Clinical Genetics 1989: 36: 31-37

A survey of manifesting carriers of Duchenne and Becker muscular

dystrophy in Wales ANDREW NORMAN AND PETER HARPER

Institute of Medical Genetics, University Hospital of .Wales, Heath Park, Cardiff, UK

Manifesting carriers of Duchenne and Becker muscular dystrophy are uncommon but well described. Such patients are of particular importance with regard to the differential diagnosis from autosomal recessive limb-girdle muscular dystrophy. All mothers of affected males known to the Genetic Register of Muscular Dystrophy Families in Wales were contacted, and 167 out of a possible 190 were examined. It was estimated from pedigree and creatine kinase analysis that 119 out of the 167 were carriers of the Duchenne/Becker gene. Three manifesting camers were identified, giving the proportion affected as 3/119=2.5%. We estimate the prevalence of manifesting carriers to be 1 in 1oOOOO of the female population, a figure comparable to the prevalence of autosomal recessive limb-girdle muscular dystrophy. During the period of the survey, several other women with similar clinical findings but without an appropriate family history were seen. We strongly suspect that some of these are also manifesting carriers of the Duchmne/Becker gene.

Received 20 January, accepted for publication 11 February 1989

Key wor& Becker muscular dystrophy; Duchenne muscular dystrophy; manifesting camers

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are alle- lic X-linked diseases with similar clinical features (Kingston et al. 1984). BMD is characterised by later onset and slower pro- gression (Bccker & Kiener 1955). Manifes- ting camers of DMD are uncommon, but well documented (Kryschowa & Abowjan 1934, Moser & Emery 1974). Manifesting carriers of BMD are less commonly de- scribed (Aguilar et al. 1978). Such patients are of particular importance with regard to the differential diagnosis from autosomal recessive limb-girdle dystrophy (LGD) in the isolated adult female patient (Moser & Emery 1974, Emery & Walton 1967). Differ-

ential diagnosis between BMD and LGD is also diffkult in the isolated adult male patient, though this has been clarified re- cently by the use of molecular techniques (Norman et al. 1989).

We are not aware of any systematic sur- vey of manifesting carriers since that of Moser & Emery (1974), who attempted to estimate prevalence. A register has been kept of all females known to be at risk of carrying the DMD or the BMD gene in Wales for the past 15 years. We undertook a survey to discover how many of these women had clinical signs of muscle weak- ness on physical examination. Several other women with similar signs, but no family

32 N O R M A N A N D H A R P E R

history were referred to us during this pe- riod; we strongly suspect that they also are manifesting the DMD or BMD gene.

Material and Methods

An attempt was made to contact all mothers of sufferers of DMD and BMD known to the Wales register, by sending a letter to each woman's last known address asking if she would be willing to participate in a clin- ical survey. Muscle strength was assessed by manual muscle testing, by AN using the MRC scale, in the women's own homes or at a hospital clinic, as appropriate.

Out of 190 women, 151 agreed to be tested and an additional 16 women in these families were examined, giving a total num- ber of 167. All women had blood taken for creatine b a s e (CK) analysis on three occasions. This was combined with pedigree analysis to assign a risk of carrying the DMD or BMD gene to non-obligate car- riers after the method of Sibert et al. (1979) and Kingston et al. (1985) respectively. The number of carriers in this group was in- ferred from the sum of their individual risks. DNA analysis, using linked restriction frag- ment length polymorphisms, was also per- formed in many cases. This substantially altered the risk for only a few women and, as would be expected, made no difference to the group risk.

Some deceased manifesting carriers were reported to us. We omitted such cases be- cause of the impossibility of adequate as- sessment, and because their inclusion would be inappropriate in a survey intended to estimate prevalence.

Results

One hundred and sixty-seven women were examined: 49 were obligate carriers of DMD and 85 were mothers of isolated cases of DMD. There were 10 obligate carrier

mothers of men with BMD, 7 daughters of men with B M D and 7 mothers of isolated cases. Nine women fell into none of these categories.

Table 1 shows the mean ages, mean CK values and sums of risks for each of these groups.

