Cognitive, adaptive, and behavioral features in Joubert syndrome

Participants

Fifty-four patients (35 males, 19 females; age range: 10 months to 29 years; median age: 8 y 5 m; mean age: 9 y 11 m; standard deviation: 6 y 6 m) including one pair of twins, four pairs and one trio of siblings, were selected between 2007 and 2010 by Italian Scientific Institutes and Universities specialized in diagnosis and management of subjects with JS. Table I shows maternal education and parental job according to the coding system of Italy's National Statistics Institute for all subjects [ISTAT, 1991].

MRIs were reviewed by neuroradiologists experts in cerebellar malformations, including members of the Italian Joubert syndrome group, and the “molar tooth sign” was confirmed in all subjects. A pathognomonic combination of imaging findings on axial MRI was found in all patients, that is, cerebellar vermis hypoplasia, thickened and horizontally oriented superiori cerebellar peduncles, and a deep interpeduncular fossa (the molar tooth sign) [Poretti et al., 2014]. Other CNS anomalies were present in two subjects (one corpus callosum abnormality and one polymicrogyria).

Further clinical and instrumental details were obtained through the referring clinicians using a standardized questionnaire, that allowed classifying patients into six clinical subgroups [Romani et al., 2013]: pure JS (n = 20), JS plus retinal disease (n = 18), JS plus renal disease (n = 5), JS plus retinal and renal disease (n = 1), JS plus liver disease (n = 5), and oro-facio-digital syndrome type VI (n = 5). The developmental data and clinical signs are outlined in Supplementary Table SI.

Organ involvement was assessed by clinical examinations and instrumental testing as appropriate, including inspection of fundus oculi, visual evoked potentials, electroretinogram, abdominal ultrasound, routine renal parameters, urinary specific gravity, urinary concentration test after desmopressin stimulation, and liver biopsy. All patients underwent next generation sequencing-based target resequencing of the 26 JS causative genes known at the time of the experiment (as part of a panel of 120 ciliary genes) on a Solid 5500xL platform. Thirty-two patients were found to carry homozygous or compound heterozygous pathogenic mutations in the following genes: TMEM67 (9), CC2D2A (4), INPP5E (4), AHI1 (4), RPGRIP1L (2), NPHP1 (1), CEP290 (2), KIAA0586 (1), TMEM237 (1), TMEM216 (2), TMEM17 (2). In 23 patients, biallelic pathogenic mutations could not be detected in any of the tested genes. Nine of them were found to carry a single heterozygous mutation in a JS-causative gene (CEP41, C5Orf42, KIAA0586, CC2D2A, INPP5E, NPHP1, TCTN1, ARL13B) whose significance remains to be established.

Developmental/Neurological and Neuropsychological, Adaptive, and Behavioral Assessment

Statistical Analysis

SPSS 10.0 for Windows was used to analyze all data.

The Wechsler intelligence scales, the Leiter or Griffiths mental development scales were used to determine the intelligence quotient (IQ) or general quotient (GQ) scores. Raw scores in adaptive scales were converted to age-equivalent scores and then to ratio Quotient (rQ) scores, so that performances on different tests in the same subjects and between groups of subjects could be compared. The rQs were calculated by averaging the equivalent ages on all subtests to obtain mental age, then dividing it by chronological age and multiplying it by 100.

All statistical tests were two-tailed and P-values of 0.05 or lower were considered significant.

A repeated measures ANOVA was used to analyze the intelligence/developmental scales, the CBCL, and the VABS to detect significant difference among the means. Bonferroni corrected post hoc tests were performed to discover which specific means significantly differed between pairs of tests.

The t-test was used to compare the scores of two groups (independent sample) or two performances within the same sample (paired sample).

Pearson correlation test was performed to analyze the relationship between cognitive and behavioral scores, as well as between the cognitive-behavioral scores and chronological or equivalent age.

Developmental and Clinical Features

A global developmental delay was found in 44 (81%) patients. This is a condition of significant delay in developmental milestones at expected ages in two or more of the following domains: gross/fine motor, speech/language, cognition, social/personal, and daily life activities in children younger than 5 years old [Shevell et al., 2003].

Thirty-six (about 66%) subjects learned to walk independently well-enough to get around outside their home, but all developed ataxia with a broad-based, unsteady gait, and had difficulties in running or climbing stairs. Acquisition of independent walking was delayed from 15 months to 9 years (Mdn: 24 months). At testing, eight subjects did not walk independently (three were still younger than 2 years old), three were only able to take a few steps autonomously, five walked with caregivers’ support (three have a severe visual deficit), and two required assistive equipment for mobility (walker and wheel chairs, respectively). Forty-five subjects were verbal. The first words of the verbal subjects were uttered between 10 months and 10 years (Mdn: 24 months), and seven had not yet achieved the ability to associate words (two were younger than 3 years old). Word association was achieved between 15 months and 7 years 4 months (Mdn: 36 months) in 25 patients. Further information is displayed in Supplementary Table SII.

Although variable in severity, dysarthria was found in 40 of the 45 verbal subjects; only five subjects showed good speech articulation.

