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A major advance in the molecular diagnosis of facioscapulohumeral muscular dystrophy is the recently reported elimination of confounding DNA fragments arising from homologous sequences located at 10q26. In order to evaluate the specificity and sensitivity of this important diagnostic test, we have compared a group of 130 patients fulfilling the diagnostic criteria for FSHD with 200 control subjects not known to have an increased risk of having an FSHD mutation. Among the FSHD cases the smallest BlnI/EcoRI fragment sizes ranged from 10 to > 48 kb with 94.6% (95% CI 89.2-97.8%) of cases having fragment sizes of 34 kb or less. Among the 400 chromosomes from controls the smallest BlnI/EcoRI fragment observed with the EcoRI/BlnI double restriction enzyme digest was 38 kb +/- 2 kb, suggesting a test specificity at a fragment size < 34 kb of or very near to 100% (lower 95% CI 98.2%). Test sensitivity at < 34 kb is estimated at 94.6% (95% CI 89.2-97.8%), all outliers having fragments > 38 kb. The Southern blot analysis with DNA probe p13E-11 has created a valuable molecular diagnostic test for FSHD.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal-dominant disorder which has been mapped to the 4q35 region. In order to saturate this distal 4q region with DNA markers, a laser-based chromosomal microdissection and microcloning procedure was used to construct a genomic library from the distal 20% of chromosome 4, derived from a single human metaphase spread. Of the 100 microclones analyzed from this library, 94 clones contained inserts sized from 80-800 bp, with an average size of 340 bp. Less than 20% of these clones hybridized to human repeat sequences. Seventy-two single-copy clones were further characterized by Southern blot hybridization against a DNA panel of somatic cell hybrids, containing various regions of chromosome 4. Forty-two clones mapped to chromosome 4, of which 8 clones mapped into the relevant 4q35 region. Twenty of these chromosome 4-specific clones were screened against "zoo-blots"; 11 clones, of which 3 mapped to 4q35, identified conserved sequences. This is the first report to describe the isolation of potential expressed sequences derived from the FSHD region. These chromosome region-specific microclones will be useful in the construction of the physical map of the region, the positional cloning of potential disease-associated genes, and the identification of additional polymorphic markers from within the distal 4q region.

In facioscapulohumeral muscular dystrophy (FSHD), the wide range of clinical severity observed both within and between families has obscured past attempts to identify any phenotypic differences between families from which phenotype-genotype correlation could proposed, although it is noted that age at onset is youngest and severity greatest in isolated cases. From 14/16 large 4q35-linked FSHD families, and 25/34 isolated cases exhibiting a de novo D4F104S1 DNA fragment, we find a significant correlation between proband age at onset and FSHD-associated D4F104S1 fragment size (r = 0.56; p < 0.001), with the smallest fragments occurring in isolated cases. A similar correlation (r = 0.70; p < 0.01) with fragment size is observed for age to loss of ambulation in 16 subjects using a wheelchair. We find also that age at onset appears younger with successive generations in the 4q35 families. We propose that fragment size at D4F104S1, together with a possible generational effect, accounts for a significant part of the wide phenotypic variation in FSHD. Our results predict a more limited range for severity within families, and in one family with a 4q35-linked 38kb fragment support scapulohumeral presentation without facial involvement as a late onset variant of FSHD. We propose that in FSHD, quantitative variation in a uniform mutation mechanism influences age at onset, but by deletion rather than expansion of DNA.

Facioscapulohumeral dystrophy (FSHD) is an autosomal-dominant neuromuscular disorder with a prevalence of 1 in 20,000. The DNA marker p13E-11 (D4F104S1) detects a de novo DNA rearrangement in the majority of sporadic and FSHD cases. These rearrangements consist of deletions of multiple copies of tandem repeat (D4Z4). We have studied 34 new mutation FSHD families of which 26 showed a de novo fragment with p13E-11. In three of the remaining eight families without a de novo fragment, germinal mosaicism was noted. In each case, the proband had inherited a small EcoR1 fragment from the clinically unaffected mother; however, the hybridization signal intensity of this fragment in the mother's DNA was significantly reduced in all three families. This is the first study to describe such mosaicism in FSHD families using DNA analysis and therefore has a considerable significance for genetic counseling and prenatal diagnosis.