In total 66 women were obligate carriers and 101 were possibIe carriers. Summing the risks of each of these 101 women allowed us to estimate that we would expect a total of 53 carriers in this group. The predicted total number of carriers examined was therefore 119 (Table 1).

The survey identified two manifesting carriers of Duchenne muscular dystrophy and one manifesting carrier of Becker mus- cular dystrophy. Each is discussed in detail below, and in Table 2. The proportion of carriers of DMD and BMD who manifest muscle weakness is 311 19 = 2.5%.

Case Reports

Case 1 This 45-year-old lady is an obligate carrier of DMD. She had one brother with DMD, who died at 13, and one son who died at 17 from the same condition. She first noted weakness of the left arm at 28 years; the strength of her arm deteriorated slowly and it became wasted. She experienced great dif- ficulty in doing up buttons and unscrewing jars. Initially there was no weakness of the lower limbs, but by the age of 37 she was having some difficulty climbing stairs and inclines. On examination it was immediately noticeable that she used trick movements of the left ann to overcome weakness of elbow flexion. There was wasting of the small muscles of the left hand. She had mild proximal muscle weakness of both lower limbs, but could walk on the flat unaided. Permission for muscle biopsy was refused.

M A N I F E S T I N G C A R R I E R S 33

Table 1

Mean ages, mean creatine kinase (CK) values, sums of risks and number of carriers by group,

Mean age Mean CK (SD) (W Sum of Number of

(years) (lull) risks carriers

DMD obligate carriers (n=49) DMD mothers of isolated cases (n = 85)

BMD obligate carrier daughters (n=7)

44.0 (11.7) 41.3 (10.7)

26.1 (8.4) BMD obligate carrier mothers (n= 10) 48.2 (9.1)

BMD mothers of isolated cases (n = 7) 49.9 (9.5) Others (n=9) 34.0 (12.0)

Total predicted number of carriers

361 (452) 49 49 197 (215) 46.3 46 198 (168) 10 10 142 (59) 7 7 106 (59) 3.3 3 460 (708) 3.9 4

119

Case 2 This 51-year-old lady is an obligate carrier of DMD. She had an affected brother, who died at 21, and two affected sons who died at 21 and 18. She had complained of weak- ness of the legs since the age of 40, and this caused increasing difficulty climbing stairs and inclines by the time she was 43. She can now walk approximateiy 100 yards on the flat, with the aid of a stick. On examination there was moderately severe weakness of the pelvic girdle muscles, leading to Gower’s manoeuvre, but no demonstrable weakness of the upper limb girdle at all. Muscle bi- opsy was consistent with Duchenne muscu- lar dystrophy.

Case 3 This 55-year-old lady has three younger brothers with BMD, two of whom require wheelchairs for mobility and cannot stand unaided. She had CK values four times greater than the upper limit of normal at 42, giving her a risk of carrying the gene of more than 99.9%. She has experienced increasing difficulty walking up stairs for the past 10 years, and more recently has had difficulty rising from chairs. On exam- ination there was moderate weakness of the pelvic girdle, more marked on the right. There was no weakness of the distal lower limb muscle, nor of the upper limbs. Muscle biopsy was consistent with BMD.

During the period of this study we saw several other women with symptoms and signs similar to those in the cases reported above, but in whom family history was negative.

Cases 4 and 5 The elder of a pair of monozygotic twin girls, now aged 48, complained of difficulty in rising from chairs and climbing stairs; these symptoms had been present for at least 6 years and were very gradual in their onset. She had never been able to run prop- erly, and was “the least athletic girl in the class at school”. Examination of the upper limbs was entirely normal. There was mod- erate weakness, but no wasting of the pelvic girdle muscles, and she needed the support of her arms to rise from sitting. Calf hy- pertrophy was present and the CK was 1990 id-’. Muscle biopsy showed variation in fibre size and an increase in intermyseal connective tissue, features consistent with DMD (Fig. 1).

