The causes of profound deafness in childhood : a study of 3,535 individuals with severe hearing loss present at birth or of childhood onset / George R. Fraser.

  • Fraser, George R. (George Robert)
Date:
[1976], ©1976
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: The causes of profound deafness in childhood : a study of 3,535 individuals with severe hearing loss present at birth or of childhood onset / George R. Fraser. Source: Wellcome Collection.

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    somewhat anomalous in that profound childhood deafness in general is known to affect males more often than females (see Chapters VI, XII, and XIII). The lack of an excess of males among the adults in the Oxfordshire and Berkshire study is not due to preferential inclusion of males among the 180 surveyed, since the total of 377 deaf adults in the area (see page 3) is also almost equally divided between males and females; in South Australia, on the other hand, the ascertainment was almost complete. The explanation for this equal distribution between the sexes may lie, at least partly, in the generally better life expectancy of females (thus, in the Oxfordshire and Berkshire survey, there were 18 females and only 12 males aged over sixty years), but in any case it is clear that, especially in view of the small numbers involved, inequalities of the sex ratio and, specifically, a male excess, cannot be expected to be helpful in collective allocation of cases to acquired causes. The difficulties are compounded by the fact that information about the perinatal period and about disease in infancy and childhood was unobtainable in a large percentage of these adults, especially in the older age groups, where the parents were no longer alive; even birth weights were available in only a small number of cases. It is, however, probable that perinatal causes do not play such a large part in the causation of deafness among these adults, since these causes have been gaining in prominence relatively recently, presumably owing to increased survival of infants who have passed through a turbulent neonatal period (see Chapter XII). There is limited evidence that a few cases of deafness due to undetected prenatal rubella are included in the group of unidentified cause, in that this group contains a disproportionate number of persons born between 1940 and 1944, which are the years when the majority of cases due to rubella embryopathy were born (see Table XI-5). Thus, excluding cases of deafness which is known to be due to rubella, of 27 adults born in this period, 13 (48 percent) were in the group of unidentified cause, whereas for those born between 1887 and 1939 this proportion is 41 out of 129, or 32 percent. The majority of the 26 persons in the residual group of unidentified cause probably owe their deafness to causes acquired after the end of the perinatal period. As well as meningitis, which is such an important cause among the children of the present survey, some cases due to chronic otitis media are also likely to be included, since this was an important cause of profound childhood deafness before effective medical treatment became the rule; it should be noted that this cause is not associated with an excess of males (see page 275). Tentatively, therefore, the 26 cases in the residual group of unidentified cause may be allocated to acquired causes as follows: 4 prenatal, including rubella (2 males, 2 females); 6 perinatal (3 males, 3 females); and 16 (6 males, 10 females) acting after the end of the perinatal period. The complete tentative allocation of the group of unidentified cause is shown in Table XIV-11. Adults in South Australia. The group of unidentified cause consists of 104 persons (48 males and 56 females). Cases 330-89 of Table IX-11 may be used in a segregation analysis to determine the number of simplex cases which can be subsumed under the hypothesis of recessive inheritance; cases 390-92 are not of relevance, even though hearing loss is autosomal recessive, since these are the offspring of deaf parents. Cases 330-89 consist of 32 males and 28 females; 49 are multiplex and 11 simplex. A segregation analysis shows, using a ratio of affected to total sibs of 0.225, that 19 simplex cases coming from sibships of more than 1 can be subsumed under the hypothesis of recessive inheritance, or allowing for the 8 cases coming from sibships of 1, 21 cases in all. This would give a ratio of simplex to multiplex cases of 32 to 49, or 0.65, which is very low, even allowing for the large average family size among South Australian adults. Application of a value of 1.42 for this ratio, as used for the children in this survey (see