The wide range of severity in facioscapulohumeral muscular dystrophy (FSHD) complicates genetic advice, although onset age is youngest and severity is greatest in isolated cases. From 14 of 16 large FSHD families which are 4q35 linked, and from 25 of 34 isolated cases exhibiting a de novo D4F104S1 DNA fragment, we find a correlation between proband age at onset and FSHD-associated D4F104S1 fragment size (r = 0.56; P < 0.001), with the smallest fragments occurring in isolated cases. A 4q35-linked 38-kb fragment in one family supports scapulohumeral presentation without facial involvement as a milder late-onset variant of FSHD, and with apparent "unaffected" recombinants in small families, suggests that nonpenetrance is more likely with large fragment sizes. Our results, predicting a more limited range for severity within families, and suggesting > 85% of FSHD maps to 4q35, will facilitate genetic counseling. We propose that quantitative variation in a uniform mutation mechanism influences age at onset, but by deletion rather than expansion of DNA.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant condition with variable age of onset and severity. Identification of a de novo DNA fragment by probe p13E-11 (D4F104S1) established the diagnosis of new mutation FSHD in 27 of 31 sporadic cases. The clinical data for these certain new mutation cases were as follows: 13 boys, 14 girls; mean age of onset 6.8 years; significant leg weakness in 19/27 (70%) (8/27 (30%) used wheelchairs at a mean age of 17.7 years); high tone sensorineural deafness in 10/27; visual acuity and direct ophthalmoscopy were normal. Congenital facial diplegia and sensorineural deafness in three children suggest that infantile FSHD is not a genetically separate disorder from FSHD. Ascertainment bias may explain the difference in severity between this group and typical familial cases. Molecular analysis for FSHD should be considered in children with either congenital or early onset facial weakness or diplegia.

Four DNA markers on the distal long arm of chromosome 4 have been analyzed for their linkage relationship to facioscapulohumeral muscular dystrophy (FSHD) in a series of 23 families with this disease. Two hypervariable markers, pH30 (D4S139) and EFD 139.1 (D4S184), both show close linkage with the disorder, with a maximum recombination fraction (theta max) of .02 and a maximum lod score (Zmax) of 36.77 and 34.50, respectively; two other markers, the locus for factor XI (F11) and the microsatellite marker Mfd22 (D4S171), both show less close linkage, with respective theta max of .16 (Zmax = 3.40) for F11 and .24 (Zmax = 1.61) for D4S171. While the relative ordering and orientation of the loci on the chromosome remain provisional, analysis of 15 individual recombination events in seven families supports the order D4S171-F11-D4S184-D4S139-FSHD, with the disease locus telomeric to all four markers.

Close linkage of a hypervariable DNA probe on chromosome 4q (pH30, locus D4S139) has been found with the locus for facioscapulohumeral disease. Three recombinants were identified in a total of 140 meioses, giving a maximum lod score of 36.77 at a recombination fraction of 0.02. All but two of the families studied proved informative with this probe; all informative families showed evidence of linkage (except one family with a single scorable meiosis), making genetic heterogeneity unlikely from our data. The close linkage and highly informative nature of the probe will make it suitable for clinical application in presymptomatic and prenatal diagnosis. We have also confirmed loose linkage with the marker (Mfd22, locus D4S171) used to establish the initial assignment of the disorder to chromosome 4.

Clinical data are presented from a survey of 41 families with dominantly inherited facioscapulohumeral muscular dystrophy (FSHD) in which over 500 family members were examined, including 168 affected subjects. New mutation could account for six isolated cases. Results suggest that 33% of heterozygotes over 40 years are mildly affected and a majority develop significant lower limb weakness; 19% over 40 years require wheelchairs. Presymptomatic testing of serum creatine kinase level (CK) is limited as a raised level occurs in only 80% of affected males under 40 years and 48% of affected women. Distribution of weakness, severity, age at onset, and CK varied between subjects, but provided no clinical evidence for genetic heterogeneity in a comparison between the 11 largest families. The conclusion of genetic homogeneity in FSHD, including subjects previously diagnosed as FSH type spinal muscular atrophy, is strongly supported by recent genetic linkage data.

