Mental and behavioral disorders were found among a quarter (23%) of the children with Usher syndrome. The types of disorders observed were not uniform and included atypical autism, mental retardation, schizophrenia, and conduct disorder. The number of individuals found with schizophrenia in this study (1 child) is congruent with results reported by Nuutila [15
] and Grøndahl and Mjøen [14
] using samples of 133 and 89 adults with Usher syndrome, respectively. Among the children without mental and behavioral disorders around one third was found to have psychosocial difficulties. All together, 11 children (42%) faced neither mental and behavioral disorder nor psychosocial difficulties.
Two major explanations for a higher incidence of mental and behavioral difficulties among children and adults with Usher syndrome can be stated. 1) Some argue that the progressive loss of vision results in severe stress and symptoms of mental and behavioral disorder. Case-studies report that mental and behavioral symptoms in patients with Usher syndrome developed simultaneously to the loss of vision. It has been suggested that they are reactive symptoms to severe stress [5
]. In addition to stress-related responses imposed by progressive loss of vision, dual sensory loss may be associated with a higher prevalence of mental and behavioral disorders because of severe communicative difficulties [29
]. Among adults with acquired deafblindness McDonnall [30
] found that communication and social support was important in order to avoid the experience of depression. The communicative difficulties caused by the dual sensory loss, increase the risk of depression. Intervention by means of communication and language rehabilitation is found to be important in preventing mental and behavioral disorders and psychosocial difficulties. This rehabilitation is also important among children with hearing impairment alone [31
] and people with deafblindness [29
2) The second possible explanation for an association between Usher syndrome and mental and behavioral disorders is that some genes are predisposed to both Usher syndrome and for example schizophrenia [8
]. Studies of families with more than one member with Usher syndrome and schizophrenia support this hypothesis [11
]. But until now, no specific genes or mutations have been reported as being suspected candidates. Mental and behavioral disorders may also be a consequence of brain abnormalities associated with Usher syndrome [8
]. Schaefer and colleagues [40
] found that the measured volume of the brain was significantly smaller compared to normal controls and Koizumi et al. [10
] found a global degeneration of the brain in one case with Usher syndrome and schizophrenia. Similar to the surveys by Nuutila [15
] and Grøndahl and Mjøen [14
] this study found that only some individuals with Usher syndrome had mental and behavioral disorders and the nomenclature of disorders was not uniform. Either different Usher genes are associated with different kinds of mental and behavioral disorders, or another explanation may be the necessary.
A developmental psychopathology perspective [41
] of the dynamic interplay of physiological, genetic, social, cognitive, and cultural influences across time may be useful to understand the heterogenic picture of mental and behavioral disorders among children with Usher syndrome. Given the combination and number of disabilities (hearing, vision and balance), children with Usher syndrome may face more barriers to language, social and cognitive development compared to children with hearing loss alone. Even minor vision impairment may in combination with congenital hearing loss increase the child's difficulties developing useful language abilities. Due to the sum of barriers, children with Usher syndrome may become more vulnerable towards developing mental and behavioral disorders. More research is needed to learn more about this dynamic interplay.
Several authors have asserted that there is an over-diagnosis of autism in persons with sensory impairments [42
]. Communicative impairment in the case of individuals with dual sensory loss is similar to symptoms of autism or mental retardation [45
]. Such symptoms among children with sensory disabilities sometimes disappear, when visual, tactile or oral communication has adequately been developed. This was the case for one of the children in this study.
Assessment and support
Like any other organic or somatic cause to mental and behavioral disorders (for example head trauma, tumour, drug abuse) assessing and treating the vision and hearing impairment is the first step in the case of Usher syndrome. Treatment of mental and behavioral disorders among children with Usher syndrome starts with developing the child's communication to reduce the negative impact of dual sensory loss [29
Assessing mental and behavioral disorders among children with Usher syndrome using traditional tests and diagnostic procedures is often difficult due to the children's dual sensory loss and communication deficiencies [6
]. Monitoring of the child's development is needed from early childhood and throughout adolescence including social, cognitive and communicative functioning in addition to vision, hearing, and balance problems. In Denmark 3-4 deafblind consultants work full time supporting children with Usher syndrome, their families, and professionals at the schools where the children attend. The service is financed by the Danish government.
As estimated this study only included 36% to 65% of the total population of children with Usher syndrome in Denmark, this may result in sampling error. Children with Usher type II and III, with both good vision and hearing, in mainstream schools may not be diagnosed with Usher syndrome before they reach late adolescence and are therefore not known by the national service system for children with Usher syndrome and are not included in this study. These children are probably without any serious psychological disturbances. Similarly, some children with Usher syndrome and severe mental retardation may not be assessed for vision and hearing impairment and therefore also not diagnosed or known by the national service system and thereby not included in this study. Given this possible sample error the population of this study may not be comparable with other populations.
This is a first study of mental and behavior disorders among children and adolescence with Usher syndrome. More research is needed in other populations, using other assessment tools and a control group.