Eric Smeets

MLL2 mutation spectrum in 45 patients with Kabuki syndrome

Kabuki Syndrome (KS) is a rare syndrome characterized by intellectual disability and multiple congenital abnormalities, in particular a distinct dysmorphic facial appearance. KS is caused by mutations in the MLL2 gene, encoding an H3K4 histone methyl transferase which acts as an epigenetic transcriptional activator during growth and development. Direct sequencing of all 54 exons of the MLL2 gene in 45 clinically well‐defined KS patients identified 34 (75.6%) different mutations. One mutation has been described previously, all others are novel. Clinically, all KS patients were sporadic, and mutations were de novo for all 27 families for which both parents were available. We detected nonsense (n=11), frameshift (n=17), splice site (n=4) and missense (n=2) mutations, predicting a high frequency of absent or non‐functional MLL2 protein. Interestingly, both missense mutations located in the C‐terminal conserved functional domains of the protein. Phenotypically our study indicated a statistically significant difference in the presence of a distinct facial appearance (p=0.0143) and growth retardation (p=0.0040) when comparing KS patients with an MLL2 mutation compared to patients without a mutation. Our data double the number of MLL2 mutations in KS reported so far and widen the spectrum of MLL2 mutations and disease mechanisms in KS.

Neurodevelopmental disorders in males related to the gene causing Rett syndrome in females (MECP2)

Mutations in the MECP2 (methyl-CpG-binding protein 2) gene are known to cause Rett syndrome, a well-known and clinically defined neurodevelopmental disorder. Rett syndrome occurs almost exclusively in females and for a long time was thought to be an X-linked dominant condition lethal in hemizygous males. Since the discovery of the MECP2 gene as the cause of Rett syndrome in 1999, MECP2 mutations have, however, also been reported in males. These males phenotypically have classical Rett syndrome when the mutation arises as somatic mosaicism or when they have an extra X chromosome. In all other cases, males with MECP2 mutations show diverse phenotypes different from classical Rett syndrome. The spectrum ranges from severe congenital encephalopathy, mental retardation with various neurological symptoms, occasionally in association with psychiatric illness, to mild mental retardation only. We present a 21-year-old male with severe mental retardation, spastic tetraplegia, dystonia, apraxia and neurogenic scoliosis. A history of early hypotonia evolving into severe spasticity, slowing of head growth, breathing irregularities and good visual interactive behaviour were highly suggestive of Rett syndrome. He has a de novo missense mutation in exon 3 of the MECP2 gene (P225L). The clinical spectrum and molecular findings in males with MECP2 mutations are reviewed.

Rett syndrome in females with CTS hot spot deletions: a disorder profile.

From a series of 107 females with Rett syndrome (RTT), we describe the long‐term history of ten females with a deletion in the C‐terminus of the MECP2 gene. We observed that their disorder profile is clinically recognizable with time and different from other atypical and milder RTT phenotypes. In females with hot spot deletions in the C‐terminus, dystonia is present from childhood and results in a serious spine deformation in spite of preventive measures. Their adaptive behavior is surprisingly better preserved and in contrast with the typical decline in motor functioning. The delineaton of disorder profiles by long‐term clinical observation can teach us about genotype/phenotype relationships and eventually about the effect of epigenetic phenomena on the final phenotype.

Mutations in DDX3X Are a Common Cause of Unexplained Intellectual Disability with Gender-Specific Effects on Wnt Signaling