Thirty-three young boys (mean age 3.42 years) with Duchenne muscular dystrophy (DMD) and 21 normal control boys (mean age 3.51 years) were studied prospectively to determine whether it is possible to objectively assess locomotor function in young boys with DMD so that they can be included in treatment trials. An initial reproducibility study using a hand-held myometer demonstrated that this method was not useful. The Hammersmith Motor Ability Score demonstrated an increase in developmental abilities with age which was markedly different from normal. The locomotor quotient of the Griffiths' Scales demonstrated a deterioration of quotient scores and is a useful method of assessment that could be used in treatment trials involving young boys with DMD. Sample size planning for treatment trials is discussed.

Emery-Dreifuss muscular dystrophy (EDMD) is an X-linked humeroperoneal dystrophy associated with cardiomyopathy that is distinct from the Duchenne and Becker forms of X-linked muscular dystrophy. Linkage analysis has assigned EDMD to the terminal region of the human X chromosome long arm. We report here further linkage analysis in two multigenerational EDMD families using seven Xq28 marker loci. Cumulative lod scores suggest that EDMD is approximately 2 cM from DXS52 (lod = 15.67) and very close to the factor VIII (F8C) and the red/green color pigment (R/GCP) loci, with respective lod scores of 9.62 and 10.77, without a single recombinant. Several recombinations between EDMD and three proximal Xq28 markers suggest that the EDMD gene is located in distal Xq28. Multipoint linkage analysis indicates that the odds are 2,000:1 that EDMD lies distal to DXS305. These data substantially refine the ability to perform accurate carrier detection, prenatal diagnosis, and the presymptomatic diagnosis of at-risk males for EDMD by linkage analysis. The positioning of the EDMD locus close to the loci for F8C and R/GCP will assist in future efforts to identify and isolate the disease gene.

Thirty-three boys with Duchenne muscular dystrophy (DMD) and a mean age of 3.4 years were assessed with the Griffiths Developmental Scales, the Reynell Language Scales and the British Picture Vocabulary Scales at six-monthly intervals over a one-year period. The boys showed developmental delay, which was most severe in the locomotor and language areas. The locomotor quotients deteriorated over time, but the other quotients did not. Maternal intelligence, home environment and social class had little effect on the aetiology of the developmental delay, and the behavioural problems seen in young boys with DMD may be secondary to it.

DNA from 164 unrelated Duchenne muscular dystrophy patients was screened with cDNA probes from the dystrophin gene. Molecular deletions were demonstrated in 82 (50%) subjects. Sixty-two deletions (76%) were detected using cDNA probes Cf56a (cDNA 8) and Cf56b (cDNA 6-7) which map to the centre of the gene, while 22 deletions (27%) mapped to the 5' end of the gene. In three subjects, the deletion extended from the 5' end to the centre of the gene. One deletion was identified by probe 47-4 (cDNA 5b-7) alone. In six of the deletions, junction fragments of altered size were observed. Using the three cDNA probes, RW2kb, Cf56a (cDNA 8) and Cf56b (cDNA 6-7), 99% of the deletions were detected. This will have implications for prenatal diagnosis in deletion families. Unlike Becker muscular dystrophy, where the deletions are more homogeneous, the deletions in the present study were heterogeneous both in size and position. No correlation between intelligence and either site or extent of deletion was found.

Molecular deletion screening with cDNA probes from the dystrophin gene was undertaken in patients with Becker muscular dystrophy from 58 separate families. Deletions were found in 41 (71%) of these families. Thirty-four (83%) of the deletions started in the same intron near the centre of the gene, and although there was no precise correlation between clinical severity and deletion pattern, the commonest deletion pattern, which was present in 49% of all deletion families, is associated with a mild phenotype.

The existence of linkage has been investigated between the Xg blood group system, two DNA restriction fragment length polymorphisms (RFLPs) located on the short arm of the X chromosome, Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). No linkage was found between the Xg locus and the more proximal RFLP (L 1.28); close linkage between Xg and the more distal RFLP (lambda RC8) was also excluded. Both RFLPs show linkage with DMD but are not closely linked with each other. Analyses of 11 families with DMD and ten with BMD, informative for the Xg blood group, reinforce the conclusions of others that there is no measurable linkage between the loci for Xg and for the X-linked forms of muscular dystrophy.

