Genetic studies by NGS Panels
Panel for Hemochromatosis, Ferroportin Disease and Hyper- / Hypoferritinemia (Code 10010)
Hemochromatosis (HC) is a group of genetic diseases characterized by excessive accumulation of iron in tissues. Following the new classification of HC there are 4 types of HC (Girelli et al. 2022 Blood): HFE-related, non-HFE-related, digenic and HC molecularly undefined.
HFE-related Hemochromatosis (HC) (before named HC type 1), also called classic hemochromatosis (OMIM # 235200) is the most common form of HC and is mainly due to Cys282Tyr homozygous mutation of the HFE gene. HFE-related HC comprises the genotypes: p.Cys282Tyr in homozygosity or compound heterozygosity of p.Cys282Tyr with other rare HFE pathogenic variants or HFE deletion. HFE HC has a low penetrance; consider presence of host-related or environmental cofactors for iron overload. In subjects with other HFE genotypes (eg, p.Cys282Tyr/ His63Asp compound heterozygosity or p.His63Asp homozygosity) consider second-line genetic testing for rarer variants.
HFE-related HC affects men more than women. From a clinical standpoint, the disease begins between 30 and 50 years of age. HC causes chronic fatigue, dark pigmentation of the skin and can severely affect the liver, pancreas, joints, bones, endocrine glands, or heart, resulting in various complications that appear in adulthood, such as hepatic fibrosis (cirrhosis with hepatocellular carcinoma risk), diabetes mellitus, arthropathy, osteoporosis, hypogonadotropic hypogonadism and heart failure. Biochemical abnormalities include elevated serum iron, serum transferrin saturation and serum ferritin levels. The molecular genetic blood test, showing a homozygous Cys282Tyr, confirms the diagnosis of HC in a non-invasive way.
Non-HFE-related Hemochromatosis (HC) (before named HC type 2a OMIM # 602390, 2b OMIM # 602390, 3 OMIM # 604250 and 4b). HC due to rare pathogenic variants in “non-HFE” genes including HJV, HAMP, TFR2 and SLC40A1 (only GOF mutations in SLC40A1 are considered as non-HFE-related HC). HJV, HAMP and TFR2-related Hemochromatosis are inherited in autosomal recessive manner and SLC40A1 (GOF)-related Hemochromatosis has autosomal dominant inheritance Patients with gain-of-function (GOF) mutations in SLC40A1 (encoding for ferroportin) presents elevated serum ferritin and transferrin saturation and hepatic iron overload in hepatocytes what can lead to hepatomegaly and cirrhosis. GOF mutations in SLC40A1 confer resistance to ferroportin to be degraded by interaction with the hormone hepcidin. This type of HC is less common than Ferroportin disease (formally known as HC type 4a). Potentially, mutations in any hepcidin-regulatory gene may be causative (the effects of novel mutations should be confirmed through functional and epidemiological studies). Indeed, variants in the BMP6 gene, encoding one of the major activators of hepcidin expression in response to iron, have been described in patients with iron overload (although those patients also have concomitant acquired cofactors for developing iron overload, i.e. alcoholism or HCV). Molecular sub-types characterization should be done only at specialized centers, but the diagnosis of non-HFE related HC is sufficient to start phlebotomies at non-specialized centers.
Digenic Hemochromatosis (HC) when we found a patient with double heterozygosity and/or double homozygosity/heterozygosity for mutations in 2 different genes involved in iron metabolism (HFE and/or non-HFE genes). More commonly, p.Cys282Tyr mutation in HFE gene might coexist with mutation in other genes; rarely, both mutations involve non-HFE genes.
Molecularly undefined Hemochromatosis (HC) when molecular characterization is (still) not available after sequencing of known genes (provisional diagnosis). Patients should be referred (or DNA should be sent) to specialized centers
HC treatment consists of phlebotomy (blood draws), initially these are made weekly, generally reducing in frequency. HC has a very good prognosis if diagnosed early and treated appropriately before the development of serious complications.
Ferroportin disease (formally known as HC type 4a) is due to loss of function mutations in the SLC40A1 gene that encodes for the iron exporter ferroportin. FD is more common than non-HFE-related HC due to GOF mutations in SLC40A1. FD is usually asymptomatic without any complications or hepatic iron overload in the future. This disease is characterized by elevated serum ferritin but normal values and / or low transferrin saturation and a tendency to anemia in patients who have been given phlebotomy. Iron overload occurs in macrophages of the reticuloendothelial system of the spleen and liver, but not in hepatocytes. The course of this disease is rather benign nature.
