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Elective (or selective) mutism is a rare psychiatric disorder. Diagnostic criteria in both ICD-101 and DSM-IV2 include: (a) consistent failure to speak in specific social situations in which there is an expectation for speaking (for example, at school) despite speaking in other situations (for example, at home); (b) the disturbance interferes with educational or occupational achievement or with social communication; (c) it is not better accounted for by a communication disorder or by a lack of knowledge of the spoken language required in the social situation; (d) it has a duration of at least 1 month.3
It typically starts at preschool age, is more common in girls, and is seen in all social strata with shyness, withdrawal, sensitivity or resistance, and internalising behaviour problems as the most common personality features.
We followed up a 7.5 year old girl who was the third child from non-consanguineous parents. She was born normally at 37 weeks of an uneventful pregnancy, with a birth weight of 3,5 kg, length 47 cm, and head circumference 34.5 cm. The American pediatric gross assessment record was 9 at 5 minutes. Family history was non-contributory. There was neither family history of psychiatric illness nor of language abnormalities.
Developmental milestones were normal; she acquired head control at the 3rd month of life, sat at 7 months, and walked at 13 months. On the other hand, she presented speech delay as she used single words meaningfully as late as 24 months and was able to pronounce her first phrases at 3 years. Behavioural anomalies were first registered by her parents between 3 and 4 years, when they noted a reluctance to speak in front of other people. By the age of 4, she used to speak regularly only to one her friends, and she did not talk to nursery staff or to other children. At home, she normally spoke to her parents and her sister but would not speak to them in front of others.
She first came under our care at the age of 6 years. Physical examination showed a pattern of facial dysmorphisms involving flattened nasal bridge, short upper lip, broad philtrum, everted lower lip, and micrognathia. Short and broad fingers were also noted. Muscular tone and deep tendon reflexes were normal. No abnormal pyramidal, extrapyramidal, or cerebellar signs were present. She had no dyspraxia. Her height was below the 10th percentile, weight on the 15th percentile, and head circumference on the 10th percentile.
The autism diagnostic interview,4 5 administered by her mother, showed a score of 9 in the area of communication (cut off level of 8), but she scored 6 in the areas of qualitative impairments in reciprocal social interaction (cut off of 10), and 0 in repetitive behaviours and stereotyped patterns (cut off of 3). Social and imitative play seemed inadequate, but no language abnormalities such as echolalia, neologisms, or pronominal reversal were present. Her social interactions were reciprocal although she usually only smiled at her parents, did not have easy peer relationships, and directed no language towards the hospital staff. However, she was able to engage in good eye contact. Clumsy attempts to interact with other children where made by the patient when she was not directly observed by medical stuff.
The patient was also evaluated by the Wechsler intelligence scale for children which showed a performance IQ of 79, and verbal IQ of 70.
Biochemical tests for aminoacidopathies, mucopolysaccharidosis, and lysosomal disorders were normal, as was selective screening for organic acidaemias. An isoelectric focusing test for sialotransferrine was normal. Molecular tests for fragile X syndrome were negative. Brain MRI examination, EEG recording, and audiometric tests were normal. Karyotype analysis of blood cells showed an abnormal chromosomal pattern with deletion of the short arm of chromosome 18, 46XX, del(18), p(11.1) in all metaphases examined. Karyotype analysis was normal in her parents.
Simons et al recently reported the first patient affected by elective mutism associated with deletion of the short arm of chromosome 18, del (18), p (11.1).3 Their patient had had developmental abnormalities but these could not account for her social communication disorders, and peculiar dysmorphisms were present.We also had the opportunity to study a girl affected by elective mutism in whom karyotype analysis showed an identical deletion of the chromosome 18. Speech delay, facial dysmorphisms such as flattened nasal bridge, broad philtrum, and micrognathia were the main clinical findings. Auxological indices were in the low average range; particularly, skull circumference was on the 10th percentile. No familiar trait of microcephaly was present in her family, and short stature appeared when the height of our patient was compared with the midparental height (data not shown). Psychological testing showed verbal skills and performance in the low range (table). We compared our patient with the one reported by Simons et al (table).3 With the exception of the round face, not seen in our patient, clinical findings of both patients overlapped. Moreover, both patients had speech delay, a similar neuropsychological profile, and the same 18 chromosome abnormality. All these findings allow us to hypothesise that the association of such signs is not by chance and it may be indicative of a distinct clinical entity.
Elective mutism is most probably a heterogeneous syndrome and several aetiological factors such as minimal brain dysfunction, somatic or psychological trauma, particularly during speech development, and a particular family structure especially the mother-child relationship, have been suggested. As a consequence clinical features are variable and speech delay and dysmorphisms can be found in a subgroup of patients only.6 Moreover, in most patients elective mutism is a transient disorder as it usually disappears in a few months. By contrast, in our patient as well as in the one reported by Simonset al, elective mutism appears as a chronic disorder and it has been affecting our patient for about 4 years. Therefore, we think that in a subgroup of patients elective mutism is related to a genetic background. This hypothesis is further corroborated by the study of Steinhausen et al, who pointed out that genetic factors play a part in the aetiology of selective mutism, as they found that disorders of speech, language, and psychiatric illness were more common in the relatives of affected than in the control groups.7
Deletion of the short arm of chromosome 18 has also been associated with several phenotypic expressions, mental retardation, and autism.8 9 However, in our patient diagnosis of elective mutism was firmly made as autism or connected pervasive developmental disorder were ruled out because of social disorders which were highly specific and situational.
In conclusion, we confirm that the relation between elective mutism and deletion of the short arm of the chromosome 18 is not by chance, and think that their association with developmental disorders and dysmorphisms, occurring in these patients, may delineate a specific clinical entity.
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