Myotonic muscular dystrophy is an inherited disorder affecting many organs, though the underlying biochemical defect is unknown. A recent publication [1] suggested that the metabolic lesion may be associated with defective phospholipid metabolism. These workers observed impaired calcium-stimulated phosphatidic acid accumulation in red cell ghosts from individuals with myotonic dystrophy compared with normal controls. The present study investigated some points of calcium-activated phosphatidylinositol metabolism in red cell ghosts from patients with myotonic dystrophy, those at risk of developing the disease and normal individuals. No differences between the three groups could be found in the incorporation of 32P into endogenous phosphatidylinositol nor in the distribution of label between the various phosphatidylinositols. Additionally, no differences were observed in either basal or calcium-activated phosphatidylinositol phosphate breakdown by phosphodiesterase. This would suggest that the observed decreased phosphatidate accumulation [1] may be due to impaired diacylglycerol kinase activity.

A total of 33 young boys (mean age 3.4 years) with Duchenne muscular dystrophy and 21 normal controls (mean age 3.5 years) were assessed using the Griffiths's mental development scales and the Reynell language scales. The boys with Duchenne muscular dystrophy were significantly developmentally delayed when compared with the control group. The developmental delay was most pronounced in locomotor function and language. There was no significant difference in social class distribution. Early diagnosis of Duchenne muscular dystrophy is of vital importance if secondary cases within families are to be prevented. While diagnosis is still unacceptably late in most cases, it can be improved if all boys with this pattern of developmental delay are screened for Duchenne muscular dystrophy by measurement of creatine kinase activity.

In any family study using information gathered retrospectively, the influence of the method of ascertainment on the observed segregation ratio in sibships needs careful consideration. The study of kindred members from outside the area of primary ascertainment is invaluable in providing segregation data with minimal ascertainment bias. For facioscapulohumeral muscular dystrophy (FSHD), using this approach, and based on the presence or absence of characteristic clinical signs rather than on an historical account of age at onset, estimates were derived for penetrance of the FSHD gene of less than 5% for ages 0 to 4 years, 21% for ages 5 to 9, 58% for ages 10 to 14, 86% for ages 15 to 19, and 95% penetrance for age 20 years and over. No difference between families was identified. These figures should facilitate genetic counselling and the interpretation of genetic linkage study results in FSHD.

A register of families with Duchenne muscular dystrophy (DMD) has been maintained in Wales since 1973. Since 1986 we have attempted to refine carrier status, and when necessary offer prenatal diagnosis, for those at significant risk by using intragenic probes. cDNA probes were included from the beginning of 1988. Thirty-four (30%) of the 115 women tested were assigned a risk of carrying the DMD gene of less than 5%. Thirty-three (29%) of the women at 5% or greater risk are now able to have prenatal diagnosis using a molecular deletion; such deletions were detected in 50% of affected boys. The remaining women could have prenatal diagnosis using a linked intragenic probe with an error rate varying between 0.25% and 9%. In 19 cases DNA samples from DMD boys who were dead at the time of analysis were used, indicating that it is essential to bank DNA from all males affected by DMD. We conclude that a large proportion of women at risk of carrying the DMD gene can now be helped by DNA studies.

New molecular developments in our understanding of Duchenne and Becker muscular dystrophies are affecting the practical approach to genetic counseling, carrier detection, and prenatal prediction for these disorders. A plan of an investigation combining DNA and conventional techniques is outlined that is suitable for centers not actively engaged in molecular genetics research, based on the detection of molecular deletions, the most efficient use of multiple DNA polymorphisms, and the integration of this data with creatine kinase and pedigree information. Such an approach now allows accurate carrier detection for most women at risk as well as an acceptable degree of accuracy in prenatal detection for a proportion of carrier women.

Seventy three sisters of boys with Duchenne muscular dystrophy and their families were studied using up to seven deoxyribonucleic acid (DNA) probes linked to the gene on the short arm of the X chromosome. Fifty three (73%) were informative for flanking markers, a further 18 (24%) being informative for a single marker only. Predictions based on pedigree structure and creatine kinase information from the individuals and their female relatives gave more than half (55%) of the sisters a risk for being a carrier of below 10% or above 90%. The addition of information derived from the inheritance of flanking DNA markers, where they exist, improves the situation so that many more sisters (77%) can be allocated into either high or low risk categories.

