Cognitive/personality pattern and triplet expansion size in adult myotonic dystrophy type 1 (DM1): CTG repeats, cognition and personality in DM1

BACKGROUND

Although central nervous system (CNS) involvement in adult myotonic dystrophy type 1 (DM1) was described long ago, the large number of variables affecting the cognitive and personality profile have made it difficult to determine the effect of DM1 on the brain. The aim of this study was to define the cognitive and personality patterns in adult DM1 patients, and to analyse the relationship between these clinical patterns and their association with the underlying molecular defect.

METHOD

We examined 121 adult DM1 patients with confirmed molecular CTG repeat expansion and 54 control subjects using comprehensive neuropsychological tests and personality assessments with the Millon Clinical Multiaxial Inventory (MCMI)-II. We used a multiple linear regression model to assess the effect of each variable on cognition and personality adjusted to the remainders.

RESULTS

Patients performed significantly worse than controls in tests measuring executive function (principally cognitive inflexibility) and visuoconstructive ability. In the personality profile, some paranoid and aggressive traits were predominant. Furthermore, there was a significant negative correlation between the CTG expansion size and many of the neuropsychological and personality measures. The molecular defect also correlated with patients' daytime somnolence.

CONCLUSIONS

Besides muscular symptomatology, there is significant CTG-dependent involvement of the CNS in adult DM1 patients. Our data indicate that the cognitive impairment predominantly affects the fronto-parietal lobe.

LGMD2A: genotype-phenotype correlations based on a large mutational survey on the calpain 3 gene

We present here the clinical, molecular and biochemical findings from 238 limb-girdle muscular dystrophy type 2A (LGMD2A) patients, representing approximately 50% (238 out of 484) of the suspected calpainopathy cases referred for the molecular study of the calpain 3 (CAPN3) gene. The mean age at onset of LGMD2A patients was approximately 14 years, and the first symptoms occurred between 6 and 18 years of age in 71% of patients. The mean age at which the patients became wheelchair bound was 32.2 years, with 84% requiring the use of a wheelchair between the age of 21 and 40 years. There was no correlation between the age at onset and the time at which the patient became wheelchair bound, nor between the sex of the patient and the risk of becoming wheelchair bound. Of the cases where the CAPN3 gene was not affected, approximately 20% were diagnosed as LGMD2I muscular dystrophy, while facioscapulohumeral muscular dystrophy (FSHD) was uncommon in this sample. We identified 105 different mutations in the CAPN3 gene of which 50 have not been described previously. These were distributed throughout the coding region of the gene, although some exons remained free of mutations. The most frequent mutation was 2362AG-->TCATCT (exon 22), which was present in 30.7% of the chromosomes analysed (146 chromosomes). Other recurrent mutations described were N50S, 550DeltaA, G222R, IVS6-1G-->A, A483D, IVS17+1G-->T, 2069-2070DeltaAC, R748Q and R748X, each of which was found in >5 chromosomes. The type of mutation in the CAPN3 gene does not appear to be a risk factor for becoming dependent on a wheelchair at a determined age. However, in the cases with two null mutations, there were significantly fewer patients that were able to walk than in the group of patients with at least one missense mutation. Despite the fact that the results of phenotyping and western blot might be biased due to multiple referral centres, producing a diagnosis on the basis of the classical phenotype is neither sufficiently sensitive (86.7%) nor specific (69.3%), although western blot proved to be even less sensitive (52.5%) yet more specific (87.8%). In this case LGMD2I was a relevant cause of false-positive diagnoses. Considering both the clinical phenotype and the biochemical information together, the probability of correctly diagnosing a calpainopathy is very high (90.8%). However, if one of the analyses is lacking, the probability varies from 78.3 to 73.7% depending on the information available. When both tests are negative, the probability that the sample comes from a patient with LGMD2A was 12.2%.

PIP2 binding residues of Kir2.1 are common targets of mutations causing Andersen syndrome

BACKGROUND

Mutations in KCNJ2, the gene encoding the inward-rectifying K+ channel Kir2.1, cause the cardiac, skeletal muscle, and developmental phenotypes of Andersen-Tawil syndrome (ATS; also known as Andersen syndrome). Although pathogenic mechanisms have been proposed for select mutations, a common mechanism has not been identified.