Hereditary Hyperferritinemias
Ferritin is the protein responsible for the storage and intracellular distribution of iron. It consists of two subunits called L-ferritin and H-ferritin. The synthesis of these subunits is controlled by regulatory proteins called Iron-regulatory proteins (IRPs) that bind to a regulatory element called iron-responsive element (IRE) present in the 5’UTR of mRNA of each of these two subunits.
In 1995 the Hereditary Hyperferritinemia Cataract Syndrome (HHCS) (OMIM # 600886) was first described. It is characterized by elevated levels of serum ferritin without iron overload, congenital cataracts and autosomal dominant inheritance. Excessive production of ferritin is due to mutations in the regulatory element called Iron-responsive element (IRE) light chain gene-ferritin L (FTL). Ferritin excess accumulates in the lens which leads to the development of cataracts. The degree of affectation varies even between individuals with the same mutation. A correct genetic diagnosis of this disease is important, as it is often confused with hereditary hemochromatosis due to the high levels of serum ferritin present in both diseases.
The overproduction of serum ferritin may also be due to mutations in the coding sequence of the gene for L-ferritin. In 2009 Kannengiesser and colleagues described a new form of genetic hyperferritinemia, known as benign hyperferritinemia without iron overload, with dominant inheritance (Kannengiesser C, et al. Haematologica. 2009).
In 2001, Kato and colleagues described a mutation of the regulatory element IRE (iron-responsive element) located in the 5 ‘UTR of the gene for ferritin-H (fth1) in a Japanese family with an iron overload syndrome and pattern of dominant inheritance (Kato et al. Am. J. Hum. Genet. 69:191-197, 2001) (OMIM # 134770). According to this study, this mutation produces iron overload in liver, pancreas and heart, and elevated serum iron and ferritin.
In 2023, Monfrini and collaborators described ten subjects from seven families with hereditary hyperferritinemia without iron overload (AR inheritance) and bi-allelic mutations in the STAB1 gene.
Hereditary Hypoferritinemias without iron overlad or neurodegeneration
Reported pathogenic variants in the FTL gene have been linked to both autosomal dominant and recessive L-ferritin deficiency, resulting in hypoferritinemia (OMIM#615604, ORPHA:440731). This condition manifests without associated iron overload, as well as the absence of neurological or hematological symptoms.
Autosomal recessive L-Ferritin deficiency was reported in 2 cases with undetectable serum ferritin levels and homozygous nonsense (Glu104Ter) or missense (Tyr31Cys) mutations (Cozzi et al 2013; Shagidov D et al 2023) .
Autosomal dominant L-Ferritin deficiency was reported in 3 cases with low serum ferritin levels with a heterozygous start-loss mutation (Met1Val) (2 cases) or a heterozygous splicing mutation (c.375+2T) (Cremonesi et al 2004; Cadenas et al. 2019).
For neurodegeneration with brain iron accumulation type 3 (NBIA3) or neuroferritinopathy, caused by heterozygous mutation in the FTL gene, see panel 10120.
References
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· Kato, J., Fujikawa, K., Kanda, M., Fukuda, N., Sasaki, K., Takayama, T., Kobune, M., Takada, K., Takimoto, R., Hamada, H., Ikeda, T., Niitsu, Y. A mutation, in the iron-responsive element of H ferritin mRNA, causing autosomal dominant iron overload. Am. J. Hum. Genet. 69: 191-197, 2001. [PubMed: 11389486]
· Monfrini E, Pelucchi S, Hollmén M, Viitala M, Mariani R, Bertola F, Majore S, Di Fonzo A, Piperno A. A form of inherited hyperferritinemia associated with bi-allelic pathogenic variants of STAB1. Am J Hum Genet. 2023 Aug 3;110(8):1436-1443. doi: 10.1016/j.ajhg.2023.07.004. Epub 2023 Jul 24. PMID: 37490907; PMCID: PMC10432174.
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· Roetto, A., Papanikolaou, G., Politou, M., Alberti, F., Girelli, D., Christakis, J., Loukopoulos, D., Camaschella, C. Mutant antimicrobial peptide hepcidin is associated with severe juvenile hemochromatosis. Nature Genet. 33: 21-22, 2003. [PubMed: 12469120]
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· Shagidov D, Guttmann-Raviv N, Cunat S, Frech L, Giansily-Blaizot M, Ghatpande N, Abelya G, Frank GA, Aguilar Martinez P, Meyron-Holtz EG. A newly identified ferritin L-subunit variant results in increased proteasomal subunit degradation, impaired complex assembly, and severe hypoferritinemia. Am J Hematol. 2023 Oct 23.