The inheritance of a restriction fragment length polymorphism (RFLP) detected by a cloned DNA sequence (p754) from the short arm of the X chromosome has been studied in 14 Duchenne muscular dystrophy kindreds and six Becker muscular dystrophy kindreds. The linkage data obtained suggest that both the DMD and BMD loci are located in the same region (p21) on the short arm of the X chromosome at a distance of about 15 to 20 cM from the 754 locus. Data from families informative for both the p754 and L1.28 polymorphisms suggest that p754 is closer to the disease loci than is L1.28.

A panel of 399 individuals from 24 kindreds with facioscapulohumeral muscular dystrophy (FSHD) has been established for genetic linkage studies. A previous suggestion of linkage on the distal long arm of chromosome 14 to the locus (IGHG) for the constant region of the heavy chain of IgG immunoglobulin was tested from serum Gm allotypes and from DNA analysis using an IGHG DNA probe. After applying an age-dependent weighting for presently unaffected but at risk individuals close linkage between the IGHG and FSHD loci was excluded.

A linkage study using two different restriction fragment length polymorphisms (RFLPs) identified with cloned DNA sequences has failed to provide evidence for genetic heterogeneity in Duchenne muscular dystrophy (DMD) when tested against intelligence quotient (IQ). Analysis of data for age of confinement to a wheelchair against IQ gave no evidence for heterogeneity. These results are of a practical as well as theoretical significance, since the existence of multiple loci causing DMD would make it more difficult to apply linkage data to genotype prediction in this disease.

The inheritance of seven restriction fragment length polymorphisms detected by DNA probes has been studied in families with Duchenne and Becker muscular dystrophies (DMD and BMD). The probes used have all been mapped to the short arm of the X-chromosome, four being distal and three proximal to the disease loci located within the Xp21 region. Linkage analysis of the DNA polymorphisms in relation to the two disorders showed similar genetic distances. Data obtained from DMD and BMD families have been combined to give more precise values for the different recombination fractions. Combined use of these polymorphic DNA markers will be of practical value in the genetic counselling of women at risk for Duchenne and Becker muscular dystrophy.

Duchenne muscular dystrophy (DMD) and its less severe form Becker muscular dystrophy (BMD) are allelic disorders. It has been suggested that in the mutations involving BMD, the translational reading frame of messenger RNA is maintained and a smaller, though partially functional, protein is produced. In order to test this, the exon-intron boundaries of the first ten exons of the DMD gene were determined, and 29 patients were analyzed. In a number of BMD patients (mild and severe BMD), the reading frame of messenger RNA was not maintained. On the basis of these findings, a model for reinitiation from an internal start codon is suggested.

A programme was introduced in Wales to screen all 18 month old boys who were not yet walking for raised creatine kinase activity within the existing community developmental screening programme. During an 18 month period 25 229 such boys were identified of whom 19 930 (79%) had a Denver developmental screening test and 338 (1.7%) of these were not walking. Two hundred and five of those who did not walk (61%) had creatine kinase activity assayed and two cases of Duchenne muscular dystrophy were detected. We conclude that screening boys of 18 months who do not walk is worthwhile if the opportunity arises, but that a population based screening programme of this type is not justified as detection rates will be unacceptably low.

The inheritance of two restriction fragment length polymorphisms (RFLPs) on the short arm of the human X chromosome has been studied relative to Duchenne muscular dystrophy. This provides a partial genetic map of the short arm of the human X chromosome between Xp110 and Xp223. The data were derived from the segregation between a RFLP located at Xp21-Xp223, the DMD locus, and a RFLP located at Xp110-Xp113. The genetic distance from Xp110 to Xp223 was found to be approximately 40 centimorgans (cM). This provides experimental confirmation that 1cM corresponds to approximately 1,000 kilobase pairs of DNA for this region of the human X chromosome. Our data confirm that the DMD mutation lies between Xp223 and Xp110. The availability of flanking probes surrounding the DMD locus will assist in the ordering of further DNA sequences relative to the mutation.

Deletions in the gene sequence for Duchenne (DMD) and Becker (BMD) muscular dystrophy were detected in affected males with four cDNA probes, Cf56a, Cf23a, Ca1A, and Cf27. Most of the deletions were seen with only one of the probes. Cf23a detected all BMD deletions seen with Cf56a and some that were not. The same markers also detected restriction fragment length polymorphisms for those cases where deletions were not evident. The probes were also used successfully for prenatal diagnosis in two families each with two DMD affected males. In DMD families successive application of probes Cf56a, Ca1A, and Cf27 will give a 70% chance of detecting the mutation. BMD families should first be screened with the Cf23a probe.

