Autoimmune hemolytic anemia and thrombocytopenia in a Chinese patient with heterozygous NBAS mutations: Case report

RATIONALE

Neuroblastoma amplified sequence (NBAS)-associated disease is an autosomal recessive disorder and a broad spectrum of clinical symptoms has been reported. However, autoimmune mediated hemolytic anemia (AIHA) is rarely reported in NBAS disease.

PATIENT CONCERNS

A now 21-year-old male harbors heterozygous variants of c.6840G>A and c.335 + 1G>A and was found had retarded growth, hypogammaglobulinemia, B lymphopenia, optic atrophy, horizontal nystagmus, slight splenomegaly and hepatomegaly since childhood. This case had normal hemoglobin level and platelet count in his childhood. He developed AIHA first in his adulthood and then thrombocytopenia during the treatment of AIHA. The mechanism underlying a case with pronounced hypogammaglobulinemia and B lymphopenia is elusive. In addition to biallelic NBAS mutations, a germline mutation in the ANKRD26 (c.2356C>T) gene was also detected. So either autoimmune or ANKRD26 mutation-mediated thrombocytopenia is possible in this case.

INTERVENTION AND OUTCOME

He was initially managed with steroid and intermittent intravenous immunoglobulin supplement. After treatment, he responded well with a normalization of hemoglobin and serum bilirubin. But the patient subsequently experienced severe thrombocytopenia in addition to AIHA. He was then given daily avatrombopag in addition to steroid escalation. He responded again to new treatment, with the hemoglobin levels and platelet counts went back to the normal ranges. Now he was on de-escalated weekly avatrombopag and low-dose steroids maintenance.

CONCLUSION

The phenotype of this case indicates that c.335 + 1G>A NBAS variant is probably a pathogenic one and c.2356C>T ANKRD26 variant is improbably a pathogenic one. AIHA may respond well to steroid even when happened in patients with NBAS disease.

Evolution and expression of chimeric POTE-actin genes in the human genome

We previously described a primate-specific gene family, POTE, that is expressed in many cancers but in a limited number of normal organs. The 13 POTE genes are dispersed among eight different chromosomes and evolved by duplications and remodeling of the human genome from an ancestral gene, ANKRD26. Based on sequence similarity, the POTE gene family members can be divided into three groups. By genome database searches, we identified an actin retroposon insertion at the carboxyl terminus of one of the ancestral POTE paralogs. By Northern blot analysis, we identified the expected 7.5-kb POTE-actin chimeric transcript in a breast cancer cell line. The protein encoded by the POTE-actin transcript is predicted to be 120 kDa in size. Using anti-POTE mAbs that recognize the amino-terminal portion of the POTE protein, we detected the 120-kDa POTE-actin fusion protein in breast cancer cell lines known to express the fusion transcript. These data demonstrate that insertion of a retroposon produced an altered functional POTE gene. This example indicates that new functional human genes can evolve by insertion of retroposons.