A novel homozygous mutation p.E88K in maternal SLC30A2 gene as a cause of transient neonatal zinc deficiency

The SLC30A2 gene encodes zinc transporter ZnT2, which is indispensable for the transport of zinc into the breast milk in the mammary gland. Transient neonatal zinc deficiency (TNZD) is caused by a mutation in the maternal SLC30A2 gene and has a clinical presentation similar to that of acrodermatitis enteropathica (AE). We described the case of a Chinese infant who presented with AE-like lesions 10 days after birth. Sanger sequencing of the AE-causing gene SLC39A4 revealed no mutations in genomic DNA from the infant, excluding the possibility of AE. Detection of the mother's breast milk showed a significantly lower zinc level. Thus, SLC30A2 sequencing was performed on her genomic DNA and a previously unreported homozygous c.262G > A (p.E88K) mutation was disclosed. Functional analysis suggested the novel mutation could lead to a strong disruption of zinc secretion, which indicated a complete loss of function in the ZnT2 protein. We finally diagnosed the infant with TNZD. To the best of our knowledge, this is the first case of TNZD caused by a homozygous mutation in the maternal SLC30A2 gene. Compared to the heterozygous condition, a homozygous mutation seems to result in a more significant decrease in zinc secretion and a more rapid onset of TNZD.