METHODS

Seventeen probands presenting with symptoms characteristic of ATS were evaluated clinically and screened for mutations in KCNJ2. The results of mutation analysis were combined with those from previously studied subjects to assess the frequency with which KCNJ2 mutations cause ATS.

RESULTS

Mutations in KCNJ2 were discovered in nine probands. These included six novel mutations (D71N, T75R, G146D, R189I, G300D, and R312C) as well as previously reported mutations R67W and R218W. Six probands possessed mutations of residues implicated in binding membrane-associated phosphatidylinositol 4,5-bisphosphate (PIP2). In total, mutations in PIP(2)-related residues accounted for disease in 18 of 29 (62%) reported KCNJ2 -based probands with ATS. Also reported is that mutation R67W causes the full clinical triad in two unrelated males.

CONCLUSIONS

The novel mutations corresponding to residues involved in Kir2.1 channel-PIP2 interactions presented here as well as the overall frequency of mutations occurring in these residues indicate that defects in PIP2 binding constitute a major pathogenic mechanism of ATS. Furthermore, screening KCNJ2 in patients with the complex phenotypes of ATS was found to be invaluable in establishing or confirming a disease diagnosis as mutations in this gene can be identified in the majority of patients.

Myopathy with lobulated muscle fibers: evidence for heterogeneous etiology and clinical presentation

The clinico-pathological features of 17 patients displaying a myopathy with lobulated (trabeculated) fibers are reported. All these patients had a limb girdle phenotype and at least 20% of lobulated fibers in their muscle biopsies. There were ten females and seven males. The onset of symptoms ranged from 2 to 55 years (mean 24). The average age at the time of muscle biopsy was 39 (range 3-63). Interestingly, in six patients, high prevalence of lobulated fibers was observed at the second biopsy only, performed on average 11 years after the first or in another muscle. Six patients had a suggestively positive family history. Facial weakness was noted in two patients (genetic study confirmed FSH dystrophy). The course and the severity of weakness varied from one patient to another. Immunohistochemistry and Western blot analyses revealed one Duchenne carrier, one alpha-sarcoglycanopathy, no dysferlinopathy and four calpain deficiencies (including one patient with FSH dystrophy), but SSCP revealed mutation in the calpain gene in only one of the patients. These results show that (1) myopathies with lobulated fibers are clinically and genetically heterogeneous, (2) lack of calpain expression by Western blot analysis is not always associated with null mutation, (3) a molecular diagnosis is made in less than 40% of myopathy with lobulated fibers, (4) when observed, lobulated fibers are most prominent in proximal muscles and require time to appear.

Autosomal dominant nocturnal frontal lobe epilepsy in a Spanish family with a Ser252Phe mutation in the CHRNA4 gene

BACKGROUND

A large family with autosomal dominant nocturnal frontal lobe epilepsy from the south of Spain was studied. The clinical appearance of the disease in this family, which included 28 members, of whom 11 were affected and 2 were obligate carriers, was identical to that previously described in an Australian family and a Norwegian family, in which mutations in exon 5 of the CHRNA4 gene were found.

METHODS

Following DNA extraction, the family was genotyped with 4 fluorescent markers flanking the locus to the CHRNA4 gene on chromosome 20q13.3, and lod score computations were performed. The exon 5 of the CHRNA4 gene was amplified between nucleotides 535 and 825 and polymerase chain reaction products were purified and sequenced directly.

RESULTS

The same missense mutation as that found in the Australian family, C-->T, which causes the replacement of a serine with phenylalanine in amino acid 252 in exon 5, was detected. This mutation segregated with the disorder in all 11 affected members, in the 2 obligate carriers, and in 1 asymptomatic sibling, and was not found in 1 spouse and 1 daughter. Neither of the 2 polymorphisms found in a series of families with epilepsy were found in our sample [corrected].

CONCLUSIONS

These data confirm the clinical homogeneity in the phenotypic expression of autosomal dominant nocturnal frontal lobe epilepsy caused by mutation in the CHRNA4 gene, and the pathogenic role of the Ser252Phe mutation in this disorder.

