The Sjögren-Larsson syndrome gene is close to D17S805 as determined by linkage analysis and allelic association.

Sjögren-Larsson Syndrome (SLS) is characterized by congenital ichthyosis, spastic dior tetraplegia and mental retardation. It is an autosomal recessive trait that is frequent in the northern part of Sweden. Based on linkage analysis and allelic association, the disorder has now been mapped to chromosome 17. Meiotic recombinations suggest that the gene is flanked by D17S805 on the centromeric and D17S783, D17S959, D17S842 and D17S925 on the telomeric side. These markers map to the same location in reference pedigrees. Strong allelic association (chi-square 60.28, p < 0.0003) to D17S805 suggests that the mutation is located close to this marker.

Re-evaluation of the dysequilibrium syndrome.

OBJECTIVES: To re-evaluate middle-aged Swedish patients diagnosed with dysequilibrium syndrome (DES) in childhood and to compare their clinical and neuroimaging features to DES with VLDLR gene mutations (DES-VLDR). MATERIALS AND METHODS: Six patients from five families underwent neurological examination and magnetic resonance imaging (MRI) of the brain. Blood samples from the patients were screened for serum carbohydrate-deficient transferrin (s-CDT; disialotransferrin). The very-low-density lipoprotein receptor (VLDLR) gene was sequenced. RESULTS: Five patients had non-progressive cerebellar ataxia (NPCA), dysarthria and short stature. Mental retardation and strabismus, characteristic for DES-VLDLR, were inconsistent among our patients. None of our patients had VLDLR mutations or MRI findings characteristic of DES-VLDLR. MRI findings were variable from a normal cerebellum to marked cerebellar hypoplasia or atrophy and signal intensity changes. One patient was diagnosed with congenital disorder of glycosylation type 1a (CDG-1a). CONCLUSIONS: DES was originally coined on mainly clinical grounds before MRI and specific genetic tests were available, both of which should be used to arrive at an appropriate diagnosis.

Prevalence of beta-thalassaemia and sickle cell traits in premarital screening in Al-Qassim, Saudi Arabia.

To study the prevalence of beta-thalassaemia and sickle cell traits in the Al-Qassim region, Saudi Arabia. The Ministry of Health of Saudi Arabia launched a countrywide programme in February 2004 to allow all Saudis planning marriage to screen their carrier status for beta-thalassaemia and sickle cell traits. This population survey of mandatory premarital screening for beta-thalassaemia and sickle cell heterozygotes provided an opportunity to estimate the prevalence of these traits in the Al-Qassim region. From February 2004 to October 2006 all individuals attending for premarital screening in that region were screened. For each subject, venous blood was taken to determine complete blood count, red cell indices and hemoglobin electrophoresis. Subjects were considered to have beta-thalassaemia trait if mean corpuscular volume was <79 fl, mean corpuscular haemoglobin <27 pg and haemoglobin A2 level >3.5%; and sickle cell trait if sickle cell haemoglobin amounted to 35 to 45% and sickling test was positive. Totally 38,153 individuals were screened during the study period. The prevalence rates of beta-thalassaemia and sickle cell traits were 0.165% (63/38,153) and 0.252% (96/38,153) respectively. Compared with results of previous studies carried out in this region on the same issue, the prevalence of sickle cell heterozygotes seems to be the same but the frequency of beta-thalassaemia carriers is substantially higher. Screening for carriers both of beta-thalassaemia and sickle cell traits is important to prevent at risk marriages through genetic counseling.

Strong founder effect for the fragile X syndrome in Sweden.

We analyzed the FRAXAC2 and DXS548 microsatellites in normal and fragile X chromosomes from Sweden and the Czech Republic in order to investigate a possible founder effect for chromosomes carrying a fragile X mutation. We report a much stronger linkage disequilibrium between the marker haplotypes and the disease in Swedish fragile X chromosomes than in Czech and most other previously studied Caucasian populations. Two haplotypes accounted for 64% of Swedish fragile X chromosomes and for only 14% of normal chromosomes. Neither of these two haplotypes was found in Czech chromosomes, but the most common Swedish fragile X haplotype is the same as that reported to be predominant in Finnish fragile X patients. Linkage disequilibrium was observed in the Czech fragile X chromosomes but the haplotypes were more diverse and similar to those observed in other Caucasian populations. The most prevalent Swedish fragile X haplotype was traced back from affected males to common ancestors in the early 18th century. This indicates an apparently silent segregation of fragile X alleles through up to nine generations. The geographical distribution of the two major at-risk haplotypes in Sweden suggests that they were present among early settlers in different parts of the country.

