Molecular genetic screening of full-term small for gestational age

In 2010, about 32.4 million SGA newborns (27% of live births) were born in low- and middle-income nations. Among them, 10.6 million were FT-SGA [14]. China had an incidence of SGA of approximately 6.5% [14], ranking among the top 5 countries in the world. A recent survey showed a prevalence of SGA of about 12.28% in Guangdong Province, China [15]. Therefore, special attention should be paid to SGA because of its high incidence.

More and more studies have shown that SGA may also be caused by gene polymorphism and mutation [16‐18]. However, no large sample trials with DBSs in SGA have been carried out. Therefore, we applied the novel genome sequencing project (“Angel Care”) utilizing the GS technology in FT-SGA, which detected 159 disease-associated genes.

By Angel Care GS, we detected two heterozygous and one homozygous pathogenic mutations in the DUOX2 gene which associated with TDH6 and congenital hypothyroidism (CH). It was previously demonstrated DUOX2 is the commonest gene mutation in Chinese pediatric CH cases [19], and a high degree of phenotypic heterogeneity was observed [20]. Recently, we hypothesized that CH may lead to abnormal fetal growth and development, which not only is manifested at birth, but also becomes more serious through epigenetic regulation, leading to permanent physiological and metabolic changes. In the long run, even in adulthood, this may cause mental retardation and underdevelopment, which may last for generations. Early detection, diagnosis and treatment is necessary to improve infants’ survival and quality of life.

Currently, diagnostic and treatment methods for CH are established, and NBS can be utilized for early CH diagnosis by detecting TSH and FT4. However, in SGA infants, TSH levels surge lightly after birth, and the initial serum total FT4 concentrations are lower compared with those of normal term infants, leading to a decrease during the first few days after birth rather than an increase as seen in normal term infants [21]. These differences may contribute to the missed diagnosis of CH by NBS. The results of this study indicated that the Angel Care GS provides a higher rate of neonatal disease screening compared with NBS.

In addition, valuable carrier information and cases of genetic disease carrier status were detected in this study. The genetic disease with the highest number of valuable carriers was DFNB (15/45, 33.3%). Detecting neonatal hearing abnormality early may reduce the negative effects on speech and language functions. Appropriate tests to screen for hearing impairment are available, including Otoacoustic Emission and Auditory Evoked Potential. However, there is a lack of uniformity in protocols adopted within newborn hearing screening [22]. On the other hand, ≥ 50% of congenital or childhood hearing loss cases involve genetic factors. In non-syndromic hearing loss, accounting 70% of all genetic hearing loss, about 80%, 15% and 1–2% of cases are autosomal recessive, autosomal dominant, and mitochondrial or X-linked, respectively. Currently, > 140 deafness-associated genes are known. Reports assessing such genes provided great molecular insights into the inner ear’s functions [23]. Mutations in the GJB2 gene drive up to 50% of pre-lingual, recessive deafness [24]. In this study, the most heterozygous pathogenic mutations in GJB2 was c.109G > A (p.Val37Ile), which has been confirmed to be pathogenic for Autosomal Recessive Deafness 1 A (DFNB1A) [25, 26]. The carriers are currently undiagnosed but may be more susceptible to hearing loss in childhood and even adulthood.

The genetic disease with the second highest number of valuable carriers was abnormal thyroid hormone (6/45, 13.3%). These variants of carrier status were located in DUOX2 and DUOXA2 Genetic factors, in particular mutations in DUOX2 and DUOXA2 is a major contributor to the overall increase in the incidence of CH and transient congenital hypothyroidism (TCH) [27, 28]. Therefore, the neonatal DUOXA2 gene variant should also be of concern to us. Another genetic disease with valuable carriers, KD is an autosomal recessive lysosomal disease and characterized by neurodegeneration, whose severity depends on the age of onset. Consistent with the results of our study in Table 3, the genetic loss of function of the lysosomal enzyme galactocerebrosidase (GALC) leads to KD. And the incidence of KD by newborn screening in USA was 1 in 55,000 to 418,000 births [29]. Up to now, hematopoietic cell transplantation is the only currently available treatment of infants with KD with high healthcare costs [30]. Especially in infantile KD patients, earlier treatment may mean better outcome. Therefore, early screening may improve the prognosis of children with KD.

As a consequence, this study provides critical insights, which could allow personalized and correct genetic counseling. These data may help plan future treatment management, particularly in reproductive planning. In fact, whether reporting carrier data to the newborn’s parents is necessary remains controversial.

At the same time, the current research showed no correlation between genetic variation and SGA infants. This may require further clinical and genetic analyses. Traditional screening methods have low specificity and sensitivity, making it difficult to identify genetic and metabolic diseases. However, the specificity and sensitivity of gene screening have been significantly improved, which could markedly decrease false positives, fundamentally solving the limitations of traditional screening methods, and promote the healthy development of children. The current study also had the following limitation: the sample size was statistically insufficient, and in-depth research is needed.

In conclusion, positive neonatal diseases missed by NBS with TMS and disease-related mutated gene carriers were identified in this study by Angel Care GS, providing a more effective method for disease screening in SGA which need further and more studies. In addition, Angel Care GS may be beneficial for long-term health care of SGA infants.