Rett syndrome--distribution of phenotypes with special attention to the preserved speech variant

The Rett Syndrome Complex

Communicative functions and their relationship with overall developmental level and autistic features were studied in eight young women with disorders in the Rett syndrome complex, three with the classical variant and five with variants with partially preserved/regained speech. The Vineland Adaptive Behaviour Scales, individual structured observation, and a specially designed structured interview covering early pre-linguistic and linguistic development, current receptive and expressive language and non-verbal communication skills, were used. Autistic features were evaluated in accordance with the DSM-IV. Low levels of communicative abilities and overall functioning were demonstrated. In most cases, the communicative abilities did not reach the level expected on the basis of overall development. Joint attention behaviours and expressions of communicative intent were rare. However, six of the eight subjects showed clear examples of social interaction abilities.‘Eye pointing’, as distinct from ‘eye communication’, was demonstrated only in a minority of the cases. The level of communicative function at developmental arrest did not predict later language ability. It is suggested that intervention should focus on developing further the joint attention behaviours, intentional communications and communicative functions spontaneously used by individuals with disorders in the Rett syndrome complex.

Rett Syndrome: Coming to Terms with Treatment

Rett syndrome (RTT) has experienced remarkable progress over the past three decades since emerging as a disorder of worldwide proportions, particularly with discovery of the linkage of RTT to MECP2 mutations. The advances in clinical research and the increasing pace of basic science investigations have accelerated the pattern of discovery and understanding. Clinical trials are ongoing and others are planned. A review of these events and the prospects for continued success are highlighted below. The girls and women encountered today with RTT are, overall, in better general, neurologic, and behavioral health than those encountered earlier. This represents important progress worldwide from the concerted efforts of a broadly based and diverse clinical and basic research consortium as well as the efforts of parents, family, and friends.

Atypical features in MECP2 P152R-associated Rett syndrome

BACKGROUND

Rett syndrome is a neurodevelopmental disorder that occurs in individuals with a mutation in the X-linked methyl-CpG-binding protein 2 (2MECP2) gene. 2MECP2 mutations produce a high degree of variability in the clinical phenotypes including the classic Rett features of head growth deceleration, psychomotor regression, deviant communicative ability, hand stereotypes, autonomic dysfunction, and seizures. Atypical forms of Rett such as those with preserved speech do not follow these characteristics.

PATIENT

We report a 9-year-old girl with atypical Rett (macrocephaly, preserved speech, and psychiatric manifestations) with a 2MECP2 (P152R) mutation that generally is not associated with these clinical signs.

CONCLUSION

This case broadens the genotype-phenotype correlation between the P152R mutation 2MECP2-associated Rett syndrome.

Diagnostic criteria for the Zappella variant of Rett syndrome (the preserved speech variant)

The preserved speech variant is the milder form of Rett syndrome: affected girls show the same stages of this condition and by the second half of the first decade are making slow progress in manual and verbal abilities. They walk without help, and may be able to make simple drawings and write a few words. Most of them can speak in sentences. Autistic behavior can often be observed. We previously described several cases in the pre-molecular era and subsequently reported a survey of 12 cases with MECP2 mutations. Seventeen new patients with the preserved speech variant and a proven MECP2 mutation have been clinically evaluated. Additional clinical data of our previously described cases are reported. These 29 preserved speech variant cases were compared with 129 classic Rett patients using a clinical severity score system including 22 different signs. There was both statistical and clinical evidence of the existence of this variant. On the basis of their abilities these girls can be distinguished as low-, intermediate- and high-functioning. Girls of the last two groups show a greater homogeneity: they speak in sentences, use their hands more easily, have normal somatic features, mild neurovegetative abnormalities, with autistic behavior in 76%, epilepsy in 30%, while girls of the first group are closer to classic Rett syndrome. The majority of patients carries either missense mutations (especially the p.R133C change) or late truncating mutations in the MECP2 gene. These results confirm the existence of this variant of Rett syndrome (Zappella variant), a clear example of progress of manual and verbal abilities, and not of a "preserved speech" and suggest corresponding diagnostic criteria.

