Classical Rett syndrome in sisters: variability of clinical expression

Monozygotic twins with Rett syndrome: Phenotyping the first two years of life

The first two years of life for children with Rett syndrome (RTT) have previously been viewed as relatively asymptomatic. However, it is possible that subtle symptoms may be present in early development. To identify possible early indicators of RTT, we analysed videotapes of two twin girls with RTT. The videotapes were analysed to (a) describe the motor and communicative development of this twin pair with RTT; and to (b) explore whether early abnormalities and their age of onset differed between the twins and were related to their later clinical phenotypes. The results indicated several neurodevelopmental abnormalities present before the children exhibited any obvious signs of regression. Abnormalities were evident in the motor, speech-language and communicative domains. These data support an emerging evidence base showing the presence of developmental abnormalities in children with RTT during the first year of life. The results have implications for early screening and clinical assessment.

Distinct de novo deletions in a brother-sister pair with RTT: a case report

Rett syndrome (RTT), a neurodevelopmental disorder caused by mutations in the X-linked gene encoding methyl-CpG-binding protein2 (MeCP2), is a leading cause of mental retardation in females. Majority of cases are sporadic (99%) but some familial cases have also been observed. We describe a familial study with a brother-sister pair with symptoms of RTT and exhibiting distinct deletions in the MECP2. The non-shared de novo deletion in the two sibs provides important insights into the disease etiology, especially for male sibs showing varied phenotypes as compared to the classical ones seen in the females.

Mutations of CDKL5 cause a severe neurodevelopmental disorder with infantile spasms and mental retardation

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused, in most classic cases, by mutations in the X-linked methyl-CpG-binding protein 2 gene (MECP2). A large degree of phenotypic variation has been observed in patients with RTT, both those with and without MECP2 mutations. We describe a family consisting of a proband with a phenotype that showed considerable overlap with that of RTT, her identical twin sister with autistic disorder and mild-to-moderate intellectual disability, and a brother with profound intellectual disability and seizures. No pathogenic MECP2 mutations were found in this family, and the Xq28 region that contains the MECP2 gene was not shared by the affected siblings. Three other candidate regions were identified by microsatellite mapping, including 10.3 Mb at Xp22.31-pter between Xpter and DXS1135, 19.7 Mb at Xp22.12-p22.11 between DXS1135 and DXS1214, and 16.4 Mb at Xq21.33 between DXS1196 and DXS1191. The ARX and CDKL5 genes, both of which are located within the Xp22 region, were sequenced in the affected family members, and a deletion of nucleotide 183 of the coding sequence (c.183delT) was identified in CDKL5 in the affected family members. In a screen of 44 RTT cases, a single splice-site mutation, IVS13-1G-->A, was identified in a girl with a severe phenotype overlapping RTT. In the mouse brain, Cdkl5 expression overlaps--but is not identical to--that of Mecp2, and its expression is unaffected by the loss of Mecp2. These findings confirm CDKL5 as another locus associated with epilepsy and X-linked mental retardation. These results also suggest that mutations in CDKL5 can lead to a clinical phenotype that overlaps RTT. However, it remains to be determined whether CDKL5 mutations are more prevalent in specific clinical subgroups of RTT or in other clinical presentations.

The role of different X-inactivation pattern on the variable clinical phenotype with Rett syndrome

A gene for Methyl-CpG binding protein 2 (MECP2), which locates Xq28, was recently found to be responsible for Rett syndrome. Although mutational analyses of MECP2 in Rett syndrome have been extensively analyzed, the mechanism(s) by which variable clinical phenotype occurred between affected monozygotic twins or sisters have not been clarified. We hypothesized that the difference of X-inactivation pattern might explain this phenomenon. With the method based on methylation-specific PCR, we analyzed polymorphic trinucleotide repeat in the human andorogen receptor gene mapped on Xq11.2-12, using DNA samples derived from previously described monozygotic twins and sisters together with their parents. Their clinical phenotypes were reported to be significantly different between siblings. We found that (1) maternally derived allele is predominantly active than paternally derived one in three out of four patients analyzed, (2) remaining one twin patient, whose ratio of active paternal allele is almost the same level as maternal allele, showed far much severe phenotype when compared with her counterpart. Together with the finding that most of the alleles with de novo mutation are from paternal X chromosome in sporadic cases, the existence of a mechanism that suppresses mutated paternal allele activation, resulting skewed X-inactivation to make clinical phenotype milder, might be speculated. Thus, when this mechanism fails to work sufficiently by an unknown reason, severer clinical phenotype could occur.

Reduced nerve growth factor in Rett syndrome postmortem brain tissue

To determine whether reduced nerve growth factor (NGF) and/or its high affinity receptor, trkA, play a role in the pathophysiology of Rett syndrome (RS), we used immunohistochemistry in paraffin-embedded human autopsy brain tissue, to quantify NGF and trkA levels within the frontal cortex of 9 RS females and 10 female controls of similar age. The results showed a significant reduction of NGF expression in RS patients (p < 0.001). Specifically, all RS brains exhibited NGF levels at or below the minimum level observed in controls. In 3 RS brains there was no NGF detected. TrkA expression was also reduced in the RS group (p = 0.035). Interestingly, the expression of NGF in the RS group was significantly related to the presence of cortical astrogliosis (r = 0.91) as indicated by immunostaining for glial fibrillary acidic protein (GFAP). This suggests that while the signals for NGF production during injury remain intact, the critical developmental signals required for early NGF production are impaired.

Serum melatonin kinetics and long-term melatonin treatment for sleep disorders in Rett syndrome

We studied the circadian rhythm of serum melatonin levels in two patients with classical Rett syndrome having severe sleep disorders; serum melatonin levels were measured before and during melatonin treatment using radioimmunoassay. Patient 1 had a free-running rhythm of sleep-wake cycle from 3 years of age. At the age of 4 years, the peak time of melatonin was delayed 6 h compared to normal control and the peak value was at the lower limit. Patient 2 had a fragmented sleep pattern accompanied by night screaming from 1 year and 6 months of age. At the age of 10 years, the peak time of melatonin secretion was normal but the peak value was at the lower limit. These patients were given 5 mg melatonin orally prior to bedtime. Exogenous melatonin dramatically improved the sleep-wake cycle in patient 1. In patient 2, exogenous melatonin showed a hypnotic effect but early morning awakenings occurred occasionally. When melatonin treatment was stopped, the sleep disorders recurred and re-administration of 3 mg melatonin was effective in both patients. The effect was maintained over 2 years without any adverse effects. These findings suggests that sleep disorders in patients with Rett syndrome may relate with an impaired secretion of melatonin.