Discussion
ANK1 Mutation is the most common cause of HS. ANK1 mutations is
inherited in both AD (autosomal dominant) and AR (autosomal recessive)
patterns in HS and the majority is de novo mutation [1]. These
mutations locate the entire ANK1 gene, throughout the promoter region
and coding exons [12, 13]. To date, a total of 62 mutations are
included in the HGMD public database. Missense/nonsense and small
deletions have been identified in approximately 70% of all mutations in
the ANK1 gene. Seven splicing mutations, occurring in IVS1,16,20,22,28
and 38, are included in the HGMD database. In this study, we described a
Chinese family with a proband and his mother affected by HS. A de novo
mutation (c.856C>T p.R286*) causing a premature stop codon
in exon 9 of ANK1 was found by investigating this family through NGS
followed by Sanger sequencing to certify the relationship between the
ANK1 mutation and HS.
ANK1 plays a pivotal role in the stabilization of the membrane,
providing the main membrane binding site for the spectrin-based membrane
skeleton. ANK1 consists of three structural domains: a multiple repeats
N-terminal domain(89kD), a spectrin-binding center region(62kD) and a
regulatory C-terminal domain(55kD) [7, 14, 15]. Mutations in the
spectrin-binding domain and regulatory C-terminal domains result in the
most severe anemia compared with those located in the other domains
[14, 16]. In this family, a ANK1 c.856C>T mutation
occurred in the N-terminus region. This mutation was not found in the
gnomAD ,1000G, ExAC and HGMD database, and confirmed as a novel
mutation. According to bioinformatics analyses, this point mutation
generates a premature translation termination codon resulting in a
truncated ANK1 protein, losing the important spectrin-binding and
regulatory C-terminal domains and leaving only partial of the N-domain,
which might cause HS. Moreover, consistent with the genetic diagnosis,
the symptom of the mother was ameliorated after splenectomy, further
supporting the genotype-phenotype relationship.
NGS provides a comprehensive and cost-effective approach to molecular
diagnosis of hereditary hemolytic anemia, especially in cases where
biochemical testing is unreliable due to multiple transfusions. In
previous research [17], a female individual presented with a yellow
complexion, jaundice and splenomegaly without other pathological
symptoms or signs on the second day after birth. And then the girl who
was clinically diagnosed with HS and under laparoscopic splenectomy
because of splenomegaly and hemolysis when she was 6-year-old. Finally,
using NGS detected a de novo nonsense ANK1 mutation (c.796G
> T, p. Glu266X), which caused a substitution from glutamic
acid to a premature stop at codon 266 and may lead to HS. But no
mutation was detected in her parents. Thus, it is efficient and
important for us to using NGS to identify inherited, rare gene mutations
which are associated with a high risk for the development of diseases.
If diagnosed earlier, fewer newborn infants would develop severe anemia
and hazardous hyperbilirubinemia and it would remind pediatricians to
closely monitoring of infants with HS during the first 6 months of life
that is important for appropriate clinical management.
In summary, our results demonstrated an ANK1 c.856C>T
mutation may lead to a premature stop at codon 286 and may be
responsible for HS in two patients from a Chinese family. Identifying
the underlying genetic cause not only helps with the management of the
patients, it also facilitates accurate genetic counselling and helps in
guidance regarding the predicted severity of clinical phenotype.