Pilch et al recently reported that mutations in HNRNPH1 may cause Bain type syndromic mental retardation (MRXSB) in boys. 1 So far, this syndrome has been only described in females caused by de novo mutations in the X-linked HNRNPH2 gene. 2 It was thought that the disease is embryonic lethal in hemizygous males. Pilch et al. postulated that malfunction of HNRNPH1 and HNRNPH2 may have similar clinical consequences as both paralogues are highly conserved especially in the nuclear localization sequence (NLS), which is affected by all mutations reported so far for both genes. 1 However, they pointed out that due to the autosomal localization of the HNRNPH1 gene this type of MRXSB may also occur in male individuals.

Here, we describe a boy with MRXSB caused by a hemizygous de novo mutation in the HNRNPH2 gene. The patient is the second child of healthy non-consanguineous parents from Romania. He was born at term without complications (weight 3.920 g [P 75], length 52 cm [P 41], head circumference 36 cm [P 62], Apgar-score 10/10). During the first year of life muscular hypotonia and profound developmental delay became evident. Diagnostic work-up did not reveal the etiology of his neurocognitive disorder. It included brain MRI/MR spectroscopy, electroencephalography, brain evoked response audiometry, clinical chemistry and metabolic investigations (amino acids in plasma, acylcarnitines, purines and pyrimidines as well as organic acids in urine, lysosomal enzymes in blood, glycosaminoglycans and oligosaccharides in urine, very-long-chain fatty acids in plasma, transferrin