Calpainopathy-a survey of mutations and polymorphisms

Limb-girdle muscular dystrophy type 2A (LGMD2A) is an autosomal recessive disorder characterized mainly by symmetrical and selective atrophy of the proximal limb muscles. It derives from defects in the human CAPN3 gene, which encodes the skeletal muscle-specific member of the calpain family. This report represents a compilation of the mutations and variants identified so far in this gene. To date, 97 distinct pathogenic calpain 3 mutations have been identified (4 nonsense mutations, 32 deletions/insertions, 8 splice-site mutations, and 53 missense mutations), 56 of which have not been described previously, together with 12 polymorphisms and 5 nonclassified variants. The mutations are distributed along the entire length of the CAPN3 gene. Thus far, most mutations identified represent private variants, although particular mutations have been found more frequently. Knowledge of the mutation spectrum occurring in the CAPN3 gene may contribute significantly to structure/function and pathogenesis studies. It may also help in the design of efficient mutation-screening strategies for calpainopathies.

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.

[Alterations in functional proteins. Calpaine-3 deficiency]

INTRODUCTION

Muscular dystrophies due to calpain deficiency are the first example of a muscular dystrophy due to the mutation of a gene codifying for a non-structural enzymatic protein of unknown function and substrate.

DEVELOPMENT

More than 70 mutations have been described in the gene structure, localized to chromosome 15. Although the time course and topography is fairly homogeneous, correlation between the different mutations and the phenotype has still to be analyzed. The age of onset of symptoms is usually between 8 and 14, with no difference between the sexes. There is a slow but uniformly progressive course starting in the pelvis and extending to the shoulder and the distal musculature. Almost all patients are confined to a wheelchair twenty years after onset of the disease. There is no facial, oculomotor or bulbar involvement and gemellar pseudohypertrophy is rare. However, a winged scapula and marked lumbar hyperlordosis is universal. No cardiac or cognitive changes have been observed. Muscle CT shows a pattern of atrophy, mainly of the posterior and medial muscle compartments and of the posterosuperficial group of the legs, which varies depending on the time the disorder has been present. This condition is the commonest etiological group of the dystrophy syndromes, especially of those of late infancy or juvenile onset, in the open populations studied to date. Muscle biopsy, stained by all methods available, is essential to rule out other types of progressive dystrophies secondary to deficiencies of structural proteins.

Limb-girdle muscular dystrophy in Guipúzcoa (Basque Country, Spain)

The concept of limb-girdle muscular dystrophy (LGMD) is changing rapidly due to the advances in molecular genetics. Recently, seven different gene loci have been described, demonstrating that limb-girdle muscular dystrophy is a heterogeneous syndrome, which includes different diseases with a similar phenotype. In isolated populations which have little genetic exchange with neighbouring populations, an accumulation of cases may be found. We carried out an epidemiological study in Guipúzcoa, a small mountainous Basque province in northern Spain, and found the highest prevalence rate of LGMD described so far: 69 per million. Genetic studies demonstrated that 38 cases corresponded to the LGMD2A type, due to calpain-3 gene mutations. Only one patient with alpha-sarcoglycanopathy was found, and in 12 patients the genetic defect was not identified. Moreover, the particular calpain-3 mutation predominant in Basque chromosomes (exon 22, 2362AG-->TCATCT), has only been rarely found in the rest of the world. This observation strongly suggests a founder effect in the indigenous population of Guipúzcoa. The clinical characteristics of the patients with calpain-3 gene mutations were quite homogeneous and different from the other groups (sarcoglycanopathy and unknown gene defect), allowing for a precise clinical diagnostic. The disease onset was between the ages of 8 and 15 years, in most cases in the pelvic girdle, and the patients became wheelchair-bound between 11 and 28 years after onset. No pseudohypertrophy of calves or contractures were observed. No clear correlations were found between the nature and site of the mutation and the resulting phenotype.

