Poikiloderma with neutropenia (PN) is a disorder that mainly affects the skin and the immune system. This condition begins with a bumpy rash that usually appears between the ages of 6 and 12 months, gradually spreading from the arms and legs to the torso and face. At about age 2, the rash fades, and the affected child is left with darker and lighter patches of skin coloring (hyperpigmentation and hypopigmentation) and small clusters of blood vessels just under the skin (telangiectases); this combination is known as poikiloderma. Other skin problems include unusually thick skin on the palms of the hands and soles of the feet (palmoplantar keratoderma); calcium deposits that form small nodules (calcinosis cutis), especially on the knees, elbows, or ears; or sores (ulcers) that do not easily heal. Affected individuals also have fingernails and toenails that are thick and abnormally shaped (pachyonychia), fragile teeth, and low bone density.

People with PN have chronic neutropenia, which is a persistent shortage (deficiency) of neutrophils. Neutrophils are a type of white blood cell that plays a role in inflammation and in fighting infection. Neutropenia makes it more difficult for the body to fight off pathogens such as bacteria and viruses. As a result, people with PN experience recurrent sinus infections and pneumonia, especially in the first few years of life. They often develop a condition called bronchiectasis, which damages the passages leading from the windpipe to the lungs (bronchi) and can cause breathing problems. The infections become less frequent after early childhood, but throughout life affected individuals usually have a chronic cough or a reactive airway disease. This term describes asthma and other conditions in which the airways abnormally constrict in response to stimuli such as smoke or a viral infection, leading to wheezing and shortness of breath.

Researchers suggest that PN may increase the risk of cancer, although the level of risk is difficult to determine because only a small number of people have been diagnosed with PN. A type of skin cancer called squamous cell carcinoma, a precancerous blood disorder known as myelodysplastic syndrome (MDS), and a blood cancer called acute myelogenous leukemia that often follows MDS have occurred in a few people with PN.

Some individuals with PN also develop unusual facial features as they grow. These features include a prominent forehead (frontal bossing), widely spaced eyes (hypertelorism), a flat or sunken appearance of the middle of the face (midface hypoplasia), a small nose with a depressed nasal bridge, and a chin that protrudes (prognathism). Short stature and hypogonadotropic hypogonadism (a condition affecting the production of hormones that direct sexual development) can also occur in this disorder.

The prevalence of PN is unknown; only about 100 affected individuals have been described in the medical literature. Although it was first described in the Navajo population of the southwestern United States, it has since been identified in other individuals worldwide.

PN is caused by mutations in the USB1 gene. This gene provides instructions for making an enzyme that functions as an RNA exonuclease. RNA exonucleases cut off (cleave) building blocks called nucleotides one at a time from molecules of RNA (a chemical cousin of DNA). This process helps stabilize the RNA and protects it from damage. Specifically, the USB1 enzyme protects a small RNA molecule called U6, which helps in the assembly of the blueprints for protein production.

Different versions (isoforms) of the USB1 enzyme are produced in different tissues, where they play various roles. In blood-forming tissues, the USB1 enzyme is thought to play a role in the maturation of neutrophils. In the skin, the enzyme is found in pigment-producing cells (melanocytes), cells in the outer layer of the skin called keratinocytes, and structural cells called fibroblasts. Its role in the function of these cells is unknown.

Mutations in the USB1 gene are thought to lead to an enzyme whose function is impaired. As a result of the dysfunctional USB1 exonuclease, the U6 RNA is not protected from damage. The specific connection between USB1 gene mutations and the signs and symptoms of PN is unknown. However, the existence of tissue-specific isoforms of the enzyme could help explain why this disorder mainly affects the skin and immune system.

