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.

This multicenter investigation into the phenotypic correlates of MECP2 mutations in Rett syndrome has provided a greater depth of understanding than hitherto available about the specific phenotypic characteristics associated with commonly occurring mutations. Although the modifying influence of X inactivation on clinical severity could not be included in the analysis, the findings confirm clear genotype-phenotype relationships in Rett syndrome and show the benefits of collaboration crucial to effective research in rare disorders.

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Mutations in the methyl-CpG-binding protein gene MECP2 at Xq28 cause Rett syndrome (RTT), an X-linked dominant neurodevelopmental disorder characterized by a period of stagnation followed by regression in the development of young girls. Mutations were sought in MECP2 in 48 females with classical sporadic RTT, seven families with possible familial RTT and five sporadic females with features suggestive, but not diagnostic of RTT. Long distance PCR coupled with long-read direct sequencing was employed to sequence the entire MECP2 gene coding region in all cases. Mutations were identified in 44/55 (80%) unrelated classical sporadic and familial RTT patients, but only 1/5 (20%) sporadic cases with suggestive but non-diagnostic features of RTT. Twenty-one different mutations were identified (12 missense, four nonsense and five frame-shift mutations); 14 of these were novel. All missense mutations were located either in the methyl-CpG-binding domain or in the transcription repression domain. Nine recurrent mutations were characterized in a total of 33 unrelated cases (73% of all cases with MECP2 mutations). Significantly milder disease was noted in patients carrying missense mutations as compared with those with truncating mutations ( P = 0. 0023), and milder disease was associated with late as compared with early truncating mutations ( P = 0.0190).

BackgroundChildren and families living with rare disease often experience significant health, psychosocial, economic burdens and diagnostic delays. Experiences appear to be constant, regardless of the specific rare disease diagnosis. Systematically collected Australian data to support policy response on rare diseases are scarce. We address this gap by providing survey results about 462 children aged <19 years living with approximately 200 different rare diseases.ResultsOf 462 children, 96% were born in Australia, 55% were male, median age was 8.9 years (0–18.2). Four-hundred-and-twenty-eight (93%) had received a definitive diagnosis but 29 (7%) remained undiagnosed. Before receiving the correct diagnosis 38% consulted ≥ 6 different doctors. Among those with a diagnosis, 37% believed the diagnosis was delayed and 27% initially received a wrong diagnosis. Consequences of delayed diagnosis include anxiety, loss of reproductive confidence because of an ill-defined genetic risk, frustration and stress (54%), disease progression (37%), delays in treatment (25%) and inappropriate treatments (10%). Perceived reasons for diagnostic delays included lack of knowledge about the disease among health professionals (69.2%), lack of symptom awareness by the family (21.2%) and difficulties accessing tests (17.9%). Children with inborn errors of metabolism were less likely to have a delayed diagnosis compared with other disease groups (Chi-Sq = 17.1; P < 0.0001), most likely due to well-established and accessible biochemical screening processes. Diagnosis was given in person in 74% of cases, telephone in 18.5% and via a letter in 3.5%. Some families (16%) were dissatisfied with the way the diagnosis was delivered, citing lack of empathy and lack of information from health professionals. Psychological support at diagnosis was provided to 47.5%, but 86.2% believed that it should always be provided. Although 74.9% of parents believed that the diagnosis could have an impact on future family planning, only 44.8% received genetic counselling.ConclusionParents of children living with rare chronic and complex diseases have called for better education, resourcing of health professionals to prevent avoidable diagnostic delays, and to facilitate access to early interventions and treatments. Access to psychological support and genetic counselling should be available to all parents receiving a life-changing diagnosis for their child.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-017-0622-4) contains supplementary material, which is available to authorized users.

