A. M. Cobo

Autosomal dominant lateral temporal epilepsy: Clinical and genetic study of a large basque pedigree linked to chromosome 10q

We report a large family with a temporal partial epilepsy syndrome inherited in an autosomal dominant mode, with a penetrance of about 80%. This epilepsy syndrome is benign, with age of onset in the second or third decade of life. It is characterized by rare partial seizures, usually secondarily generalized, arising mostly during sleep, without postictal confusion. There is a good response to the antiepileptic therapy but often a recurrence of seizures after drug withdrawal. The partial component, visual (lights, colors, and simple figures) or auditory (buzzing or “humming like a machine”), the existence of temporo‐occipital interictal electroencephalographic epileptiform abnormalities, and the hypoperfusion in the temporal lobe detected by interictal hexamethylpropyleneamine oxime–technetium 99m (HMPAO‐Tc99m) single‐photon emission computed tomography, strongly suggest a lateral temporal lobe origin. The genetic analysis found linkage to chromosome 10q, and localized a gene in a 15‐cM interval that overlaps a previously found localization for partial epilepsy in a large three‐generation family. This syndrome could be called autosomal dominant lateral temporal epilepsy. Ann Neurol 1999;45:182–188

Prevalence of myotonic dystrophy in Guipúzcoa (Basque Country, Spain)

Prevalence figures for inherited neuromuscular disorders are important both for health care planning purposes and for evaluating the need for DNA diagnostic services for eugenic approaches. We screened for the prevalence of myotonic dystrophy (MyD) through extensive inquiry of neurologic and primary health services of Guipúzcoa (Basque Country, northern Spain) between 1989 and 1991. Typical adult-onset and neonatal cases and relatives at risk, suffering from a partial syndrome, were included. In the latter, molecular typing was performed with DNA probes close to the MyD gene to demonstrate the MyD gene carrier status. The high prevalence detected (26.5 cases per 100,000 population) could be explained by methodological factors, but intrinsic factors, such as a possible founder genetic effect or the quick growth of the Guipúzcoa population since the last century may contribute to one of the highest MyD prevalences in the world. In the future, the methodological basis for epidemiologic surveys of MyD must combine molecular technology with more-extensive family inquiries.

Contribution of molecular analyses to the estimation of the risk of congenital myotonic dystrophy.

A molecular analysis of the maternal and child CTG repeat size and intergenerational amplification was performed in order to estimate the risk of having a child with congenital myotonic dystrophy (CMD). In a study of 124 affected mother-child pairs (42 mother-CMD and 82 mother-non-CMD) the mean maternal CTG allele in CMD cases was three times higher (700 repeats) than in non-CMD cases (236 repeats). When the maternal allele was in the 50-300 repeats range, 90% of children were non-CMD. In contrast, when the maternal allele was greater than 300 repeats, 59% inherited the congenital form. Furthermore, the risk of having a CMD child is also related to the intergenerational amplification, which was significantly greater in the mother-CMD pairs than in the mother-non-CMD pairs. Although the risk of giving birth to a CMD child always exists for affected mothers, our data show that such a risk is considerably higher if the maternal allele is greater than 300 repeats.