Prevalence of the fragile-X syndrome in mentally retarded boys in a Swedish county.

In an etiological study of an unselected series of mentally retarded children (IQ less than 70) born 1959-1970 in a northern Swedish county, 12 of 205 boys (5.9%) were found to have a fragile site on the distal end of the C-chromosome (fra (X) (q27]. The incidence of the fra (X) syndrome was calculated to be 1:1500 boys in this county. If this is true for the whole of Sweden, 30-40 new cases of the fra (X) syndrome should be born yearly in Sweden. This must be considered a minimum figure, since a certain proportion of individuals with fra (X) are not observed in groups of mentally retarded patients. Next to trisomy 21, the fragile X syndrome is the most common specific cause of mental retardation among mentally retarded boys in Sweden.

Fragile X families in a northern Swedish county--a genealogical study demonstrating apparent paternal transmission from the 18th century.

Eleven families including 35 cases with fra(X) mental retardation (MR) were traced genealogically using the Research Archives at Umeå University. Seven of the cases were women with fra(X). All of the families originated partly or totally from the county of Västerbotten. It was possible to link 7 of the index families to common ancestors over an 8-11 generation span. The remaining 4 families were not traced to the same ancestors. However, they were linked together pair-wise over a 7-8 generation span. Transmission of the fra(X) mutation was studied in these families. In the pedigree analyses, priority was given to maternal transmission. In 2 families the fra(X) mutation was transmitted solely through females over 7 or 8 generations respectively. Within 9 families the mutation was transmitted by males in 2-5 generations in order to reach common ancestors.

Fragile X families in a northern Swedish county: a genealogical study of possibly affected individuals in the nineteenth century.

Most studies of fragile X [fra(X)] families are able to document mental impairment only by family history. Using Swedish historical archives and the unique parish catechetical meeting records it is possible to document qualitative phenomena such as literacy for over 100 years. In this way it was possible to identify 7 individuals with mental retardation living in the nineteenth century in an earlier published fra(X) pedigree. Four of them were female. At the present time another 4 severely mentally retarded females with the fra(X) syndrome have been diagnosed in this family. The high prevalence of mentally retarded females might indicate a variant form of the fra(X) syndrome in this family.

Infantile autism and the fragile X. A Swedish multicenter study.

In a Swedish multicenter study of 122 cases of infantile autism, 16 boys (13%) were found to be fragile (X) (q27) positive. None of the 21 girls studied were fragile (X) positive.

Identification of mutations in the CACNL1A3 gene in 13 families of Scandinavian origin having hypokalemic periodic paralysis and evidence of a founder effect in Danish families.

Familial hypokalemic periodic paralysis (hypoPP) is an autosomal dominant disorder characterised by episodic attacks of paralysis of varying severity. Recently, linkage was found to markers in 1q31-32 and to the gene encoding the muscle DHP-sensitive calcium channel alpha 1-subunit (CACNL1A3). Subsequently, three mutations in this gene were identified in patients with hypoPP: Arg528His, Arg1239His and Arg1239Gly. In this study, two different mutations were found in the CACNL1A3 gene in 13 Scandinavian families, 10 of whom have the Arg528His mutation while 3 families have the Arg1239His. Furthermore, there is evidence of a founder effect in 8 of the 9 Danish hypoPP families investigated, consisting of haplotypes of microsatellite markers close to and within the CACNL1A3 gene and of the geographic origin of the families. For the first time, reduced penetrance in males with the Arg528His mutation was found in several cases.

Infantile autism--fragile X: molecular findings support genetic heterogeneity.

Twenty-two members of 18 families with autism have been examined for the presence of mutations and abnormal methylation in the FMR-1 region at Xq27.3. All patients fulfilled diagnostic criteria of infantile autism. A characteristic pattern of insertion and methylation were detected after Southern blot analysis in 7 autistic individuals expressing the fragile site at Xq27.3. Normal DNA patterns were observed in 15 autistic boys cytogenetically negative for the fragile site. The results indicate a lack of involvement of the FMR-1 region in infantile autists negative for fragile X expression.

Carrier detection of the fragile X syndrome using flanking loci DXS98, DXS105, and DXS304.