[Muscular dystrophy due to a mutation in the gene of alpha-sarcoglycan subunit of dystrophin associated protein complex]

Linkage studies have confirmed the existence of clinical an genetic heterogeneity among the muscular dystrophies due to adhalin deficiency. We present the clinical, histological and genetic characteristics in a case of primary adhalinopathy (deficiency of the 50 kD subunit or alpha-sarcoglycan). It was a 19 years-old woman, born of non consanguineous parents, who shows a long evolution myopathy with onset before age 7, a severe evolution and becoming wheelchair bound at 10 years. She showed evident calf pseudohypertrophy and serum creatinkinase (CK) levels were elevated (40-180 times the standard level). The histological pattern showed a destructed fascicular architecture in agreement with severe muscular dystrophy, normal staining with anti-dystrophin monoclonal antibodies and abnormal staining pattern with anti-adhalin antibodies. The molecular study evidenced an homozygous point mutation (Arg-->Cys) at position 77 of exon 3 of the gene coding for the 50 kD subunit of the alpha-sarcoglycan complex localised in chromosome 17. In the light of this case, we suggest a revision of the diagnostic orientation in the muscular dystrophies and we review the new taxonomy of the limb-girdle muscular dystrophies, remarking the clinical signs which could indicate a given genetic locus.

[Neuropathy associated with arteriosclerosis]

OBJECTIVE

To determine the frequency and characteristics of the neuropathy associated with arteriosclerosis.

MATERIAL AND METHODS

A prospective clinical and electrophysiological study was made of 29 male patients with arteriosclerosis, in whom other causes of polyneuropathy had been excluded.

RESULTS

Eleven patients complained of paresthesiae (mostly mild). In 11 patients there were signs of polyneuropathy on clinical examination. Neurophysiological studies were abnormal in 11 patients, suggesting the presence of predominantly sensitive axonal neuropathy. In five patients with paresthesiae both physical examination and electrophysiological studies were normal. In 17 patients there were changes in the somatosensory evoked potentials. The brainstem auditory evoked potentials of 27 patients were suggestive of diffuse changes in central nervous conduction, together with super-imposed focal lesions. There were no differences as regards age, signs of disease in the legs or of the involvement of widespread illness, whether they were smokers, ex-smokers or non-smokers, the number of cigarettes smoked daily or the total duration of the smoking habit between the patients with and without clinical or electrophysiological polyneuropathy.

CONCLUSIONS

Approximately one third of the patients with arteriosclerosis have clinical or electrophysiological signs suggestive of predominantly sensitive axonal polyneuropathy. In some cases the patients had paresthesia but no changes were seen on physical or electrophysiological examination. The evoked potentials showed diffuse changes in central nervous conduction, and in some cases this was associated with signs of focal lesions.

Peripheral neuropathy associated with polycythemia vera

The aim of this study was to determine the frequency and characteristics of peripheral neuropathy associated to polycythemia vera. A prospective clinical and electrophysiological study was performed of 28 patients with polycythemia vera. Other causes of neuropathy were excluded. Eleven patients experienced paresthesiae, which were usually mild. In 13 (46%) patients, clinical examination revealed features suggesting polyneuropathy. Nerve conduction indexes were abnormal in 20 (71%) patients, suggesting the presence of a predominantly sensory axonal polyneuropathy. In the somatosensory evoked potentials a delay of the P40 wave was seen in 17 patients, while 11 exhibited a delay of the N20 wave. Three of these patients also showed bilateral increases in the I-III, I-V and III-V intervals of brain-stem evoked potentials. In most cases, the delay was moderate and symmetrical. No differences in sex, age, duration of disease, hematocrit values, or platelet counts were found between patients with or without clinical or electrophysiological polyneuropathy. A high percentage of patients with polycythemia vera present clinical or electrophysiological signs of predominantly sensory axonal polyneuropathy which is probably secondary to ischemia, due to increased blood viscosity and platelet dysfunction.

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. We have analyzed the presence of CTG intergenerational variations on transmission in parent-child pairs affected with DM. The series includes 90% of all living affected descendants (symptomatic or asymptomatic) from a given myotonic dystrophy (DM) patient. A contraction of the CTG repeat size was observed in ten parent-child pairs (14.1%) and remained unchanged in five (7%) pairs. The number of CTG repeats decreased in 2/30 maternal transmissions (6.7%) and in 8/41 paternal transmissions (19.5%). We found 14 asymptomatic individuals carrying the CTG expansion among the offspring. In six of them, a contraction of the CTG repeat was observed, and in all six cases, the DM allele was paternally transmitted. Since nearly all the asymptomatic family members of DM patients were analyzed in this series, the observed percentage of contractions can be considered more realistic, even though the number of parent-child pairs is small.