Intellectual disability (ID) affects approximately 1%-3% of humans with a gender bias toward males. Previous studies have identified mutations in more than 100 genes on the X chromosome in males with ID, but there is less evidence for de novo mutations on the X chromosome causing ID in females. In this study we present 35 unique deleterious de novo mutations in DDX3X identified by whole exome sequencing in 38 females with ID and various other features including hypotonia, movement disorders, behavior problems, corpus callosum hypoplasia, and epilepsy. Based on our findings, mutations in DDX3X are one of the more common causes of ID, accounting for 1%-3% of unexplained ID in females. Although no de novo DDX3X mutations were identified in males, we present three families with segregating missense mutations in DDX3X, suggestive of an X-linked recessive inheritance pattern. In these families, all males with the DDX3X variant had ID, whereas carrier females were unaffected. To explore the pathogenic mechanisms accounting for the differences in disease transmission and phenotype between affected females and affected males with DDX3X missense variants, we used canonical Wnt defects in zebrafish as a surrogate measure of DDX3X function in vivo. We demonstrate a consistent loss-of-function effect of all tested de novo mutations on the Wnt pathway, and we further show a differential effect by gender. The differential activity possibly reflects a dose-dependent effect of DDX3X expression in the context of functional mosaic females versus one-copy males, which reflects the complex biological nature of DDX3X mutations.

Melkersson-Rosenthal syndrome and de novo autosomal t(9;21)(p11;p11) translocation.

In this report we describe a 26‐year‐old female with the typical clinical symptoms and signs of Melkersson‐Rosenthal syndrome, an autosomal dominant disorder with variable expression, and a de novo t(9;21)(p11;p11), and suggest that the “Melkersson‐Rosenthal gene” is located at 9p11.

Cardiorespiratory challenges in Rett's syndrome

www.thelancet.com Vol 371 June 14, 2008 1981 Rett’s syndrome is a genetic neurodevelopmental disorder with brainstem immaturity that aff ects one in 10 000 women. The condition shows the importance of the brainstem in cardiorespiratory medicine. There is a lack of understanding of the cardiorespiratory disturbance in the disorder within the medical community, which makes management a challenge. Therefore an international group of experienced medical practitioners from various disciplines gathered in the Swedish National Rett Centre, Frösön, to collate their experience on Rett’s syndrome and provide a practical management strategy for all health-care tiers: the Frösö Declaration. The six cardinal features of Rett’s syndrome (table) are age-dependent. Abnormalities become evident during the fi rst or second year of life. A regression stage, characterised by an exacerbation of brainstem features, usually seems to take place in the second year. There is poor parasympathetic development, leading to a unique sympathovagal imbalance with the misleading impression of sympathetic overactivity. A lack of integrative inhibitions in the brainstem pre vents appropriate cardiovascular regulation during abnor mal breathing, causing an increased risk of adverse cardiorespiratory events. Brainstem disorders are the main reasons to seek urgent medical atten tion in Rett’s syndrome throughout life. Multiorgan involvement of in breathing-related metabolic disorders needs professional care and includes cardiologists, anaesthetists, respiratory physicians, endocrinologists, nutritionists, neurologists, paediatricians, and general practitioners. Early diagnosis to avoid long-term medical uncertainty is the primary aim. A search for mutations in the MECP2 gene in infants with unexplained developmental slurring is recommended. Then the cardiorespiratory phenotype should be established at the onset of brainstem disorders, because each of the three phenotypes is unique and needs a specifi cally tailored management strategy. Establishing the cardiorespiratory phenotype requires detailed neurophysiology. The primary pathophysiology is a defective control mechanism of carbon dioxide exhalation that leads to respiratory alkalosis or acidosis. Patients with phenotype 1 are forceful breathers who usually have fi xed low concentrations of partial pressure of carbon dixoide (pCO2), causing chronic respiratory alka losis. To interrupt an episode of forceful breathing, we recom mend fi rst re-breathing into a 5-L bag attached Cardiorespiratory challenges in Rett’s syndrome two-thirds of Tibetan people have not had access to iodised salt. Despite the overall poor coverage, the picture is not all bleak. In Tibet, there are 890 primary schools, 118 middle schools, and 1568 teaching. Of the 470 000 students attending these schools, three-quarters eat in school dining halls 5 days a week. Happily, all school dining halls in Tibet use iodised salt in accordance with a policy and schools health-promotion programme set out by the Education Bureau of Tibet in 2005. Since then, around 350 000 school children consume iodised salt at least 5 days a week, thus achieving the required intake of iodine for children.