Three Rett patients with both MECP2 mutation and 15q11-13 rearrangements

Autism and Rett syndrome, a severe neurological disorder with autistic behavior, are classified as separate disorders on clinical and etiological ground. Rett syndrome is a monogenic X-linked dominant condition due to de novo mutations in the MECP2 gene, whereas autism is a neurodevelopmental and behavioral disorder with complex genetic basis. Maternally inherited duplications on 15q11-q13 are found in a fraction of autistic children suggesting that an abnormal dosage of gene(s) within this region might cause susceptibility to autism. Now we show that three Rett patients are carriers of both a MECP2 mutation and a 15q11-q13 rearrangement, suggesting that there might be a relationship between autism-related genes and the MECP2 gene.

MECP2 and beyond: phenotype-genotype correlations in Rett syndrome

The association of Rett syndrome with pathogenic mutations of the methyl-CpG binding protein 2 (MECP2) gene was first made in 1999. Since that time, it has been found that the clinical phenotype can, at least in part, be explained in terms of the type and location of the MECP2 mutation and epigenetic factors such as skewing of X-chromosome inactivation. In addition, MECP2 mutations may be associated with non-Rett syndrome clinical phenotypes, including nonsyndromic and syndromic X-linked mental retardation and Angelman-like phenotypes. Intense research efforts are currently focused on understanding the pathogenesis of Rett syndrome, using sophisticated techniques such as microarray analysis, and the development of mouse models, with an ultimate aim being the development of targeted therapies that could ameliorate or even prevent the devastating consequences of this enigmatic neurodevelopmental disorder.

Rett syndrome: the complex nature of a monogenic disease

Rett syndrome (RTT) is a severe neurodevelopmental disorder affecting almost exclusively girls. It is currently considered a monogenic X-linked dominant disorder due to mutations in MECP2 gene, encoding the methyl-CpG binding protein 2. A few RTT male cases, resulting from mosaicism for MECP2 mutations, have been reported. Male germline MECP2 mutations cause either severe encephalopathy with death at birth (usually in brothers of classical RTT females) or X-linked recessive mental retardation (XLMR). To date the wide phenotypic heterogeneity associated with MECP2 mutations in females (from classical RTT to healthy carriers) has been explained by differences in X chromosome inactivation. However, conflicting results have been obtained in different studies, with both random and highly skewed X-inactivation reported in healthy carrier females. Consequently it is possible that mechanisms other than X-inactivation play a role in the expressivity of MECP2 mutations. To explain the phenotypic heterogeneity associated with MECP2 mutations we propose a digenic model in which the presence of a "mutated" allele in a second gene, leading to a less functional protein, determines the clinical severity of the MECP2 mutation. The model is supported by the identification of the same mutation in XLMR and RTT cases. The carrier mothers of XLMR families are clinically asymptomatic and present balanced X chromosome inactivation. Therefore the same mutation arising in different genetic backgrounds can cause XLMR in males, remain silent in the carrier females and cause classic RTT in females. MECP2 mutations account for approximately 70-80% of classic RTT cases. MECP2 negative cases might result from mutations in noncoding regions of MECP2 gene. Alternatively, these cases might be due to mutations in other genes (locus heterogeneity). This hypothesis is supported by the identification of several chromosomal rearrangements in MECP2 negative patients with RTT and RTT-like phenotypes. MeCP2 is considered a general transcriptional repressor. However, conditional mouse mutants with selective loss of Mecp2 in the brain develop clinical manifestations similar to RTT, indicating that MECP2 is exclusively required for central nervous system function. The involvement of MeCP2 in methylation-specific transcriptional repression suggests that MECP2 related disorders result from dysregulated gene expression. Studies on gene expression have been performed in mouse and human brains. A relatively small number of gene expression changes were identified. It is possible that MeCP2 causes dysregulation of a very small subset of genes that are not detected with this method of analysis, or that very subtle changes in many genes cause the neuronal phenotype.