[Diseases due to instability of DNA]

The catalog of genetic diseases whose mutational mechanisms are based on the expansion of nucleotide triplets includes 8 disorders classified in terms of type of triplet sequence and the mechanism by which the mutation manifests clinically. To date there are 3 groups. The first is made up of several mental retardation syndromes linked to fragility in the X chromosome (FRAXA, FRAXE, FRAXF, FRA16), with CGG type triplets and large growth expansions located close to a CpG island whose methylation determines degree of chromosome fragility as well as the size of expansion. The second group encompasses diseases arising from CAG triplets. Examples are spinal bulbar atrophy, Huntington's chorea (HC), type 1 dominant cerebellar ataxia (DCA1), dentatorubral-pallidoluysian atrophy (DRPLA) and Machado-Joseph's disease. In this group the expansion codes a polyglutamate residue that gives rise to clinical manifestations by way of functional gain. Myotonic dystrophy (MD) remains in a separate group, with large-size expansion but no chromosomal fragility, and clinical manifestations in multiple systems. All entities encompass phenotypic variation or tendency to inter-generational growth of the expanded fragment that triggers the anticipation phenomenon to varying degrees--greater for some diseases (MD) in cases of maternal transmission and for others (DCA1, HC and DRPLA) when transmission is paternal. The mechanisms by which expansions occur is unknown but the decisive element in some entities may be failure to correct errors in DNA duplication and errors in the integrity of the repeated sequence. We review the difficulties inherent in establishing correlations between genotype and phenotype and in providing genetic counseling.

Influence of the sex of the transmitting grandparent in congenital myotonic dystrophy

To analyse the influence of the sex of the transmitting grandparents on the occurrence of the congenital form of myotonic dystrophy (CDM), we have studied complete three generation pedigrees of 49 CDM cases, analysing: (1) the sex distribution in the grandparents' generation, and (2) the intergenerational amplification of the CTG repeat, measured in its absolute and relative values, between grandparents and the mothers of CDM patients and between the latter and their CDM children. The mean relative intergenerational increase in the 32 grandparent-mother pairs was significantly greater than in the 56 mother-CDM pairs (Mann-Whitney U test, p < 0.001). The mean expansion of the grandfathers (103 CTG repeats) was also significantly different from that seen in the grandmothers' group (154 CTG repeats) (Mann-Whitney U test, p < 0.01). This excess of non-manifesting males between the CDM grandparents' generation with a smaller CTG length than the grandmothers could suggest that the premutation has to be transmitted by a male to reach the degree of instability responsible for subsequent intergenerational CTG expansions without size constraints characteristic of the CDM range.

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.

Characteristics of intergenerational contractions of the CTG repeat in myotonic dystrophy

In myotonic dystrophy (DM), the size of a CTG repeat in the DM kinase gene generally increases in successive generations with clinical evidence of anticipation. However, there have also been cases with an intergenerational contraction of the repeat. We examined 1,489 DM parent-offspring pairs, of which 95 (6.4%) showed such contractions in peripheral blood leukocytes (PBL). In 56 of the 95 pairs, clinical data allowed an analysis of their anticipation status. It is surprising that anticipation occurred in 27 (48%) of these 56 pairs, while none clearly showed a later onset of DM in the symptomatic offspring. The contraction occurred in 76 (10%) of 753 paternal transmissions and in 19 (3%) of 736 maternal transmissions. Anticipation was observed more frequently in maternal (85%) than in paternal (37%) transmissions (P < .001). The parental repeat size correlated with the size of intergenerational contraction (r2 = .50, P << .001), and the slope of linear regression was steeper in paternal (-.62) than in maternal (-.30) transmissions (P << .001). Sixteen DM parents had multiple DM offspring with the CTG repeat contractions. This frequency was higher than the frequency expected from the probability of the repeat contractions (6.4%) and the size of DM sib population (1.54 DM offspring per DM parent, in 968 DM parents). We conclude that (1) intergenerational contractions of the CTG repeat in leukocyte DNA frequently accompanies apparent anticipation, especially when DM is maternally transmitted, and (2) the paternal origin of the repeat and the presence of the repeat contraction in a sibling increase the probability of the CTG repeat contraction.

