Since the first description of GA1 patients in 1975, over 600 individuals with GA1 have been documented to date [3]. The birth incidence of GA1 varies between 1:30,000 and 1:100,000 newborns, but much higher prevalence (1:200 to 1:2300) was reported in certain groups such as the Old Order Amish, Irish Travelers, Canadian Ojibway-Cree Indians and black South Africans [11]. The exact incidence of GA1 in China remains unclear, the first multicenter pilot study revealed that the incidence was 1 in 185,971newborns in mainland China [12]. In recent years, an increasing number of GA1 patients were detected during NBS as the accumulation of screening experience and the improvement of genetic diagnosis ability [13, 14]. The incidence of GA1 in the selected southern Chinese population was about 1 in 47,044 births, which is comparable to other studied populations [15, 16]. Comparing with the incidence reported in different regions of China, the local incidence is higher that reported in Zhejiang province (1:64,708) and Jiangsu province (1:89,335) in southern China [17, 18], and Xi’an city (1:73,076) in northern China [19].
All thirteen GA1 patients in this study were identified through NBS. Interestingly, three patients were found to have GA1 due to the low C0 levels during NBS, rather than typical elevation of C5DC levels, including one neonatal GA1 and two maternal GA1 patients. The neonatal GA1 patient with low C0 level suggestive of primary carnitine deficiency (PCD) while just the contrary to a typical GA1. To our knowledge, this is the first report of neonatal GA1 case with low C0 level diagnosed through NBS. In comparison, both maternal GA1 patients exhibited typical elevated C5DC levels but along with low C0 levels that were significantly different from those of newborns. Therefore, data from this study revealed that PCD should be included in the differential diagnosis for GA1.
Although NBS has a positive effective for GA1 and is a cost-effective diagnostic strategy [20], false-negative results may occurred and several cases missed during NBS due to many factors have been reported [8, 15, 21–23]. The most common factor was that GA1 patients with LE phenotype have normal C5DC levels would escape detection, as evidenced by one of our patients (no. 7) whose C5DC level was far below the upper limit of cutoff value. Unlike the previously reported cases [8, 15, 22, 23], the patient had persistently low C0 levels thus was accidentally detected. The patient would not have been correctly diagnosed if targeted exome sequencing had not been conducted, indicating the importance of performing multigene panel testing in newborns with low C0 levels. Another factor that led to missed cases was GA1 patients had an initially elevated C5DC levels but normalized on second screen, which may be caused by secondary carnitine depletion. In addition, improper setting of cutoff values or laboratory interpretation error were responsible for some missed cases.
Adult-onset GA1 is extremely rare. Only few adult cases have been reported so far, and most of which were asymptomatic female patients who were incidentally diagnosed due to the abnormal NBS results of their infants [24–27], This study described two asymptomatic maternal GA1 patients with detail acylcarnitine profiles, which helps to better understand this disorder. The identification of maternal GA1 patients is an additional benefit because these seemingly asymptomatic mothers may develop neurological symptoms, and the preventive metabolic therapy can prevent neurological deterioration.
At least 240 pathogenic GCDH variants have been reported thus far, and several common pan-ethnic pathogenic variants have been identified (http://www.hgmd.cf.ac.uk). In particular, c.1204C > T (p.Arg402Trp) was found to be highly prevalent in several populations, which with a frequency of 12–40% in western Europe, 57% in Spain, 50% in Poland, 18.8% in India, and 56.38% in Russia [11, 28]. However, the variant was absent in Japan and was rarely identified in this cohort and previously reported Chinese patients [29–31], indicating ethnic specificity. c.1244-2A > C was reported as the common variant in southern Chinese origin, while it was not prevalent in other Chinese groups [32–34]. Consistent with previous studies [32, 33], c.1244-2A > C was the most common GCDH variant detected in this cohort of patients, with a high allelic frequency of 54.55%. Thus, the GCDH variant spectra vary significantly between ethnicities, which may also differ among different populations in the same ethnic group. In general, the GCDH variant spectra in this study was quite heterogeneous except for the observed recurrent variant. The newly identified variants in this study expanded the GCDH variant spectra. Combining the in silico prediction tools with protein modelling analysis can further reinforce the reliability of the prediction results.
In summary, this study investigated thirteen Chinese patients with GA1 identified via NBS. The incidence of GA1 in the selected population was estimated to be 1 in 47,044 newborns. The c.1244-2A > C was the most common GCDH variant. The newly identified variants further expanded the GCDH variant spectra. GA1 patients may show only with low C0 levels at the initial screening and recall stages that may be overlooked. Maternal GA1 patients can also be detected during NBS duo to the low C0 levels in their infants. Therefore, PCD should be included in the differential diagnosis for GA1, and multigene panel testing should be performed in newborns with low C0 levels.