Genetic Testing Information

• Genetic Testing Registry: Poikiloderma with neutropenia

Genetic and Rare Diseases Information Center

• Poikiloderma with neutropenia

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Catalog of Genes and Diseases from OMIM

• POIKILODERMA WITH NEUTROPENIA; PN

Scientific Articles on PubMed

• PubMed

• Arnold AW, Itin PH, Pigors M, Kohlhase J, Bruckner-Tuderman L, Has C. Poikiloderma with neutropenia: a novel C16orf57 mutation and clinical diagnostic criteria. Br J Dermatol. 2010 Oct;163(4):866-9. doi: 10.1111/j.1365-2133.2010.09929.x. Epub 2010 Sep 7. Citation on PubMed
• Colombo EA, Bazan JF, Negri G, Gervasini C, Elcioglu NH, Yucelten D, Altunay I, Cetincelik U, Teti A, Del Fattore A, Luciani M, Sullivan SK, Yan AC, Volpi L, Larizza L. Novel C16orf57 mutations in patients with Poikiloderma with Neutropenia: bioinformatic analysis of the protein and predicted effects of all reported mutations. Orphanet J Rare Dis. 2012 Jan 23;7:7. doi: 10.1186/1750-1172-7-7. Citation on PubMed or Free article on PubMed Central
• Farruggia P, Indaco S, Dufour C, Lanza T, Mosa C, Macaluso A, Milioto M, D'Angelo P, Lanciotti M. Poikiloderma with neutropenia: a case report and review of the literature. J Pediatr Hematol Oncol. 2014 May;36(4):297-300. doi: 10.1097/MPH.0b013e31829f35e7. Citation on PubMed
• Hilcenko C, Simpson PJ, Finch AJ, Bowler FR, Churcher MJ, Jin L, Packman LC, Shlien A, Campbell P, Kirwan M, Dokal I, Warren AJ. Aberrant 3' oligoadenylation of spliceosomal U6 small nuclear RNA in poikiloderma with neutropenia. Blood. 2013 Feb 7;121(6):1028-38. doi: 10.1182/blood-2012-10-461491. Epub 2012 Nov 27. Citation on PubMed
• Koparir A, Gezdirici A, Koparir E, Ulucan H, Yilmaz M, Erdemir A, Yuksel A, Ozen M. Poikiloderma with neutropenia: genotype-ethnic origin correlation, expanding phenotype and literature review. Am J Med Genet A. 2014 Oct;164A(10):2535-40. doi: 10.1002/ajmg.a.36683. Epub 2014 Jul 16. Citation on PubMed
• Mroczek S, Dziembowski A. U6 RNA biogenesis and disease association. Wiley Interdiscip Rev RNA. 2013 Sep-Oct;4(5):581-92. doi: 10.1002/wrna.1181. Epub 2013 Jun 14. Citation on PubMed
• Mroczek S, Krwawicz J, Kutner J, Lazniewski M, Kucinski I, Ginalski K, Dziembowski A. C16orf57, a gene mutated in poikiloderma with neutropenia, encodes a putative phosphodiesterase responsible for the U6 snRNA 3' end modification. Genes Dev. 2012 Sep 1;26(17):1911-25. doi: 10.1101/gad.193169.112. Epub 2012 Aug 16. Citation on PubMed or Free article on PubMed Central
• Shchepachev V, Azzalin CM. The Mpn1 RNA exonuclease: cellular functions and implication in disease. FEBS Lett. 2013 Jun 27;587(13):1858-62. doi: 10.1016/j.febslet.2013.05.005. Epub 2013 May 15. Citation on PubMed
• Volpi L, Roversi G, Colombo EA, Leijsten N, Concolino D, Calabria A, Mencarelli MA, Fimiani M, Macciardi F, Pfundt R, Schoenmakers EF, Larizza L. Targeted next-generation sequencing appoints c16orf57 as clericuzio-type poikiloderma with neutropenia gene. Am J Hum Genet. 2010 Jan;86(1):72-6. doi: 10.1016/j.ajhg.2009.11.014. Epub 2009 Dec 10. Erratum In: Am J Hum Genet. 2010 Sep 10;87(3):445. Citation on PubMed or Free article on PubMed Central
• Walne AJ, Vulliamy T, Beswick R, Kirwan M, Dokal I. Mutations in C16orf57 and normal-length telomeres unify a subset of patients with dyskeratosis congenita, poikiloderma with neutropenia and Rothmund-Thomson syndrome. Hum Mol Genet. 2010 Nov 15;19(22):4453-61. doi: 10.1093/hmg/ddq371. Epub 2010 Sep 3. Citation on PubMed or Free article on PubMed Central
• Wang L, Clericuzio C, Larizza L, Concolino D. Poikiloderma with Neutropenia. 2017 Oct 26 [updated 2024 Feb 22]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from http://www.ncbi.nlm.nih.gov/books/NBK459118/ Citation on PubMed