Borivoj Petrak

Homozygous EXOSC3 Mutation c.92G→C, p.G31A is a Founder Mutation Causing Severe Pontocerebellar Hypoplasia Type 1 Among the Czech Roma

Abstract Pontocerebellar hypoplasia type 1 (PCH1) is characterized by cerebellar and anterior horn motor neuron degeneration and loss, signs of spinal muscular atrophy plus. Patients manifest severe perinatal weakness, hypotonia, and respiratory insufficiency, causing death frequently before the age of 1 year. Recently, causative mutations in EXOSC3 were reported in a majority of PCH1 patients, but the detailed clinical phenotype caused by EXOSC3 mutations, genotype-phenotype correlations, and prevalent mutations in specific ethnic groups is not yet known. Three unrelated Czech Roma patients with PCH1 were investigated clinically, electrophysiologically, neuroradiologically, and neuropathologically (patients 1 and 2). The entire coding region of the EXOSC3 gene, including the adjacent intron sequences, was sequenced in all three patients. The same mutation c.92G→C, p.G31A in EXOSC3 was found in all three affected patients in homozygous state and in heterozygous state in the parents from two of the families. Haplotype analysis with four flanking microsatellite markers showed identical haplotype in 9 out of 11 haplotypes carrying the c.92G→C, p.G31A mutation. Furthermore, four heterozygotes for this mutation were found in anonymous DNA samples from 90 unrelated Roma individuals. All four of these samples shared the same haplotype. No heterozygous sample was found among 120 anonymous DNA samples from Czech non-Roma individuals with no familial relation. It may therefore be concluded that EXOSC3 c.92G→C, p.G31A mutation is a founder mutation with high prevalence among the Czech Roma causing a similar and particularly severe phenotype of PCH1. These observations from the Czech Roma may have consequences also for other Roma from other countries. PCH1 caused by EXOSC3 founder mutation c.92G→C, p.G31A extends the list of autosomal recessive disorders rare among the general population but more frequent among Roma at least in the Czech Republic.

A girl with neurofibromatosis type 1, atypical autism and mosaic ring chromosome 17

We describe a girl with neurofibromatosis type 1 (NF1), mild dysmorphic features, growth and mental retardation, autism, and mosaicism of ring chromosome 17 and chromosome 17 monosomy. The extent of genetic material deleted from the ring chromosome was determined using a combination of classical cytogenetics, fluorescence in situ hybridization (FISH) and multiplex ligation‐dependent probe amplification (MLPA) to be 0.6–2.5 Mb on 17p, and up to about 10 Mb on 17q. Based on our observations and on a review of the literature we argue that in addition to a universal “ring syndrome” which is based on ring instability and is less specific for the chromosome involved, various ring chromosomes underlie their own characteristic phenotypes. We propose that the symptoms leading to the diagnosis of NF1 in our patient could be attributed to mosaic hemizygosity for the NF1 gene in some of her somatic cells. A similar mechanism or a direct involvement of respective disease genes in the aberration could possibly influence also the development of autism and other symptoms. We raise a question if the loss of one copy of chromosome 17 from a substantial fraction of somatic cells can have specific consequences also for future risks of the patient, for example, due to the mosaic hemizygosity for the BRCA1 and TP53 genes.

The importance of advanced parental age in the origin of neurofibromatosis type 1.

Von Recklinghausen neurofibromatosis (NF1) is an autosomal dominant disorder with a prevalence about 1/3,000 (1/2,000–1/5,000 in various population‐based studies). About 30–50% of cases are sporadic, resulting from a new mutation. NF1 is fully penetrant by mid‐childhood, stigmata, and medical problems (neurological, dermatological, endocrine, ophthalmological, oncological) are highly variable. Advanced paternal age (APA) has been known to increase the risk of new germline mutations that contribute to the presence of a variety of genetic diseases in the human population. The trend in developed countries has been toward higher parental age due to various reasons. In a cross‐sectional study, in two university hospital centers, data on parental age of 103 children (41 female) born between 1976 and 2005 with sporadic NF1 were analyzed. Parental age at birth was compared with the Czech general population matched to birth year. The mean NF1 sporadic case paternal age at birth was 32.0 years (95% CI 30.7–33.3 years) compared with 28.8 years (95% CI 28.6–29.1 years) in the general population (P < 0.001). The mean maternal age at birth was 27.4 years (95% CI 26.3–28.5 years) compared with 25.8 years (95% CI 25.5–26.0 years) in the general population (P < 0.05). The case‐control difference in the fathers age was higher than it was for the mothers age. Sporadic NF1 cases accounted for 35.6% of our entire NF1 cohort. We confirmed an association of advanced parental and particularly paternal age with the occurrence of sporadic NF1.