The younger twin denied any muscle weakness, but had mild proximal muscle weakness confined to the hip flexors and extensors only. She did not have calf hy- pertrophy, and her CK was 1420 iu1-l. Her muscle biopsy showed changes similar to, but less florid than, those of her sister. They were the only children of unrelated parents

Table

2

Clin

ical

find

ings

and

cre

atin

e ki

nase

val

ues

in m

anife

stin

g ca

rrie

rs o

f Duc

henn

e an

d B

ecke

r m

uscu

lar

dyst

roph

y. N

umbe

rs in

col

umn

6 r

efer

to

the

MR

C m

uscl

e st

reng

th s

core

- 5

norm

al p

ower

, 4

mov

emen

t ag

ains

t re

sist

ance

, 3

mov

emen

t ag

ains

t gr

avity

, bu

t no

t re

sist

ance

, 2

mov

emen

t w

ith g

ravi

ty e

limin

ated

.

Age

at

Age

at

Cre

atin

e C

alf s

ize

Pat

ient

C

arrie

r on

set

Pre

dom

inan

t ex

amin

atio

n ki

nase

an

d nu

mbe

r ris

k (y

ears

) sy

mpt

om

(yea

rs)

Pat

tern

of

mus

cle

wea

knes

s W

i)

Sym

met

ry

W

P

1 2

Obl

igat

e 28

W

eakn

ess

left

45

Nec

k ex

tens

ion

Duc

henn

e ar

m a

nd h

and

Upp

er a

rm fl

exio

n,

exte

nsio

n. r

otat

ion

Len

elbo

w fl

exio

n Le

n el

bow

ext

ensi

on

Left

wris

t mov

emen

ts

Len

finge

r m

ovem

ents

H

ip m

ovem

ents

Obl

igat

e 40

Wea

knes

s of

51

U

pper

lim

bs

Duc

henn

e le

gs

Hip

ext

ensi

on, f

lexi

on a

bduc

tion

3 99

.9%

45

Wea

knes

s of

55

U

pper

ilm

bs

Bec

ker

legs

H

ip fl

exio

n H

ip e

xten

sion

4 28

00

Nor

mal

4 2 4 4 4 4 5 11

95

Sym

met

rical

5 93

7 H

yper

troph

y 4

mor

e m

arke

d 4

on le

ft

4 hy

pertr

ophy

z 0

9

z D

M A N I F E S T 1 N G C A R R I E R S 35

and there was no family history of muscle disease.

Case 6 This lady was first seen at age 51 in 1972. She had had difficulty in getting up stairs and steps for many years beforehand and when seen was using a wheelchair much of the time. Examination showed muscle weakness, mainly confined to the shoulders, biceps humeris, triceps, trunk and hips. The calves were a little bulky and CK six times the upper limit of normal. Her three sons aged 27, 24, and 15, and daughter were normal, but her younger sister suffered the same problems in approximately the same degree. Their parents were unrelated and the family history was negative. She was counselled for autosomal recessive inherit- ance. Fifteen years later the youngest son presented with a 10-year history of Miculty running, and rising from low chairs and

stooping positions. On examination he walked with a lordotic gait, had mild weak- ness of hip flexors and around the shoulder girdle, and had definite calf hypertrophy. His CK was 3210 i d - ' and muscle biopsy was compatible with BMD. We now con- sider that his aunt and mother (who has since died of an unrelated illness) were man- ifesting carriers of BMD.

Cue 7 This 15-year-old girl gave a 2-year history of difficulty running, and was unable to rise from the floor without using her hands. There was minimal weakness around the shoulder girdle, but moderate weakness of hip flexors and extensors and dorsiflexion at the ankles. She had marked calfhypertro- phy with CK 2870 iu1-I. Muscle biopsy was compatible with BMD. She has a younger sister and three younger brothers; her par-

Flg. 1. Mwcle blopsy from Case 4 showing variation in fibre slre. fibre spiltttng and Increase of intermpeal connective timue. (Haemotoxylln end Eorln x 400).

36 N O R M A N A N D HARPER

ents are unrelated. All are healthy and have CK in the normal range.

