Ferritin L-subunit Gene Mutation and Hereditary Hyperferritinaemia Cataract Syndrome: A Case Report and Literature Review

Background: Hereditary hyperferritinaemia cataract syndrome (HHCS) is an autosomal dominant disease characterized by high serum ferritin levels and juvenile bilateral cataracts. It is often caused by mutations in the Iron Response Element (IRE) of the ferritin L-subunit (FTL) gene. Most of the mutations are point mutations located in the upper stem and the conserved hexanucleotide of the hairpin structure of IRE, only a few mutations are deletions. Case presentation: Here we report a 73-year-old woman who presented to clinic with persistently elevated serum ferritin and family history of juvenile bilateral cataracts in four generations. DNA sequencing analyses identied a heterozygous c.-167C>T mutation in the 5’ untranslated region (UTR) of the FTL gene. Her daughter and granddaughter were also conrmed to have the same genetic mutation. Conclusion: HHCS should be considered in the differential diagnosis of hyperferritinemia, especially in the presence of normal serum iron concentration and transferrin saturation. For patients with unexplained hyperferritinemia and bilateral cataracts who have experienced early vision loss, the establishment of genetic counseling is essential to diagnose other family members who are at risk in time, so as to avoid unnecessary liver biopsy and venesection.


Introduction
Hereditary hyperferritinaemia-cataract syndrome (HHCS) is a rare autosomal dominant genetic disease characterized by signi cantly raised serum ferritin, bilateral congenital cataracts, but there were no other laboratory indicators of increased iron load in the body (normal or low transferrin saturation and serum iron), no increased iron load in the liver and other parenchymal organs, and no evidence of in ammation or tumor [1][2][3][4][5].
It is currently believed that the pathogenesis of HHCS is mainly due to the mutation in the segment of Iron Response Element (IRE), which is the critical sequence of the stem-loop motif that located in the 5' untranslated region (UTR) of the ferritin L-subunit (FTL) gene [6]. This region can affect the binding a nity of IRE binding protein to IRE and deregulate the expression of the L ferritin, resulting in an increased synthesis of L ferritin. The excessive ferritin subsequently accumulated in tissues and serum, leading to hyperferritinemia, L-ferritin deposition in the lens and the early onset of bilateral cataracts [7][8][9][10][11][12][13]. Kröger et al reported that the lens opacities of patients with HHCS consisted of a lot of L ferritin [14].
Mumford and colleagues found that the level of ferritin in the lens of patients with HHCS was 10-fold higher than that in the control group [15]. The severity of cataracts is related to the levels of serum ferritin [16] and the clinical severity of HHCS (including serum ferritin levels and cataract severity) is related to the location of the IRE mutation [17,13].
The main clinical manifestations of HHCS are bilateral cataract and elevated serum ferritin level. Usually, bilateral cataract may be the only recognizable phenotypic manifestation [18]. However, many clinicians often fail to identify and diagnose HHCS. They just treat the patient as a pure cataract patient, and even perform eye surgery on the patient without checking the serum ferritin concentration, ignoring the genetic characteristics of the disease [5]. Family history of hyperferritinemia and cataracts are important diagnostic indicators of HHCS. Genetic analysis of FTL gene is a simple procedure that can con rm the diagnosis [19]. Accurate diagnosis of HHCS can avoid unnecessary phlebectomy therapy and focus attention on early cataract detection in high-risk offspring.
Here, we report a Chinese female with HHCS associated with a heterozygous mutation at position + 33 (c.-167C > T, chr19:49468598) in the FTL gene. In addition, we have reviewed all the mutations of FTL gene in reported cases of HHCS until now, in order to provide experience for accurate diagnosis of similar patients.

Case Report
The patient was a 73-year-old woman, and the overall condition was fairly good. According to the patient, she had poor vision from childhood. At the age of twelve, she was diagnosed with congenital cataracts, with visual acuity 6/10 in the left eye and 7/10 in the right eye. She began to have blurred vision in both eyes since the age of 40. When she was 68 years old, the loss of her visual acuity progressed, and visual acuity was 5/10 in the left eye and 4/10 in the right eye. Then she underwent ultrasound phacoemulsi cation and intraocular lens implantation under topical anesthesia. After the surgery, her visual acuity recovered to 8/10 in the left eye and 7/10 in the right eye, with eyeglasses for correction.
She found her ferritin was elevated (2500 ng/ml, reference value 24-336 ng/ml) during a routine health check-up at the age of 71. Then the patient began to review serum ferritin regularly.
In August 2020, she visited the outpatient department of Hematology of West China Hospital for further assessment due to persistently raised serum ferritin. Repeated examination indicated that her serum ferritin concentration was signi cantly increased (1652 ng/ml, reference value 24-336 ng/ml). Further Evaluation of magnetic resonance imaging (MRI) of the heart and liver showed no evidence of parenchymal iron overload. She had no other aetiologies such as malignancy, in ammation, obesity, and alcohol abuse that could cause hyperferritinemia.
Consequently, genetic testing was carried out on the patient, Sanger sequencing was performed to identify the mutations of the FTL gene in the peripheral blood of patients, including all point mutations, small insertions, and small deletions. Genomic DNA was extracted from peripheral blood using the commercially available kits. The IRE of the FTL gene in the 5'-UTR was ampli ed by standard polymerase chain reaction (PCR) using Taq polymerase. PCR ampli cation was performed using the following primer pair: forward, 2F: 5'-GGGCTGAGACTCCTATGTGC-3', reverse, 2R: 5'-GGTTGGTTGGCAAGAAGGAG-3'. Sequence analysis of PCR products was performed on Illumina Novaseq6000 sequencing platform. A heterozygous sequence variant (c.-167C > T, chr19:49468598) was identi ed in the 5' UTR of the L-ferritin mRNA in the patient (Fig. 1). Her daughter and granddaughter were also con rmed to have the same genetic mutation.
Family history was signi cant in that the patient's mother also had early onset cataract. One of her younger brothers was diagnosed with congenital cataract at the age of 10 and underwent cataract surgery at the age of 19. The patient's daughter and granddaughter also suffered from eye problems at the age of 12, and were con rmed to have the same genetic mutation as the patient. The affected brother of the patient had a 35-year-old son who had no eye problems. The remaining healthy brother had a nonaffected daughter. No member of this family had previously had genetic counseling. The family pedigree is outlined in Fig. 2.