Diagnosis of the carrier status of the fragile X [fra(X)] syndrome was made in 2 unrelated women who did not express the fragile site. Both were related to several individuals with a typical fra(X) phenotype and the marker X chromosome. A restriction fragment length polymorphism (RFLP) approach was used with probes that flank the fra(X) locus (FRAXA). The loci used for risk calculations of the fra(X) genotype were DXS98 and DXS105 on the centromeric side and a recently characterized locus, DXS304, on the telomeric side. Coincidence correction for the distances between marker loci and FRAXA was made according to the Kosambi function. The DNA marker test gave the risk for one female to be a carrier of 99.7-99.9%. In another family a female was excluded from being a carrier with a probability of greater than 99.7%. The DNA marker U6.2, defining the locus DXS304, has increased the reliability of DNA based diagnosis of carrier status for females-at-risk. It is concluded that DNA analysis can serve as a valuable complement to chromosome analysis in families informative for the more closely linked flanking markers.

New X-linked syndrome with severe mental retardation, severely impaired vision, severe hearing defect, epileptic seizures, spasticity, restricted joint mobility, and early death.

A family with an X-linked mental retardation syndrome involving seven children in two generations is reported. The syndrome includes microcephaly, severe mental retardation, optic atrophy with severely impaired vision or blindness, a severe hearing defect, spasticity, epileptic seizures, restricted movement of the large joints, and death in infancy or early childhood. We conclude that this is a distinct, previously unrecognized X-linked mental retardation syndrome.

Methylation and mutation patterns in the fragile X syndrome.

Chromosomes carrying the mutation causing the fragile X [fra(X)] syndrome have been shown to have an unstable DNA sequence close to or within the fragile site. The length variation is located within a DNA fragment containing a CGG trinucleotide repeat which is unstable in both mitosis and meiosis. We have used the probe StB12.3 from the region to analyze the mutations and the methylation patterns in 21 families segregating for the fra(X) syndrome. Among 40 fra(X) males all showed an abnormal pattern. The normal 2.8 kb band was absent in 36 individuals and replaced by a heterogeneous smear of larger size. The remaining four were shown to be "mosaics" with the presence of both mutated, unmethylated and mutated, methylated fragments. We found four normal transmitting males, one which was a great-grandson of another normal transmitting male indicating that the pre-mutation can remain stable through two meioses in the female. In nine fra(X) positive females the abnormal pattern consisted of a smear, usually seen in affected males, in addition to the normal bands. Five of these females were mentally normal. Of clinical importance is the prediction of mental impairment in females. We suggest that this is not made by the detection of the full mutation alone, but rather by the degree of methylation of the normal X chromosome. Our results suggest that difference of clinical expression in monozygotic twins may be correlated with difference in methylation pattern. Six out of 33 fra(X) negative females at risk were diagnosed as carriers. Our observations indicate that molecular heterogeneity is responsible for variable expression of the fra(X) syndrome in both males and females.

Collaborative prospective study of the fragile X syndrome: one-year progress report.

A prospective study of the fragile X syndrome [fra(X)] was initiated one year ago to refine the estimates of recurrence risks based on the phenotype of the mother and the family history of the syndrome. The basic unit of data consists of the description of the conceptus of women known to carry the fra(X) gene or of mothers of an isolated case. To date, information on 261 women and their conceptuses was ascertained primarily through prenatal diagnosis; these data are summarized here. Although tests of significance were limited due to small sample sizes in subgroups, the following trends were observed: 1) the penetrance of fra(X) site expression was 80% in both male and female conceptuses suggesting that fra(X) site expression is equally penetrant early in development; 2) the sex ratio at the time of prenatal diagnosis did not differ from one, indicating that selection against fra(X) fetuses, if any, does not differ among sexes; 3) the recurrence risk among offspring of borderline/mildly retarded mothers was higher than that among offspring of intellectually normal mothers; 4) the recurrence risk in offspring did not differ based on the mother's fra(X) site expression; and 5) the recurrence risk in offspring of mothers with isolated cases was slightly less (34%) than that of obligate carrier mothers (41%) although this was not significant. The potential use of these prospective data on the fra(X) syndrome is emphasized.

Guidelines for the preparation and analysis of the fragile X chromosome in lymphocytes.

The following guidelines were adopted by an Ad Hoc Committee convened at the Fourth International Workshop on the Fragile X Syndrome and X-Linked Mental Retardation to establish minimum cytogenetic standards for the preparation and analysis of the fragile X chromosome. The intention of the committee was to develop and provide practical standards for the routine cytogenetic detection of the fragile X. The guidelines describe reasonable criteria for effective tissue culture methods for eliciting the Xq27.3 fragile site in vitro and for the analysis of such chromosome preparations.

