Results from a study conducted this month by scientists at the Samsung Medical Center in South Korea, in collaboration with LabGenomics, have revealed that hereditary neuropathy with liability to pressure palsies (HNPP), is much more common than usually assumed.
Researchers estimate that one in every 5,943 Koreans have a deletion within the PMP22 gene, which is higher than worldwide estimates which stands at every 16 out of 100,000 person with the condition. It is generally believed across the board that 2-5 of 100,000 have HNPP, however, this latest research shows it is the equivalent to every 59th person out of 100,000, many of whom may present only mild symptoms. So are there more people with HNPP than we initially thought?
South Korea
Scientists sampled DNA from 11,885 Korean newborns for the study Frequency of hereditary neuropathy with liability to pressure palsies (HNPP) due to 17p11.2 deletion in a Korean newborn population, using next-generation sequencing (NGS). In all, more than six million sequence reads were analysed using a bioinformatics platform.
The team detected seven samples of those tested with deletions of genetic content affecting the 17p11.2 chromosome – which includes the PMP22 gene – and two cases of PMP22 gene duplication leading to CMT1A. They report that all samples were from unrelated families with six out of seven being female, and three (42.9%) had a family history of HNPP.
The exact prevalence of HNPP remains unclear, however, a prior study from the Republic of Ireland and in southwestern Finland reported a prevalence of 0.84 per 100,000 to 16 per 100,000. The major difference in this study is that patients with symptoms of HNPP were tested under the Irish and Finnish report, whilst South Korean researchers analysed data from newborns.
Previously reported prevalence of hereditary neuropathy with liability to pressure palsies:
| Country | Number of cases | Estimated prevalence per 100,000 | Year | Reference |
| Republic of Ireland | 29 | 0.84 | 2017 | Lefter et al. |
| Northern England | 59 | 2.0 | 2012 | Foley et al. |
| Newcastle upon Tyne | 19 | 7.3 | 2012 | Foley et al. |
| South West Finland | 69 | 16 | 1997 | Meretoja et al. |
| South Korea | 7 | 58.9 | 2017 | Jong Eun Park et al. |
Attributed to: Frequency of hereditary neuropathy with liability to pressure palsies (HNPP) due to 17p11.2 deletion in a Korean newborn population, 2018, Jong Eun Park et al.
While the study had limitations and the number of subjects may not be adequate enough to estimate the exact prevalence of the rare genetic disorder, it still provides insight regarding the baseline frequency of the chromosome deletion that commonly causes HNPP.
As the authors say: “[A] significant proportion of parents with PMP22 duplication already have CMT1A-related symptoms and may be more likely to request prenatal genetic diagnosis or preimplantation genetic diagnosis (PGD) rather than neonatal screening.
“Our data suggest that PMP22 deletion [associated with] HNPP might not be uncommon, at least in the Korean population,” they concluded.
HNPP Wellbeing 