Discussion

This is the first comprehensive survey of manifesting carriers in a defined population since that of Moser & Emery (1974). We estimate that 2.5% of gene carriers are clin- ically manifesting. Moser & Emery gave a higher estimate of the proportion of Duch- enne carriers who were manifesting at 8%. It is probable that their criteria for diagnosis were less stringent; they included some pa- tients with a history of muscle cramps and raised CK without objective evidence of muscle weakness. If we had included such patients, then our detection rate would have more than doubled. Furthermore they con- sidered DMD only, whereas we have com- bined data from DMD and BMD, and felt it unwise to separate the two groups for analysis in view of the small number of manifesting carriers detected. We found four women with CK levels of 1000 i d - ' or greater, but no muscle weakness. They were younger than the manifesting carriers and it will be interesting to see whether any de- velop weakness in the future. The clinical findings in our patients were similar to those of previous studies. The CK was always raised to more than 4 times the upper limit of normal. The pelvic girdle was commonly affected, and there was a tendency to asym- metry in muscle weakness. This would fit well with the hypothesis that manifesting camers represent those heterozygotes who have inactivated a larger proportion of nor- mal Xchromosomes than DMD Xchro- mosomes in muscle tissue by chance.

The predicted frequency of manifesting carriers in the population as a whole can be estimated as follows. Taking the mutation rate p = 1 x and the proportion of car- rier females 4p, the prevalence of manifes- ting camers in Wales should be 4 x lo-' x

0.025= 10 x or 1 in 100000 of the gen- eral female population. This compares with the prevalence of LGD in Lothian of 7 x

(Yates & Emery 1985). If the mutation rates in male and female gametes are equal, then twice as many girls as boys should have a newly mutated DMD gene, and we should expect 2.5% of them to manifest it, presenting as isolated cases, and causing confusion with LGD. It appears that Cases 4-7 described above fall into this category. Since the number of BMD carriers in our series is relatively small (22/119), we have included them together with DMD camers in this estimate, even though it is possible that fewer BMD carriers are manifesting.

Based on our prevalence estimates, we suggest that females with proximal muscle weakness, grossly elevated creatine kinase, and calf hypertrophy in whom muscle bi- opsy shows primary muscle disease without other cause, such as mitochondria1 cytopa- thy or glycogen storage disease, are likely to be manifesting carriers of the Duchenne or Becker muscular dystrophy gene even in the absence of a positive family history. Analysis of DNA with probes complement- ary to the dystrophin gene (cDNA) clarifies the diagnosis in at least two thirds of iso- lated adult male patients (Norman et al. 1989). We have not so far found this ap- proach useful in female patients, because heterozygosity obscures molecular deletions and we have found gene dosage alone insuf- ficiently reliable. Other techniques such as pulse-field gel electrophoresis should allow detection of abnormal-sized fragments of the dystrophin gene in these patients, while analysis of dystrophin itself may provide further help and is being undertaken in our patients.

Acknowledgements

We thank Dr J. Graham and Prof. A. Compston for allowing us to study their

M A N I F E S T I N G C A R R I E R S 37

patients, Dr G. Cole for analysis of his- tology, and the ladies who agreed to take part in the survey. AN is supported by the Muscular Dystrophy Group.

References

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Becker, P. E. & F. Kiener (1955). Eine neue X- chromosomale Muskeldystrophie. Arch. Psy- chiat. Nervenkrankheit. 193, 427-448.

Emery, A. E. H. & J. N. WaIton (1967). The genetics of muscular dystrophy. In Progress in Medical Genetics. A. G. Steinberg & A. G. Beam (eds.) New York, Grune and Stratton, Vol 5, pp. 116145.

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Kingston, H. M., M. Sarfarazi, R. G. Newcombe, N. Willis & P. S. Harper (1985). Camcr detec- tion in Becker muscular dystrophy using cre-

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Norman, A. M., N. S. T. Thomas, J. Coakley & P. S. Harper (1989). Distinction of Becker from limb-girdle muscular dystrophy by means of dystrophin cDNA probes. Lancet i, 466-468

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Address: Dr. A. M. Norman Institute of Medical Genetics University of Wales College of Medicine Heath Park Cardff CF4 4XW United Kingdom