Effects of MECP2 mutation type, location and X-inactivation in modulating Rett syndrome phenotype

Rett syndrome (RTT) is a clinically defined disorder that describes a subset of patients with mutations in the X-linked MECP2 gene. However, there is a high degree of variability in the clinical phenotypes produced by mutations in MECP2, even amongst classical RTT patients. In a large-scale screening project, this variability has been examined by looking at the effects of mutation type, functional domain affected and X-inactivation. Mutations have been identified in 60% of RTT patients in this study (25% of whom were atypical), including 23 novel mutations and polymorphisms. More mutations were found in classical patients (63%) compared to atypical patients (44%). All of the pathogenic mutations were de novo in patients for whom parent DNA was available for screening. A composite phenotype score was developed, based on the recommendations for reporting clinical features in RTT of an international collaborative group. This score proved useful for summarising phenotypic severity, but did not correlate with mutation type, domain affected or X-inactivation, probably due to complex interactions between all three. Other correlations suggested that truncating mutations and mutations affecting the methyl-CpG-binding domain tend to lead to a more severe phenotype. Skewed X-inactivation was found in a large proportion (43%) of our patients, particularly in those with truncating mutations and mutations affecting the MBD. It is therefore likely that X-inactivation does modulate the phenotype in RTT.

Mind and brain in Rett disorder

Development and retention of speech is reported in 265 people with Rett syndrome: 30% (80) never gained real words, 55% (145) gained real words and lost them, 15%(40) retained some words and 6% of the total (16/265) continued to use phrases appropriately. Morphological studies of the cytoarchitecture of the speech areas in 14 cases indicate the existence of interhemispheric differences which form part of the infrastructure for speech processing. Ten adults with Rett syndrome and with meaningful speech are compared to age matched adults without speech. The profile of mind and strategies for coping with its problems are described by a family. Although the range in severity is wide the mental profile is remarkably consistent across the severity range with regard to both positive and negative aspects.

Preserved speech variants of the Rett syndrome: molecular and clinical analysis

Mutations in the MECP2 gene cause the severe neurodevelopmental disorder called Rett syndrome. Preliminary evidence suggests that MECP2 may be involved in a broader phenotype than classical Rett syndrome including preserved speech variants (PSV). Here we report clinical and mutation analysis of 18 PSV patients. Ten of them had a MECP2 mutation (55%). The clinical features of these girls have been characterized and two subgroups defined. All of them had slow recovery of verbal and praxic abilities, evident autistic behavior, and normal head circumference. Six were overweight, often obese, had kyphosis, coarse face, and mental age of two-to-three years, and were able to speak in sentences; four had normal weight, mental age not beyond one-to-two years, and spoke in single words and two-word phrases. The course of the disorder was in stages as in classic Rett syndrome. Hand-washing was present in the first years of life but often subsequently disappeared. Significantly, all mutations found in PSV are either missense or late truncating mutations. In particular, we did not find the four early truncating hot spots: R168X, R255X, R270X, R294X. These results suggest that early truncating mutations lead to a poor prognosis (classic Rett), while late truncating and missense mutations lead either to classic Rett or PSV. We hypothesize that a missense or late truncating mutation is necessary but not sufficient to produce a PSV, based on the presence of one (or more) modifier genes whose product may interact in a epistatic manner with MeCP2 protein.

The preserved speech variant: a subgroup of the Rett complex: a clinical report of 30 cases

Thirty girls and young women, 6 from Sweden and 24 from Italy, are described in this paper. They ranged in age from 5 through 28 years. All but one of the cases met full symptom criteria for DSM-IV autistic disorder. However, they also showed many features of classic Rett syndrome (RS) as outlined by the Rett syndrome Diagnostic Criteria Work Group. All met the required 3 out of 6 main criteria and 47% also met both these and the required 5 out of 11 supportive criteria for RS variants as outlined by Hagberg. The course of the disorder was more benign than in classic RS, but all the girls were severely functionally impaired. There was familial clustering in a subgroup. It is concluded that these 30 cases represent a syndrome, similar and probably related, to classic RS. It is suggested that there is a spectrum of syndromes ranging from severe cases with classical presentation to considerably milder variants. We propose that, at the present state of knowledge, these conditions might be best categorized as subgroups of the "Rett Complex," in which classical RS and the preserved speech variant may be the most frequent.