Additional neurological signs were hypotonia (42.6%), ataxia (87%), and eye movement abnormalities, including nystagmus, strabismus, and ocular motor apraxia (74%). Seizures were rarely noted (3.7%). Altered respiratory patterns characterised by short alternate episodes of apnoea and tachypnoea or episodic tachypnoea alone were found in 31.5%.

Associated clinical features included ocular signs (retinal dystrophy 40.7%; colobomas 13.0%), renal signs (kidney dysplasia 7.4%; nephronophthisis 11.1%), liver signs (liver fibrosis 7.4%; high transaminases 12.9%). Facial dysmorphisms, including prominent forehead, ptosis, prognathia, arched eyebrows, lower lip eversion with trapezoid-shaped mouth, and tongue protrusion were noted in 68.5% and polydactyly (hands or feet) in 18.5%. Table I summarizes the occurrence of multiorgan involvement, and Supplementary Table SI shows clinical data for each subject.

Cognitive, Adaptive, and Behavioral Results

Correlations with age

The chronological age of patients with JS correlated with the equivalent age in intelligence/developmental (r = 0.815; P < 0.001), and adaptive tests (r = 0.548, P < 0.001 for Communication; r = 0.575, P < 0.001 for daily living skills; r = 0.573, P < 0.001 for socialization).

Figure 1 shows the scatterplots of the correlation between chronological age and developmental age obtained in cognitive and adaptive scales.

Intelligence

Intellectual functioning was found to be remarkably variable, with Full IQ scores ranging from 32 to 129, excluding five unassessable subjects. It is well substantiated that cognitive and emotional functioning of children with JS is often difficult to assess due to impaired fine/gross motor movements, abnormal eye movement, and speech control, all causing barriers to interaction, active communication, and appropriate emotional display [Ziegler et al., 1990] with the inevitable outcome that severe intellectual disabilities are overgeneralized [Hodgkins et al., 2004]. The first clinical studies highlighted severe motor, intellectual, and social disabilities; however, formal cognitive assessments had not been used [Boltshauser and Isler, 1977; Curatolo et al., 1980; Aicardi et al., 1983; Gitten et al., 1998; Kumandas et al., 2004]. Most clinical studies still confirm that developmental delays and intellectual disabilities are key features of the syndrome [Romani et al., 2014], and to date patients with JS with normal IQ have rarely been reported [Gunay-Aygun et al., 2009; Poretti et al., 2009; Romani et al., 2014]. The present study demonstrates a normal or borderline cognitive functioning in up to 28% (15/54) patients, a proportion that is much higher than expected. The reliability of the assessment is ensured by the expertise of neuropsychologists, working in centers specialized in the diagnosis and management of patients with JS, and by the use of tools with standardized methods of administration and scoring. Such a high percentage of normal or borderline IQs could stem either from the examination of a large sample, allowing for better detection of the heterogeneity of cognitive profiles, or from the increasing capacity to diagnose also those subjects with a very mild phenotype. Furthermore, 7 of the 15 subjects with IQ within the normal range were evaluated with Leiter-R due to the presence of serious language/speech disorders; in these patients, verbal impairment may hinder the adaptive capacity regardless of preserved IQ; if assessed with inadequate tests, these patients might have been misclassified as intellectually disabled.

Intellectual disability was found in 72% (39/54) of patients, and thus continues to represent a hallmark of the syndrome but cannot be considered a mandatory diagnostic criterion of JS. The profiles obtained by Leiter-R and Griffiths developmental scales were homogeneous, while the Wechsler scales showed significant differences among both verbal and performance subtests. The arithmetic and comprehension items were weak points of verbal functioning, with relative preservation of reasoning by similarities, and coding was a weak point on performance tasks. These findings seem to confirm, on a wider sample, the specific peaks, and valleys profile found in four patients with JS by Tavano and Borgatti [2010]. In accordance with the freedom from distractibility factor by Kaufman [1979], the low scores in arithmetic and coding may be interpreted as a working memory deficit and an impairment in the capacity to provide temporary storage and manipulate information, as confirmed by the correlation with digit span on the Wechsler scales. As the coding score was not significantly correlated with the VABS motor rQs, this would indicate that poor performance in the task was due to a difficulty in managing double tasks rather than a motor deficit.

Adaptive Behavior

The VABS showed that motor organization was the area of vulnerability of the adaptive functioning profile, its quotients being significantly lower than both the ABC (sum of communication, daily living, and socialization domains) and the cognitive scores (Wecshler and Leiter-R IQs, and Griffiths GQ). It may be that motor disabilities could affect all other areas of adaptive behavior, possibly limiting the acquisition of personal care (hygiene and getting dressed), social (play and sport autonomy), and scholastic (drawing and writing) skills.

On the contrary, the communication rQ was higher than the daily living and socialization rQs, confirming the clinical evaluation of patients with JS as effective and discrete communicators, despite their language impairment, ranging from its complete absence, to an understandable speech. The patients’ communicative skills in the daily context appear relatively preserved as they are sustained by communicative intentionality, good interaction with the environment, and attention to others’ verbal messages [Braddock et al., 2006].

