Homozygous EXOSC3 mutation c.92G→C, p.G31A is a founder mutation causing severe pontocerebellar hypoplasia type 1 among the Czech Roma.

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.

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 father's age was higher than it was for the mother's 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.