[Direct genotypic analysis of myotonic dystrophy: detection of an unstable DNA fragment in carriers]

BACKGROUND

Myotonic dystrophy (DM) is an inherited autosomal dominant disorder. The molecular defect responsible for the disease is the expansion of a CTG triplet at the 3' end of the DM gene. We report the analysis of the gene expansion, its correlation with the clinical severity and with the phenomenon of anticipation.

METHODS

Using the cDNA25 probe, we have analyzed 140 affected DM patients from a total of 42 families comprising 303 individuals. According to the clinical status, the affected DM patients were classified as follows: group I, congenital form; group II, classical form, and group III, mild form.

RESULTS

A larger than normal fragment was detected in all the DM patients but in none of the controls. The expansion size is 2.5-6 kb in group I, 0.3-5 kb in group II and 0.2-1.5 kb in group III. In 49 parent-child couples which show clinical anticipation, 47 have an increase in size of the fragment from one generation to the next.

CONCLUSIONS

Our results show a clear correlation between the severity of the disease and the expansion size. We confirm at the molecular level the phenomenon of anticipation. The direct gene analysis of the DM families allows the diagnosis of all the at-risk individuals and facilitates the genetic counselling of these families.

[Application of the polymerase chain reaction technique (PCR) to the molecular diagnosis of myotonic dystrophy]

We report the application of the PCR technique to study the CKMM polymorphisms in 39 Spanish Myotonic Dystrophy affected families. We have studied 255 subjects comprising 116 clinically affected DM patients. The molecular study was informative in 64% of the DM patients. For the 76 at risk individuals, the study was informative in 46 of them, confirming the non carrier status in 34 individuals and demonstrating the at risk haplotype in 12. In the remaining 30 subjects, it was not possible to establish a diagnose with this technique exclusively. The use of the CKMM probe in the DM genetic studies was extremely useful because of the close linkage with the gene (1 cM) and the high heterozygosity (PIC = 0.33). The allelic frequencies detected by the TaqI enzyme (allele I = 0.27; allele i = 0.73) and NcoI enzyme (allele J = 0.29; allele j = 0.71) are similar to the previously reported in other european populations.

[Prenatal diagnosis of myotonic dystrophy: the first experience in Spain]

We report the first prenatal diagnosis of myotonic dystrophy (MD) in Spain by DNA techniques. The previous familiar study allowed us to determine the DM haplotype in this family with the following probe/enzyme combinations: p4.1/Msp I, LDR 152/Bgl II, Apo CII/Ban I, Taq I, Bam HI, pSCII/Bgl I. In the tenth week of amenorrhea, a transabdominal biopsy was done to obtain chorionic villi. One part of the sample was processed for the cytogenetic analysis that revealed a 46 XY karyotype. The other part was used to perform the molecular analysis with two probes, p4.1 and LDR 152, determining that the fetus was a DM gene carrier with a 96% probability.

[Genetic analysis of Spanish families with myotonic dystrophy]

Myotonic dystrophy (MD) is the most common form of muscular dystrophy in adult life, with a clinical prevalence of 5.5/100,000, being the gene prevalence of 13.5. The disease is autosomal dominant with variable expressivity, existing a congenital form with a severe prognosis. Recent genetic studies revealed that the DM gene is localized in the chromosome's 19 proximal long arm and with recombinant DNA techniques, several polymorphic markers have been isolated near the gene, the closet being Apo-CII, LDR 152 and p 4.1. We have studied clinically, electrophysiologically and by genetic analysis 6 families with 32 individuals. We have diagnosed the disease in 16 individuals and after the molecular analysis, the DM gene was totally excluded in 6 clinically healthy individuals. In our preliminary study, the use of Msp I/p 4.1, Bgl II/LDR 152 y Ban I, Bgl I, Taq I/Apo-CII c-DNA and genomic was found the most informative combination. These molecular analysis seem to be very useful as a complement to the diagnosis of myotonic dystrophy.