Literature review
We identi ed 97 cases from all the English literatures that reported HHCS from 1995 to 2020 via PubMed. The current case is the second reported case of HHCS in China. Since rst reported by Girelli et al. in 1995 [4], a series of point mutations and short deletions of L-ferritin related to HHCS have been reported. Table 1 shows that a total of 33 single nucleotide transitions and 5 nucleotide deletions have been reported as of February 2021. Among them, the single nucleotide transition most frequently reported is 40 A > G. In addition, most mutations have been reported only once. Mutations causing HHCS in the predicted IRE structure of L-ferritin are presented in Fig. 3. It can be seen from the gure that most of the mutations that cause HHCS are at the upper stem and the conserved hexanucleotide of the hairpin structure of IRE, indicating that these parts are critical for an e cient interaction of IRE and IRP.
The main clinical manifestations of the majority of individuals diagnosed with HHCS are long-term serum ferritin elevation and juvenile cataracts, while serum iron and transferrin saturation are normal. The severity of cataracts in HHCS patients is largely controlled by the binding interaction between IRE and iron regulatory proteins (IRP), and depends on the extent to which the genetic mutation changes the structure of the binding site itself [10]. Brooks et al. reported that cataract in patients with HHCS was caused by a large amount of small opacities, mainly in the lens cortex, which is a ferritin crystal that diffracts light [8]. Often, the symptoms of cataracts can be ameliorated by surgery. SNT: single nucleotide transition.

Discussion And Conclusion
In this report, we described a Chinese family diagnosed with HHCS who were identi ed a heterozygous c.-167C > T mutation in the 5' UTR of the FTL gene. This mutation has also been reported to be associated with HHCS previously in several other pedigrees [43,8,19,44,45,39,46].
According to a study by Australian scholars, the prevalence of HHCS in the population is at least 1/20,000 [3]. Since the rst case of HHCS in China reported in 2020 [33], our case is the second identi ed case. This may be due to the fact that the actual incidence of the disease in the Chinese population is relatively low, or it may be that the understanding of the disease is still insu cient, and the rate of missed diagnosis and misdiagnosis is still high.
As the increase of L ferritin in affected individuals is due to the dysregulation of L ferritin synthesis and has nothing to do with the body iron storage, there is no real iron overload in HHCS patients. In our case, the level of serum iron and TIBC was normal and MRI of liver and heart showed no evidence of iron overload. Patients with HHCS often develop cataracts at young age. Just as in our case, the proband, her daughter, granddaughter and younger brother all started to develop cataracts around the age of twelve.
The typical cataract of HHCS has unique morphological features, which are characterized by progressive white spots along the axial and surrounding areas, accompanied by small crystal aggregates [3]. Unfortunately, since the patient had undergone cataract surgery before diagnosis, we were unable to obtain the photos of patient's eye before surgery.
HHCS should be considered in the differential diagnosis of hyperferritinemia, especially in the presence of normal serum iron concentration and transferrin saturation. Serum ferritin levels can be effectively used to screen suspicious families for this condition. For patients with bilateral cataracts who have experienced early vision loss, the establishment of genetic counseling is essential to diagnose other family members who are at risk in time, so as to avoid unnecessary procedural biopsy and phlebotomy, the latter would make the patients develop iron-de cient anemia rapidly, without any improvement in the elevated serum ferritin. We recommend that patients with cataracts at young age should routinely test serum ferritin levels. On the other hand, individuals with unexplained high level of serum ferritin should be referred for ophthalmological consultation. In summary, although HHCS is a rare disorder, clinicians should be aware of it in order to avoid unnecessary treatment to deplete iron, as well as enable patients to conduct appropriate genetic counseling and more appropriate management. For example, early genetic diagnosis can be used for screening the offspring with pathogenic mutations in test-tube baby so as to prevent the disease from being inherited.