Rare Condition Registration Statistics updated to 2021

Understanding the size of the population living with and beyond the diagnosis of a disease or condition at a point in time can support service planning for the delivery of local health and social care services, quantify the ‘burden’ of disease or number of children living with a congenital anomaly in an area or population. Therefore this could help determine the number of people who may have unmet health needs that could potentially benefit from new treatment interventions. Data are only currently presented at a national level due to the small numbers involved and the experimental nature of this release.

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This work uses data that has been provided by patients and also collected by the NHS as part of their care and support. The data are collated, maintained and quality assured by the National Disease Registration Service, which is part of NHS England.

Point prevalence rates as of 31 December 2020 for England are presented for a selection of rare diseases (rare cancers are presented further below). See the data download section below details of how the diseases were coded.

¹ For rare diseases sourced from Hospital Episode Statistics data it is the first coded record in the data period that serves as the entry point into the prevalent cohort, which is not necessarily the date of diagnosis.
² 'Porphyria' cases could not be classified into one of the more detailed subgroups
³ Potential cases of anti-neutrophil cytoplasmic antibody-associated vasculitis sourced from data coded in ICD-10 with code I776 ('Arteritis, unspecified') is not included. Where more detailed sub-groups exist (codes M301, M313 or M317) they are individually grouped, but even in total they may underestimate the overall prevalence.
⁴ Juvenile idiopathic inflammatory myopathy prevalence is sourced from ICD-10 coded data (coded as M330) which is a subgroup of Juvenile idiopathic inflammatory myopathy, as such this may underestimate the full prevalence of this condition.

Point prevalence rates as of 31 December 2020 for England are presented for a selection of congenital anomalies for children born between 2018 and 2020. See the data download section below details of how the diseases were coded.

¹Persons aged under three years only

Point prevalence rates as of 31 December 2020 for England are presented for a selection of rare cancers. See the data download section below details of how the diseases were coded.

Prevalence counts the number of individuals diagnosed with a disease who were believed to still be alive on a given index date. The index date of this release is 31 December 2020. 

These data report observed, limited-duration disease prevalence. For most diseases/conditions, the observation period is the maximum length that it is possible to reliably count individuals over time in the available data. This varies with the disease/condition due to differing methods of collection so is indicated in the data tables. For cancer prevalence a 20 year observation period is presented. This standard time period allows comparisons of prevalence over time with a fixed-length ‘data window’.

View the birth prevalence statistics for relevant congenital anomalies are published in the NCARDRS Congenital Anomaly Official Statistics Report on the NHS Digital website.

It should be noted that the population used as a denominator for the congenital anomaly prevalence is children aged less than three years (in mid 2020). This is because national congenital anomaly registration has only been in place for babies born since 1 January 2018. The point prevalence data presented represents all individuals born between 1 January 2018 and 31 December 2020, that were still alive on the index date of 31 December 2020.

Patients were included in the cohort if they met the following criteria:

1. Diagnosed with or with the disease of interest coded while receiving care in the observation period, or were born in the period and diagnosed with a congenital anomaly (in which case date of birth is used as the entry date to the prevalent cohort).
2. Could be traced on the NHS spine.
3. Resident in England at time of diagnosis of rare cancer, at time of tracing for other rare disease, or birth for congenital anomalies.
4. Alive at last day of follow up (index date): 31 December 2020.
5. The patient is diagnosed with a finalised cancer registration; with a confirmed or probable diagnosis of a (non-cancer) rare disease; or diagnosed with a confirmed or probable congenital anomaly (not necessarily prior to the index date).

The cohort of persons with rare cancers is extracted from the National Cancer Registration Dataset. The cohort of persons with congenital anomalies is extracted from the National Congenital Anomalies and Rare Disease Registration Service Dataset as described in the cohort profile, selected from conditions that may be detected as part of the Fetal Anomaly Screening Programme available from the gov.uk website.

For the (non-cancer) rare diseases presented there are two separate methods of data collection:

1. One group of diseases is based on the Rare Autoimmune Rheumatic Disease (RAIRD) cohort. This was collected as part of the RECORDER project using Hospital Episode Statistics data (sourced from NHS England) with the first mention of a disease of interest as the date of entry to the cohort. Patients receiving care outside of secondary care (or inpatient care where their rare disease is not coded) may be excluded from the prevalent cohort. These patients may have a disease of a different nature to those being treated in secondary care (possibly less advanced).
2. The other group of diseases is based on data received from highly specialised clinical services for these rare disease types on patients under their care. In some cases the diagnosis date for the disease dates back to the mid-20 century. Patients receiving care for a disease outside these highly specialised services may therefore be excluded from the prevalent cohort. Again these patients may not be representative of those treated in highly specialised care.

NDRS is working to improve registration of cancers plus rare diseases and conditions by cross referencing additional sources of data, in addition to those sources described in the links above.

Prevalence rates are calculated overall using the  (Lower layer Super Output Area) LSOA 2020 mid-year population estimates. They are expressed using different denominators: rare diseases as a count per 1,000,000 population; congenital anomalies as a count per 10,000 population; and rare cancer as a count per 100,000 population.

The rare disease and rare cancer rates use the all-age total population for England while the congenital anomaly rates use the population aged under three years old.

Confidence intervals (CIs) are computed around a point estimate (e.g., prevalence rate) to quantify the imprecision that results from natural variation in the estimate of the value and to find the range of values within which the true population value is likely to fall. In this output, CIs are based on a 95% confidence level. For rare diseases and congenital anomalies the methodology used is the Poisson distribution (Bégaud et al, 2005). For rare cancers the phe_rates function is used: where numerator counts/cases >= 10 Byar's method is used while for smaller numerator counts an exact method based on the Poisson distribution is used.

See the resources section below for a link to the function written to calculate the prevalence rates.

Due to the implementation of ICDO3 classification from 2013 some tumour site definitions are different for tumours diagnosed from 1995-2012 and 2013-2020 to reflect the use of the new coding system. For the affected groups, ICD10/O2 is used from 1995-2012 and then ICDO3 from 2013-2020. By using the ICDO3 definitions from 2013 we are ensuring we are defining the tumour groupings as per the most up to date classifications for relevant groupings.

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