Advancing paternal and maternal age have both been associated with risk for autism spectrum disorders (ASD). However, the shape of the association remains unclear, and results on the joint associations is lacking. This study tests if advancing paternal and maternal ages are independently associated with ASD risk and estimates the functional form of the associations. In a population-based cohort study from five countries (Denmark, Israel, Norway, Sweden and Western Australia) comprising 5 766 794 children born 1985–2004 and followed up to the end of 2004–2009, the relative risk (RR) of ASD was estimated by using logistic regression and splines. Our analyses included 30 902 cases of ASD. Advancing paternal and maternal age were each associated with increased RR of ASD after adjusting for confounding and the other parent's age (mothers 40–49 years vs 20–29 years, RR=1.15 (95% confidence interval (CI): 1.06–1.24), P-value<0.001; fathers⩾50 years vs 20–29 years, RR=1.66 (95% CI: 1.49–1.85), P-value<0.001). Younger maternal age was also associated with increased risk for ASD (mothers <20 years vs 20–29 years, RR=1.18 (95% CI: 1.08–1.29), P-value<0.001). There was a joint effect of maternal and paternal age with increasing risk of ASD for couples with increasing differences in parental ages. We did not find any support for a modifying effect by the sex of the offspring. In conclusion, as shown in multiple geographic regions, increases in ASD was not only limited to advancing paternal or maternal age alone but also to differences parental age including younger or older similarly aged parents as well as disparately aged parents.

It is fifty years since Andreas Rett first described Rett syndrome, a disorder now known to be caused by a mutation in the MECP2 gene. A compelling blend of astute clinical observations, clinical and laboratory research has already built our understanding of Rett syndrome and its biological underpinnings. We document the contributions of the early pioneers and describe the evolution of knowledge in terms of diagnostic criteria, clinical variation and the interplay with other Rett-related disorders. We provide a synthesis of what is known about the neurobiology of MeCP2, the lessons from both cell and animal models and how they may inform future clinical trials. With a focus on the core criteria, we examine the relationships that have been demonstrated between genotype and clinical severity. We review what is known about the many comorbidities that occur in this disorder and how genotype may also modify their presentation. We acknowledge the important drivers that are accelerating this research program including the roles of research infrastructure, international collaboration and advocacy groups. Finally, we conclude by highlighting the major milestones since 1966 and what they mean for the day-to-day lives of those with Rett syndrome and their families. Key pointsThere has been an explosion of knowledge about Rett syndrome in relation to its genetic basis, clinical characteristics and their relationships during the fifty years since the disorder was first described by Andreas Rett.Whilst initially the diagnosis of Rett syndrome was based only on clinical criteria, identifying its genetic cause has had a major positive impact on how clinicians diagnose the disorder but also provides new challenges as we enter the era of next generation sequencing.

BackgroundAs well as being highly comorbid conditions, autism spectrum disorders (ASD) and intellectual disability (ID) share a number of clinically-relevant phenomena. This raises questions about similarities and overlap in diagnosis and aetiological pathways that may exist for both conditions.AimsTo examine maternal conditions and perinatal factors for children diagnosed with an ASD, with or without ID, and children with ID of unknown cause, compared with unaffected children.MethodsThe study population comprised all live singleton births in Western Australia (WA) between January 1984 and December 1999 (N = 383,153). Univariate and multivariate multinomial logistic regression models were applied using a blocked modelling approach to assess the effect of maternal conditions, sociodemographic factors, labour and delivery characteristics and neonatal outcomes.ResultsIn univariate analyses mild-moderate ID was associated with pregnancy hypertension, asthma, urinary tract infection, some types of ante-partum haemorrhage, any type of preterm birth, elective C-sections, breech presentation, poor fetal growth and need for resuscitation at birth, with all factors showing an increased risk. Severe ID was positively associated with poor fetal growth and need for resuscitation, as well as any labour or delivery complication. In the multivariate analysis no maternal conditions or perinatal factors were associated with an increased risk of ASD without ID. However, pregnancy hypertension and small head circumference were associated with a reduced risk (OR = 0.64, 95% CI: 0.43, 0.94; OR = 0.58, 95% CI: 0.34, 0.96, respectively). For ASD with ID, threatened abortion before 20 weeks gestation and poor fetal growth were associated with an increased risk.ConclusionFindings show that indicators of a poor intrauterine environment are associated with an elevated risk of ID, while for ASD, and particularly ASD without ID, the associations are much weaker. As such, these findings highlight the importance of accounting for the absence or presence of ID when examining ASD, if we are to improve our understanding of the causal pathways associated with these conditions.