Social deprivation in Duchenne muscular dystrophy: population based study

Duchenne muscular dystrophy is an X linked disorder affecting approximately 1 in 3500 male live births. The incidence remains stable in most populations, maintained by a high rate of new mutations in the dystrophin gene.¹ We observed that a higher than expected proportion of families of patients with Duchenne muscular dystrophy seemed to be from a deprived background, even at the time of first diagnosis (usually by age 5). We measured the level of material deprivation based on the place of residence at the time of diagnosis of all patients with Duchenne muscular dystrophy in the north of England to test the hypothesis that this single gene disorder is associated with social deprivation.

Participants, methods, and results

Records of children with Duchenne muscular dystrophy in the Northern region of England have been scrupulously maintained since the 1960s, and we believe that ascertainment in the region is complete. We analysed data from the whole group of families with Duchenne muscular dystrophy in the region and also subdivided the group into four categories according to the origin of the mutation in the family (table).

In all, 229 of the 246 families with children diagnosed as having Duchenne muscular dystrophy between 1967 and 1999 in the Northern region had valid postcodes available at diagnosis. We linked patients' postcodes to data from the latest national census by using the central postcode directory, which provides a link between postcodes and enumeration districts consisting of 100-150 households. No enumeration district contained more than one affected family, and each family was counted as a single case irrespective of the number of boys affected.

We used a non-parametric test (Mann-Whitney U test) to compare the Townsend scores² for enumeration districts in which cases of Duchenne muscular dystrophy occurred against all enumeration districts in the region without cases, for all cases and for the four subgroups. We then used Monte Carlo analysis to compare the mean and distribution of scores for the enumeration districts of all affected families with the distribution of Townsend scores derived from repeated random samples of enumeration districts.

The results (table) show large and significant differences between the Townsend scores of affected families and Townsend score distributions for the rest of the population (corrected for the number of children aged 5 and under). The differences occurred in all of the subgroups. The Monte Carlo analysis confirmed the difference between affected families and the rest of the population—the mean Townsend score for the affected boys was at least 2.5 standard deviations greater than that for the random control groups in every iteration.

Comment

As a group, patients with Duchenne muscular dystrophy have significantly greater material deprivation at diagnosis than the average of the population from which they are drawn. This is evident even in families where the disease is known to be the result of a new mutation. We can find no simple explanation for this effect, but it seems that new mutations in the dystrophin gene do not occur randomly in the population. The rate of new germline mutations in the dystrophin gene is particularly high,¹ and the mechanisms by which these mutations occur are poorly understood. Further studies are needed to determine what aspects or covariates of deprivation may contribute to this effect and whether this ecological association occurs for other genes with a high level of new mutations.

Patients from deprived backgrounds have less access to health care than people from more affluent areas,³,⁴ and diagnosis of Duchenne muscular dystrophy is often delayed.⁵ Children with Duchenne muscular dystrophy have a lifelong need for the highest quality of care, and the relatively high levels of deprivation associated with the disease may restrict availability of the sustained, high quality, specialised support needed.

Table.

Townsend scores of enumeration districts with and without families with Duchenne muscular dystrophy

Group	Duchenne muscular dystrophy					No Duchenne muscular dystrophy (n=6624)		Significance
	No	Median	Range	Interquartile range		Median	Interquartile range
All cases	229	3.44	−5.74 to 10.12	0.34 to 5.45		1.46	−2.04 to 4.74	P<0.0001
History in earlier generation	42	3.15	−5.74 to 10.12	0.65 to 5.05		1.46	−2.04 to 4.74	P<0.0001
New mutation in mother	62	4.45	−4.71 to 9.59	1.76 to 5.63		1.46	−2.04 to 4.74	P<0.0001
New mutation in child	40	2.63	−5.66 to 8.46	−0.38 to 4.96		1.46	−2.04 to 4.74	P=0.001
No earlier history: mutation origin unknown	85	3.35	−2.63 to 7.41	−1.87 to 5.36		1.46	−2.04 to 4.74	P<0.0001