAVIS3 in a neighbouring inbred settlement, in which 16 trisomic mongols were ascertained and there was no evidence of a genetic factor.

The present evidence suggesting a genetic factor in Down’s syndrome is (I) the occurrence of familial cases with more than chance frequency and (2) the occurrence of trisomy in different members of the family, involving different chromosomes, also probably with more than chance frequency. Thus a genetic factor in non-disjunction cannot be excluded, but no convincing evidence of it has yet been produced.

St. Lawrence’s Hospital, Caterham, Surrey.

REFERENCES 1. Berg, J. M. (1967) Discussion to paper of Forssman and Akesson.2 2. Forssman, H., Akesson, H. 0. (1967) Consanguineous Marriages and Mongolism. In Mongolism. Ciba

3. Juberg, R. C., Davis, L. M. (1966) ‘Etiology of non-disjunction: Lack of evidence for genetic control.’

4. Kwiterovitch, P. O., Cross, H. E., McKusick, V. A. (1966) ‘Mongolism in an inbred population.’ Bull.

5. Matsunaga, E. (1966) ‘Down’s syndrome and maternal inbreeding.’ Acra Genet. nied. (Ronru), 15, 224. 6. Penrose, L. S. (1967) Discussion to paper of Forssman and Akesson.2

B. W. RICHARDS

Foundation Study Group No. 25. London: Churchill.

(Abst.) Soe. pediat. Res. Program & Abst., 105.

Johns Hopk. Hosp., 119, 268.

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