Novel mutations in the NF1 gene in Czech patients with neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is one of the most common inherited human disorders, with an estimated incidence of 1 per 3500 births. In most cases, the disease is caused either by mutation in the NF1 gene, or by a particular or complete deletion of the NF1 gene. The NF1 gene exhibits one of the highest mutation rates of any human disorder. In this experimental study of the NF1 gene, we screened the mutational spectrum of 22 unrelated patients from the Czech Republic using the denaturing high-performance liquid chromatography (DHPLC) and multiplex ligation-dependent probe amplification (MLPA) methods. We found NF1 mutations in 17 patients: 15 causal mutations were detected with the use of the DHPLC method (15/20, 75%). With the MPLA method, we also confirmed and specified two large deletions that were previously genotyped by microsatellite markers. Twelve of the above mentioned mutations were newly found:c.1_2delATinsCC, c.1185+1G>C, c.1757_1760delCTAG, c.1642-7A>G, c.2329 T>G, c.2816delA, c.3738_3741delGTTT, c.4733 C>T, c.5220delT, c.6473_6474insGAAG, ex 14_49del, ex28_49del. We present this study as a first effectual step in the routine diagnosis of the NF1 in patients from the Czech Republic.

P139 – 3023: First epileptic seizures in children followed for cardiac rhabdomyomas and tuberous sclerosis

Objective Tuberous sclerosis (TSC) is a congenital multisystemic disease affecting also nervous system; including early onset of epilepsy and risk of mental retardation. Cardiac rhabdomyoma (CR) is the earliest diagnostic criterion of TSC. It belongs to the major diagnostic criteria of TSC. Finding of CR enables prenatal/early postnatal identification of children at risk of TSC and allows to follow up these children from early neonatal period. Methods 29 children with CR were followed up from 01/2002 to 01/2015 from neonatal age. Several clinical, EEG and neuroimaging characteristics were evaluated including age at seizure onset, types of seizures and psychomotor development in these children. Results Our series included 15 boys and 14 girls. In 26/29 (90%) children with CR the diagnosis of TSC was established. Two children with TSC died. Twenty-three (23/26, 88%) children with TSC have developed epilepsy, 18/23 (70%) of them within the first year of life and seizure types consisted of partial motor seizures (13/23), infantile spasms (5/23) and other generalized types of seizures (5/23). Early administration of antiepileptic drug(s) resulted in complete seizure control in 13/23 patiens. Mental retardation was proven in 14/26 TSC children; always in subjects with early manifestation of epilepsy. In 3/29 children with CR, the diagnosis of TSC was not established; no one of them developed epilepsy. Conclusion 1) Epilepsy starts in children with TSC usually before the first year of life. Seizures most often include partial motor, less frequently infantile spasms and other generalized types of seizures. 2) Mental retardation dominates in TSC children with early manifestation and difficultto-compensated epilepsy. 3) Children with CR who did not fulfill diagnostic criteria for TSC, have not developed epilepsy. 4) We suppose positive impact of early initiated antiepileptic treatment on the psychomotor development of these children with TSC. Supported by project 00064203-IG6005, project EPISTOP

FOCAL AREAS OF HIGH-SIGNAL INTENSITY ON BRAIN T2-WEIGHTED MAGNETIC RESONANCE IMAGING SCANS ARE SIGNIFICANT FOR THE DIAGNOSIS OF NEUROFIBROMATOSIS VON RECKLINGHAUSEN TYPE 1

INTRODUCTION: Neurofibromatosis von Recklinghausen type 1 (NF1) is characterized by the following National Institutes of Health (NIH) diagnostic criteria: café au lait spots, freckling, neurofibromas, Lisch nodules, optic glioma, distinct osseous lesions, and first-degree relative with NF1. Focal areas of high-signal intensity (FASI) in white matter and deep gray matter are typical brain MRI findings in children with NF1. OBJECTIVE: This study evaluated the frequency of FASI and the possibility of using FASI as a diagnostic criterion. METHODS: In a group of 160 children, the diagnosis of NF1 was confirmed in keeping with the NIH criteria. All children had MRI examination of the brain. The MRI findings of FASI in the children with NF1 were compared both with the brain MRI findings of the control group of 160 children with different diagnoses and with frequencies of the NIH diagnostic criteria. RESULTS: In 137 (86%) patients with NF1, ≥1 FASI were found. The difference between frequency of FASI in the NF1 group and in the control group (14 [9%]) is highly significant. The frequencies of the diagnostic criteria were as follows: café au lait spots: 157 (98%); freckling: 123 (77%); neurofibromas: 112 (70%); NF1 relatives: 89 (56%); Lisch nodules: 71 (44%); optic glioma: 45 (28%); and osseous lesions: 15 (9%; only partial examination of the group). CONCLUSIONS: The findings of FASI in T2-weighted images of the brain MRI are significantly frequent in children with NF1. Frequency of FASI is comparable with frequency of NIH diagnostic criteria. FASI could be proposed as an additional or new criterion for the NF1, mainly in childhood.