Definition
This rare genetic auto-inflammatory disease was first described in 2008.
Epidemiology
There are around 200 patients with the disease worldwide to date, mainly in Arab countries and India, but other cases have been described in Europe, Asia and Africa, affecting both men and women.
In the majority of cases, symptoms begin in childhood and the disease is diagnosed in adolescence.
Genetic
The disease is linked to mutations in the SLC29A3 gene located on chromosome 10, which codes for human balancing transporter number 3 (hENT3).
The presence of 2 mutations is required to cause the disease.
Both parents are usually healthy carriers and pass on a single mutation; the disease occurs more often if the parents are related (in 50% of cases described).
Clinical
In the vast majority of cases, patients present with visible birth defects such as facial dysmorphia, bone deformities with supernumerary or hooked teeth, heart or vein defects. Then, skin anomalies appear in the form of brownish +/- hyperpigmented patches on the inner thighs with extension.
This anomaly is called Hyperpigmentation/Hypertrichosis and is the most frequent feature of the disease, followed by hearing loss (Hypoacusis), growth retardation and/or short stature, deformities of the joints of the fingers or feet. Other abnormalities follow, with infiltration of tissues leading to cardiac abnormalities, enlarged liver and spleen (called Hepatosplenomegaly), reduced fertility due to Hypogonadism, and diabetes leading to Hyperglycemia.
Because of the numerous anomalies beginning with the letter H, the authors have named this disease the "H" syndrome.
Biology
Almost half of all patients have inflammation in the blood (elevated C-reactive protein or CRP) and often anemia.
Histology
When affected tissue is biopsied, a diffuse lymphohistiocytic infiltrate and/or infiltrate around vessels with marked fibrosis is observed under the microscope. The infiltrate is mainly composed of cells called histiocytes.
Diagnostic
Diagnosis of the disease is based on genetic analysis, which involves taking blood samples to look for mutations in the SLC29A3 gene.
The referring physician may offer family members a consultation to identify other people with the disease. There is no indication for genetic testing in people with no symptoms.
Evolution
The disease often progresses chronically, with deafness and diabetes the main complications.
In the event of cardiac involvement, close monitoring by a cardiologist is essential.
Treatment
Patients need specialized care in an expert center, with regular clinical and biological follow-up to monitor inflammation in the blood, diabetes and heart.
To date, there is no cure. Long-term treatment is most often necessary, particularly in cases of chronic inflammation and cardiac involvement.
Some treatments are taken orally, others by injection under the skin or by intravenous infusion.