Rett syndrome in adolescent and adult females: Clinical and molecular genetic findings

Rett syndrome (RTT) is a neurodevelopmental disorder which is diagnosed clinically. We report on 30 adolescent and adult females with classical or atypical RTT of whom 24 have a MECP2 mutation. In these 24 females, the clinical manifestations, degree of severity, and disorder profiles are discussed as well as the genotype phenotype correlation. After X‐chromosome inactivation (XCI) study in these cases, we found no correlation between skewing and milder phenotype. Three large deletions were found after additional Southern blot analysis in three classical RTT cases. We confirm that early truncating mutations in MECP2 are responsible for a more severe course of the disorder. Three disorder profiles related to the missense mutations R133C and R306C, and to deletions in the C terminal segment are described and are of interest for further clinical study on larger numbers of cases. The R133C genotype has a predominantly autistic presentation while the R306C genotype is associated with a slower disease progression. The phenotype of the “hotspot” deletions in the C terminal segment is predominantly characterized by rapid progressive neurogenic scoliosis. Older women with RTT are underdiagnosed: seven adults were first diagnosed as having RTT between 29 and 60 years of age, and confirmed on finding a MECP2 mutation. Knowledge of the clinical phenotype of RTT at an adult age is important for all involved in the care of these individuals. The involvement of the parent support group is very important in this matter.

Communication in Individuals with Rett Syndrome: an Assessment of Forms and Functions

In the present study we assessed the forms and functions of prelinguistic communicative behaviors for 120 children and adults with Rett syndrome using the Inventory of Potential Communicative Acts (IPCA) (Sigafoos et al. Communication Disorders Quarterly 21:77–86, 2000a). Informants completed the IPCA and the results were analysed to provide a systematic inventory and objective description of the communicative forms and functions present in each individual’s repertoire. Results show that respondents reported a wide variety of communicative forms and functions. By far most girls used prelinguistic communicative behaviors of which eye contact/gazing was the most common form. The most often endorsed communicative functions were social convention, commenting, answering, requesting and choice-making. Problematic topographies (e.g., self-injury, screaming, non-compliance) were being used for communicative purposes in 10 to 41% of the sample. Exploratory analyses revealed that several communicative forms and functions were related to living environment, presence/absence of epilepsy, and age. That is, higher percentages of girls who showed some forms/functions were found in those who lived at home, who had no epilepsy and who were relatively young.

Tumor spectrum in children with Noonan syndrome and SOS1 or RAF1 mutations

Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11‐ and KRAS‐negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1‐positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations.

MYT1L is a candidate gene for intellectual disability in patients with 2p25.3 (2pter) deletions.

A partial deletion of chromosome band 2p25.3 (2pter) is a rarely described cytogenetic aberration in patients with intellectual disability (ID). Using microarrays we identified deletions of 2p25.3, sized 0.37–3.13 Mb, in three adult siblings and three unrelated patients. All patients had ID, obesity or overweight and/or a square‐shaped stature without overt facial dysmorphic features. Combining our data with phenotypic and genotypic data of three patients from the literature we defined the minimal region of overlap which contained one gene, i.e., MYT1L. MYT1L is highly transcribed in the mouse embryonic brain where its expression is restricted to postmitotic differentiating neurons. In mouse‐induced pluripotent stem cell (iPS) models, MYT1L is essential for inducing functional mature neurons. These resemble excitatory cortical neurons of the forebrain, suggesting a role for MYT1L in development of cognitive functions. Furthermore, MYT1L can directly convert human fibroblasts into functional neurons in conjunction with other transcription factors. MYT1L duplication was previously reported in schizophrenia, indicating that the gene is dosage‐sensitive and that shared neurodevelopmental pathways may be affected in ID and schizophrenia. Finally, deletion of MYT1, another member of the Myelin Transcription Factor family involved in neurogenesis and highly similar to MYT1L, was recently described in ID as well. The identification of MYT1L as candidate gene for ID justifies further molecular studies aimed at detecting mutations and for mechanistic studies on its role in neuron development and on neuropathogenic effects of haploinsufficiency.