In this study, we included 35 pediatric patients with confirmed GSD Ib based on typical symptoms, biochemical abnormalities and specific genetic mutations. Clinical characteristics and results of auxiliary examinations were summarized. The outcomes of treatment with the SGLT2 inhibitor empagliflozin in GSD Ib patients were also discussed. The cumulative treatment time of empagliflozin was greater than 24 years. To our knowledge, this is the largest cohort of pediatric GSD Ib patients treated with empagliflozin to date.

GSD Ib was first recognized by Narisawa et al. in 1978 [25] and has received a great deal of attention since then. However, only a few studies on GSD Ib patients in the clinical have been carried out. The correlation of genotype and phenotype of GSD Ib as well as management have been extensively discussed [11, 20,21,22].

Generally, GSD Ib patients share specific clinical characteristics, including hypoglycemia, hepatomegaly, abdominal distension, intractable infection, and neutropenia, which were also exhibited by patients in our center. The population in our center had early-onset disease. 97% of patients (34/35) in our study were symptomatic or were found to have biochemical abnormalities before they reached 1 year of age and were referred to the endocrinology department. Therapy for symptoms was administered, such as immediate injection of glucose, correction of acidosis, and emergency anti-infection drugs. The outcome of treatment was generally poor, and some patients cannot survive to adulthood. In our study, 5 children died during the follow-up period of 34.5 (9.0, 71.5) months, with a fatality rate of 14.3% (5/35). Among them, 3 boys, including Patient 6, Patient 21 and Patient 25, died in infancy, while 2 girls, including Patient 11 and Patient 13, died at 12 years old and 2 years old, respectively.

Liver adenoma is considered a complication of GSD I with aging and predominantly occurs during and after puberty, with a range of prevalence from 22 to 75%. It has the potential to transform into carcinoma and result in serious complications, such as bleeding and organ compression [18, 26, 27]. Our participants did not report any relevant complaints except Patient 18, who exhibited a hepatic hemangioma on regular ultrasound examination at 7 years old. In the future, abdominal ultrasound should be considered when any signs occur or patients become adolescents or adults. The underlying mechanisms of liver adenoma are not fully understood, but good control of glucose and lipids has been found to be beneficial [27,28,29].

Genetic analysis is an effective diagnostic method that provides genotype information and successfully avoids the need for invasive liver biopsies. 122 pathogenic mutations of the SLC37A4 gene have been reported in the Human Gene Mutation Database, with the most frequent mutation types being missense mutations. Nineteen different deleterious mutations were identified in our study. The most common mutation was the missense mutation c.446G > A (p.Gly149Glu), which overwhelmingly accounted for 63% of all alleles, including 17 patients with homozygous mutation c.446G > A and 11 patients with compound heterozygous mutation c.446G > A. Qiu et al. reported that the most frequent mutation in GSD Ib patients from a tertiary care center in North China was c.572 C > T (p. Pro191Leu), which accounted for 37% of the detected alleles [21]. However, it contributed to merely 6% of all mutated alleles in our population. This difference shows that the variants of the SLC37A4 gene have some racial and regional variability in China. Moreover, in our included participants, 7 novel disease-causing SLC37A4 variants (c.454G > C, c.359delC, c.123_124dupGA, c.1117G > A, c.1210delT, c.870 + 3delG and exons 5-11del) were discovered. Our results enrich the spectrum of SLC37A4 mutations and facilitate medical practice.

As to discover the relationship between mutation and phenotype, analysis of the age of onset, blood glucose, lactic acid and neutrophil count at onset was analyzed among patients with homozygous mutation c.446G > A (n = 17), with compound heterozygous mutation c.446G > A (n = 11), and without mutation c.446G > A (n = 7). Patients with homozygous mutation c.446G > A had an onset of 5.0 (2.0,7.0) months, a little earlier than patients with heterozygous mutation c.446G > A that had an onset age of 5.0 (3.5,7.5) months, and patients without mutation c.446G > A that had an onset age of 6.0 (3.0,10.0) months. Homozygous patients didn’t have significantly different hypoglycemia (blood glucose 2.35 (1.90,4.00) mM) compared with other two groups (blood glucose 1.77 (0.80,2.47) mM and 1.92 (1.37,2.60) mM respectively). Lactic acid in homozygous patients was less than other two groups, with lactic acid in serum being 6.20 (3.62,10.10) mM, 9.70 (5.75,11.80) mM, and 10.40 (6.20,12.00) mM respectively. There was no difference among the neutrophil count in the three groups, with the number of neutrophils being 0.74 (0.65,1.21) × 109/L, 0.76 (0.60,1.16) × 109/L, and 0.62 (0.52,0.74) × 109/L respectively. However, the poor prognosis of patients with mutation c.446G > A should be paid more attention. In our study, two patients who died in infancy had compound heterozygous mutation c.446G > A, and 2 deceased girls were with homozygous mutation c.446G > A. Pathogenicity of c.446G > A was verified in 2002 [30], but now there is more evidence demonstrating that patients with the c.446G > A mutation have a more severe condition.