Benign ovarian teratomas. An analysis of their cellular origin.

To determine the cellular origin of benign ovarian teratomas with a 46,XX chromosome constitution, DNA markers recognizing restriction fragment length polymorphisms (RFLPs) were hybridized to DNA from six teratomas and their hosts. DNA markers heterozygous in the host were completely heterozygous in two of the teratomas. The remaining four showed a mixture of homozygosity and heterozygosity. These results suggests that most of the analyzed benign ovarian teratomas arose from germ cells after the first meiotic division by failure of meiosis II. Teratomas heterozygous for all tested markers may arise from failure of meiosis I. In addition, 21 cases were karyotyped and analyzed for centromeric chromosome markers to study the mechanism by which they were generated. Three of these tumors were homozygous when the host was heterozygous and therefore resulted from a failure of meiosis II or duplication of a mature ovum. Three cases were heterozygous for the centromeric chromosomal marker like the host and therefore probably originate from a premeiotic cell or a cell in which meiosis I has failed. One ovarian teratoma had an aberrant karyotype 47,XX,+8.

Autosomal dominant cerebellar ataxia deafness and narcolepsy.

A new autosomal dominant syndrome in a Swedish pedigree is described. Five patients were affected with cerebellar ataxia and sensorineural deafness. Four of these patients had symptoms of narcolepsy. Optic atrophy, other neurological abnormalities and psychiatric symptoms developed with increasing disease duration. Three patients had non-neurological disease in addition, including diabetes mellitus in two and hypertrophic cardiomyopathy in one. Autopsy with neuropathological examination was performed in one case. Molecular studies focused on the short arm of chromosome 6, including the HLA DR2 locus associated with narcolepsy and the (CAG)n repeat at the spinocerebellar ataxia type 1 (SCA1) locus. Biochemical investigation of muscle biopsy of one case indicated mitochondrial dysfunction with selective decrease in ATP production for substrates that normally give the highest rates. The activity of glutamate dehydrogenase was reduced, indicating a low mitochondrial density. We postulate an autosomal dominant genetic factor responsible for this syndrome. Linkage was excluded to HLA DR2, and a normal sized SCA1 repeat was observed. We conclude that a locus predisposing to ataxia, deafness and narcolepsy exists outside this region of chromosome 6.

A trial of selenium and vitamin E in boys with muscular dystrophy.

The administration of selenium and vitamin E was tried in a group of 20 boys with muscular dystrophy. Muscular strength was measured at intervals of 6 months. The boys were treated for 1 year (selenium 6 micrograms/kg for 6 months and 20 micrograms/kg for 6 months), followed by 1 year of no treatment. The whole series was completed in 16 boys, nine of whom had classical Duchenne muscular dystrophy and the rest who had more benign variants. No boy showed any side effects. The decrease of muscle strength was slightly more rapid during the second year (no treatment) than during the first year (with treatment) of the trial. The difference was, however, slight and could conceivably be explained by the increase of age. No boy showed any practically usable increase of muscle strength during the year of treatment. The minimal muscle strength required for walking is presented.

Hyperkalemic periodic paralysis caused by recurring mutation in the adult muscle sodium channel alpha-subunit gene.

Linkage studies and mutation analysis were performed in two Swedish families with hyperkalemic periodic paralysis (HYPP), an autosomal dominant inherited disorder characterized by episodic muscle weakness associated with increasing or high levels of serum potassium. The gene for HYPP is the gene encoding the alpha-subunit of the sodium channel of adult human skeletal muscle (SCN4A). SCN4A has been localized on chromosome 17 q closely linked to the human growth hormone gene. Linkage between a microsatellite polymorphism in the SCN4A gene and the disease was shown in two Swedish families (Z = 12.10 theta = 0). Sequence analysis revealed that the two Swedish families have got a C to T transition at position 2188 in the cDNA. At the protein level this Thr 704 to Met mutation is located in the fifth membrane spanning segment of domain II of the protein, as previously described (28). The mutation was linked to different microsatellite alleles regarding both a (GT)n and a (GA)n repeat in the gene. Either the families are related and new mutations have occurred in both microsatellites when the pedigrees were separated or the mutation has arisen independently in the two families analysed. From the mutant alleles characterized so far it seems as if a limited number of mutations is present in this gene.

Familial ovarian dermoid cysts.

A family consisting of a mother and her two daughters with ovarian dermoid cysts showed an increased frequency of aneuploidy and chromosomal breakage indicating chromosomal instability.