Emotional and Behavioral Functioning

The results indicate quite good emotional and behavioral functioning in subjects with JS. Most children did not show maladaptive behaviors consistent with a psychiatric diagnosis. Four patients met the criteria for a DSM-oriented psychiatric diagnosis (i.e., two oppositional defiant and two bipolar disorders), and two showed the triad of symptoms typical of the autistic spectrum disorder (i.e., absent verbal communication, impairment in reciprocal social interaction, stereotyped and repetitive behaviors) associated with severe intellectual disability, unassessable with standardized testing, and sensory and motor disabilities, constituting a very complex picture. The percentage of psychiatric diagnoses in our JS group (7.4% or 11% including the two subjects with autistic-like symptoms) is consistent with that of large cohort studied by Bachmann-Gagescu et al. [2015] in which 47 subjects (8.8%) showed a variety of mental health problems such as anxiety, aggression, depression, and autism. Our findings are in disagreement with the studies reporting a high prevalence of autism in JS [Holroyd et al., 1991; Ozonoff et al., 1999], but are in line with Takahashi et al.'s [2005] hypothesis that JS is a genetically distinct disorder from autism. These authors found that, on 47 children with JS evaluated with the autism behavioral checklist, no child met the clinical cut-off for autism (parents’ symptom report), and that only 4 out of 32 exhibited clinically significant borderline symptoms of autism, with an overall profile more similar to the one expected for developmental delay. Steinlin et al. [1997] previously described 16 children with JS as pleasant, friendly, easy to guide, and socially included, although some had a tendency to react in a mildly aggressive manner when their handicap was pushing them to their limits. Moreover, the verbal children of the Steilin's group had relatively spared communicative skills even if they produced only simple sentences with flat prosody and hoarse voice. More recently, Braddock et al. [2006] also confirmed that patients with JS typically had verbal and tongue apraxia with reduced speech control, but showed good communicative skills including effective gestures, particularly in those with less intelligible language. Overall, it can be concluded that patients with JS did not show classic symptoms of autism spectrum disorder.

Although psychiatric diagnoses are rare, a subset of approximately 40% displayed inattention, hyperactivity, social withdrawal, and atypical behaviors that affected parents’ ability to manage the child's physical and emotional needs. The prevalence of behavioral and emotional problems detected by the CBCL is very high when compared to typically developing Italian children [Gritti et al., 2014] and adolescents [Frigerio et al., 2009], but not when compared to populations with neurodevelopmental disorders, such as intellectual [Masi et al., 2002] and learning [Capozzi et al., 2008] disabilities. In our sample, internalizing problems (anxiety/sociality) were confirmed as common, and the CBCL total score was negatively correlated with the level of global social adaptive functioning. It seem to suggest that emotional and behavioral problems impact on the patients’ adaptive behavior, in particular reducing the social competence and daily-life independence, consequently increasing the perceived parental stress in everyday management [Farmer et al., 2006]. This result is an interesting and novel finding that needs to be confirmed in other larger JS cohorts.

Developmental Approach

An interesting result was the positive correlation found between chronological and equivalent age on cognitive and adaptive behavior tests. Although in presence of slow, progressive improvement, these findings can be considered developmentally as a continuum with gradual acquisition of new skills until adulthood. This interpretation refutes the conclusions of some long-term follow-up studies on patients with JS which suggested that motor and cognitive deterioration occurs across their life span [Cantani et al., 1990; Gitten et al., 1998], while it is consistent with the conclusions of Tavano and Borgatti [2010] and with the data on single cases reported by Ziegler et al. [1990]. Also Romani et al. [2014] reported two cases of patients with severe developmental delay until 5 years of age, who, at later follow-up, showed unexpected and exceptional mental abilities. As these data are cross-sectional, a longitudinal study needs to confirm these observations.

Our data also suggest that there is discontinuity between developmental delay and intellectual disability [Shevell et al., 2003]. In fact, five out of eight subjects with a clinical history of normal global development were later diagnosed by us with intellectual disability, conversely 12 out of 15 children with normal IQs at our testing had a history of global developmental delay.

Limitations

Variability in the cognitive and behavioral phenotype is very common in genetic syndromes, especially during development.

The daily clinical work demonstrates to neuropsychologists and child neurologists that it is necessary to choose the best possible tool for each patient, that is, that can describe cognitive and behavioral functioning with more effectiveness. This attention in individualizing the assessment implicates that it is impossible to use a unique test, which constitutes a clinical strength but a methodological limitation.

However, the wide range of age, the different degrees of sensorial impairment and the severity of intellectual disability within 54 subjects with JS required the use of different tools for the collection of intelligence data.

The correlations between the cognitive/behavioral profiles and the genetic causes of the disease is not applicable because the genotype is not fully defined yet [Romani et al., 2014]. To date, biallelic mutations in about 30 genes, all involved in primary cilium biology, are known to compose the genetic spectrum of JS. However, the genetic cause remains unidentified in nearly 40% of JS-affected individuals [Bachmann-Gagescu et al., 2015], and the neuroradiological identification of the molar tooth sign still remains the diagnostic tool for JS [Romani et al., 2013; Poretti et al., 2014].