Effective treatment and careful nursing can prevent death, especially after 3 years of age, when the immune system becomes stronger. All patients were properly fed with UCCS daily from the time of diagnosis. A proper feeding schedule was sufficient to normalize transaminase, uric acid and triglycerides, while lactic acid was slightly higher and the size of the liver was still bigger than normal. Considering the immature metabolic system of pediatric patients, other drugs like allopurinol and fenofibrate were not used in our treatment plan. Patients with GSD Ib had a long history of recurrent infection since their babyhood. Supplementation with G-CSF could improve neutropenia, but it was difficult to achieve regular injections due to poor medical habits in China. Usually we arranged regular G-CSF injections when patients were in the hospital. As a result of failure in regular G-CSF supplementation, over half of GSD Ib patients suffered from protracted diarrhea and/or abdominal pain.

Among our cohort, nine of the patients were assessed with enteroscopy and bowel biopsy by pediatric gastroenterologists, and Crohn-like IBD was identified. Two patients received infliximab treatment for 6 months in the gastroenterology department of our hospital. Along with remission of gastrointestinal manifestations such as oral aphthous ulceration, chronic abdominal pain, diarrhea and perianal fistula or abscess, smoothing of the colonic mucosa was observed on colonoscopy after treatment. A similar result was reported by Gong in 2021, and the positive effect of infliximab on IBD in GSD Ib patients was shown [31]. Nevertheless, as for injections of G-CSF, infliximab treatment was difficult to promote among GSD Ib patients due to inconvenience with the treatment regimen. Other drugs, such as the nonsteroidal anti-inflammatory drug mesalazine, antiviral drug dipyridamole, antifungal drug itraconazole, and vitamin E, were used to control symptoms of IBD but had no significant effect on neutropenia.

Veiga-da-Cunha M et al. provided evidence that inhibitors of the kidney glucose transporter SGLT2 could reduce the level of 1,5AG6P to restore neutropenia in patients with G6PT and G6PC3 deficiency [12, 13]. Since then, the SGLT2 inhibitor empagliflozin has been used off-label to treat GSD Ib patients. In addition, empagliflozin was adopted as a drug for treatment of pediatric type 2 diabetes by the FDA in 2023. Therefore, its high safety in children is well known [14,15,16,17]. We started empagliflozin treatment in 14 GSD Ib patients in 2020. There were no standardized guidelines on empagliflozin treatment of GSD Ib, so dosages were clinically adjusted in line with patients’ age. Usually, patients under 4 years old took empagliflozin 2.5 mg q.d. or 3 mg q.d., while patients older than 4 years old took 5 mg q.d. As the follow-up data showed, empagliflozin treatment was more beneficial to neutrophil function than metabolism. The neutrophil count in patients who participated in treatment increased, and the number of infections decreased. After treatment, the frequency and interval of infection increased to at least six months. In addition, according to patients, gastrointestinal symptoms, such as abdominal pain, loose stools, diarrhea and perianal abscess, were improved after empagliflozin treatment. Although oral aphthous ulceration was still present, the pain of patients was greatly reduced. In short, the outcome of empagliflozin treatment in our cohort was in accordance with previous reports [14,15,16,17].

In order to assess IBD development and avoid invasive examinations, hematocrit, hemoglobin and platelets were compared to evaluate the effectiveness of empagliflozin in this study. Hematocrit and hemoglobin levels indicated anemia, which is a trait of chronic inflammatory disorders and IBD [32]. To date, the underlying cause of anemia in IBD is uncertain, but iron deficiency resulting from intestinal bleeding or dysfunction of iron transport mediated by inflammation are likely contributing factors [33]. Cabrera proposed that the combination of platelet count and hemoglobin level was a useful screening test for patients with suspected IBD [34]. Comparing blood count before and after empagliflozin treatment, hematocrit and hemoglobin were significantly improved, which hinted that anemia of GSD Ib patients in our cohort was ameliorated. Importantly, hemoglobin levels of all the patients were above 108 g/L that hinted that anemia was alleviated. Although platelets in some patients were decreased, a significant change was not observed. The relationship between platelets and IBD in GSD Ib patients remains to be discovered. However, improvements in the immune system were observed, including duration of infections, periodontitis, stool shape, nutrition and metabolism environment.

Although 5 patients had positive urine glucose levels in our cohort as effect of SGLT2 inhibitor, they did not suffer from urinary tract infections because of careful nursing. Hypoglycemia was occasionally mentioned in the follow-ups, but no patient was sent to the hospital with hypoglycemia. Empirically, empagliflozin taken before meals could avoid hypoglycemia.