A linkage study in 30 Becker muscular dystrophy (BMD) kindreds using three cloned DNA sequences from the X chromosome which demonstrate restriction fragment length polymorphisms (RFLPs), suggests that the BMD gene is located on the short arm of the X chromosome, in the p21 region. The genes for Becker and Duchenne dystrophies must therefore be closely linked, if not allelic, and any future DNA probes found to be of practical use in one disorder should be equally applicable to the other. The linkage analysis also provides data on the frequency of recombination along the short arm of the X chromosome, and across the centromeric region.

Serum creatine kinase levels in 39 control females and 59 obligate carriers of Becker muscular dystrophy (BMD) have been used to construct likelihood ratios for carrier detection. In 24 possible carriers of BMD, analysis of DNA with X chromosome specific DNA probes linked to the dystrophy gene, has been used in conjunction with creatine kinase measurement to calculate final risk estimates of carrier status. Incorporation of information from probe genotype into the Bayesian calculation, enables a substantially lower risk to be deliniated for some possible carriers of the BMD gene. Thus, although the existing DNA probes are not sufficiently closely linked to BMD to be used in prenatal diagnosis, they can make a major contribution to genetic counseling by refining the estimated probability of carrier status.

Two DNA restriction fragment length polymorphisms show genetic linkage to the Duchenne muscular dystrophy locus on the short arm of the X chromosome. Examples are given of families in which these polymorphisms can be used in the prediction of genotype for this disorder.

The mean levels of serum creatinine phosphokinase (CPK) were studied in three groups of women: normal controls (57), obligate carriers for Duchenne muscular dystrophy (30), and mothers of isolated cases of this disease (35). The distribution of the levels in these groups was significantly different and was in keeping with the hypothesis that one-third of isolated cases result from new mutations. The control and carrier ranges overlapped considerably, with the level of CPK of 33% of obligate carriers coming within the 97 1/2 centile of the normal range. Odds against an individual being a carrier were derived for specific mean values of CPK. They should be considered with genetic information using Bayes's theorem. The mean CPK levels in obligate carriers showed significant familial clustering. This may have implications in carrier detection.

A study of DNA restriction fragment polymorphisms and Becker muscular dystrophy has shown eight families informative for the cloned sequence L1.28, which is located on the short arm of the X chromosome between Xp110 and Xp113. Analysis of these families reveals linkage between the two loci, with the maximum likelihood estimate of the genetic distance being 16 centiMorgans (95% confidence limits between 7 and 32 centiMorgans). Since a study of DNA polymorphisms in Duchenne muscular dystrophy has shown a comparable linkage distance with L1.28, our results suggest that the locus for Becker muscular dystrophy, like that for Duchenne dystrophy, is on the short arm of the X chromosome, and further that these two loci may be closely linked or possibly allelic.

A syndrome of Duchenne muscular dystrophy (DMD), adrenal hypoplasia, glycerol kinase deficiency, and mental retardation has been recognised. We report a further case ascertained from a history of DMD, severe mental retardation, and an Addison-like disorder. Cytogenetic analysis of the proband revealed an interstitial deletion of the short arm of the X chromosome. from Xp21.1 to Xp22.11, comprising about 9% of the length of the normal X chromosome. His mother was heterozygous for the deletion, but his maternal grandmother and sister both had two normal X chromosomes. DNA probe analysis confirmed the existence of a deletion in the affected boy, as probes 754, C7, XJ1-1, and pERT87 consistently failed to hybridize to his DNA. His sister was heterozygous for the RFLP associated with 754, thus confirming that she had two normal X chromosomes. There was no evidence of chronic granulomatous disease, other immunological defect, or retinitis pigmentosa in this case. Biochemical studies revealed gross glyceroluria and hyperglycerolaemia, indicating glycerol kinase deficiency which has been confirmed enzymatically. We have subsequently screened 21 other boys with DMD for glyceroluria and found one other case. Cytogenetic analysis has also been performed in nine other families, where a boy with DMD has been shown to have a deletion of DNA sequences localised to the region Xp21. None of these cases demonstrated any cytogenetic abnormality, nor has their clinical course been unusual.