Screening of the CAPN3 gene in patients with possible LGMD2A

To the Editor: We included 42 unrelated patients (21 males and 21 females) for molecular analysis of the calpain-3 gene (CAPN3). Patients fulfilled clinical diagnostic criteria for autosomal recessive limb girdle muscular dystrophy type 2 A (LGMD2A, MIM #253600), and/or presented a decreased or absent calpain-3 protein on Western blot. DNA samples were collected after informed consent to comply with the ethical rules of the institutions involved. The 24 exons and flanking intronic boundaries of CAPN3 were PCR amplified, then analyzed for mutations by using a DHPLC-WAVE 3500HT apparatus (Transgenomic, Omaha, NE, USA). Subsequent sequencing of the abnormally eluted fragments was performed (on a ABI3130 sequencer; Applied Biosystems, Foster City, CA, USA). In cases where only one or no mutation was identified, the complete coding sequence of CAPN3 was directly sequenced. All patients were of European or North-African descent. Seven were issued from consanguineous unions and 11 had a familial history of LGMD with at least one affected sib. The remaining patients were isolated cases born from unrelated parents. In 35 out of 42 patients (83%), two pathogenic mutations were identified (Table 1), confirming the diagnosis of LGMD2A on a genetic basis. Sixteen patients carried a homozygous mutation, whereas the other 19 were found to be compound heterozygotes. In nine of these patients, the presence of a homozygous mutations in the absence of consanguinity, suggested the presence of recurrent pathogenic alleles rather than founder mutations. Nonetheless, in these cases, a possible hemizygosity due to deletions (1) on the opposite allele has not been formerly excluded yet as leading to a pseudo-homozygous sequence pattern. Among the patients for whom clinical data are available, the age at onset ranged from 5 to 47 years. At onset, 23 patients presented with typical LGMD and five with progressive muscular dystrophy. Western blot analyzes have been performed for 29 patients, demonstrating an absence or a severe decrease of calpain-3. Altogether, 76 mutations were identified including 46 different variations, 10 (22%) of them being novel (2) (Fig. 1a). The mutation type was as follows (Fig. 1b): 32 missense mutations (42%), 20 (26%) out of frame deletions and/or insertions, 18 mutations affecting splice sites (24%), four nonsense (5%), and two in frame deletions/insertions (3%). Among these mutations, 10 were unreported, and corresponded to five missense (which were not detected in 100 chromosomes from healthy controls), three frameshift deletions or insertions and two mutations affecting splicing sites. Ten recurrent mutations were identified: c.146G > A, c.883_886delGATAinsCTT, c.11949A > G, c.1250C > T, c.1714C > T, c.1865_ 1866delAG and c.1979A > G were each found in two patients, while c.2362_2363delAGins TCATCT and c.550delA were identified in three, and c.946-1G > A in four. These recurrent mutations account for 32% of all deleterious alleles. Most of the mutations identified in our study thus appear to be rare. This is consistent with the findings of Saenz and colleagues (3), who found a majority of non-recurrent mutations in their large series, most of them being novel and likely ‘private’ mutations. In a recent study, Fanin and colleagues (4) have shown that 87% of mutations were clustered in seven out of the 24 CAPN3 exons (N 1, 4, 5, 8, 10, 11, 21). Beside, in the Leiden Muscular Dystrophy Database (2), 72% of mutations are clustered within eight exons (N 1, 4, 5, 10, 11, 13, 21, 22). In the present report, among all the identified mutations, 80% were located within eight exons (N 1, 4, 7, 10, 11, 13, 19, 22) (Fig. 1c). As in other studies, we didn’t find any mutations in exons 12, 14, 18 and 24, but report a novel mutation in exon 23 (c.2420C > T, p.Ile807Thr), in which only one mutation has been recently found (2). The clustering of mutations seems to be correlated, somehow, to the Clin Genet 2006: 69: 444–449 Printed in Singapore. All rights reserved Copyright # Blackwell Munksgaard 2006

Frequency of myotonic dystrophy gene carriers in cataract patients.

DNA samples from 231 unselected patients with cataracts were studied to determine the frequency of the DM mutation in cataract patients. A previous epidemiological study established a high prevalence of DM in the population of Guipúzcoa (Basque Country, Spain), 26.5 cases/100,000. We have found two carriers (0.9%) of the DM mutation in patients who are not related to any previously known DM family. The screening of the DM mutation in cataract patients should be restricted to young patients or people with multicoloured and iridescent opacities, in which the risk of carrying the DM premutation could be higher. Our results suggest that subjects with 38 to 80 repeats could constitute the genetic reservoir of the DM mutation.

Frequency of intergenerational contractions of the CTG repeats in myotonic dystrophy.

Myotonic dystrophy (MD), an autosomal dominant multisystemic disorder with a high phenotypic variability, is the most common muscular dystrophy in adult life. The mutation underlying DM has been characterized as an expanded CTG trinucleotide repeat sequence in the 3′ untranslated region of a protein kinase gene on chromosome 19q13.2–13.3.

Detection of TRIM32 deletions in LGMD patients analyzed by a combined strategy of CGH array and massively parallel sequencing

Defects in TRIM32 were reported in limb-girdle muscular dystrophy type 2H (LGMD2H), sarcotubular myopathies (STM) and in Bardet-Biedl syndrome. Few cases have been described to date in LGMD2H/STM, but this gene is not systematically analysed because of the absence of specific signs and difficulties in protein analysis. By using high-throughput variants screening techniques, we identified variants in TRIM32 in two patients presenting nonspecific LGMD. We report the first case of total inactivation by homozygous deletion of the entire TRIM32 gene. Of interest, the deletion removes part of the ASTN2 gene, a large gene in which TRIM32 is nested. Despite the total TRIM32 gene inactivation, the patient does not present a more severe phenotype. However, he developed a mild progressive cognitive impairment that may be related to the loss of function of ASTN2 because association between ASTN2 heterozygous deletions and neurobehavioral disorders was previously reported. Regarding genomic characteristics at breakpoint of the deleted regions of TRIM32, we found a high density of repeated elements, suggesting a possible hotspot. These observations illustrate the importance of high-throughput technologies for identifying molecular defects in LGMD, confirm that total loss of function of TRIM32 is not associated with a specific phenotype and that TRIM32/ASTN2 inactivation could be associated with cognitive impairment.

Anticipation in Myotonic Dystrophy: A Parental-Sex-Related Phenomenon

We report anticipation in an extensive sample of myotonic dystrophy (MyD) kindreds taken from an epidemiological survey recently conducted in Guipúzcoa, Spain. Analysis of the parent-child pairs ascertained showed a mean anticipation of 2.86 decades (range 0-6). Greater anticipation occurred when the transmissor parent was the mother. These results suggest a possible sex-related effect in the transmission of the MyD gene, and are in agreement with recent discoveries at the molecular level.