S.), ALS Association (R.S.), the Johns Hopkins Brain Science Institute, The Ansari ALS Center for Cell Therapy and Regeneration Research at Johns Hopkins, The Alzheimer Drug Discovery Foundation and the Association for Frontotemporal Degeneration, The Finnish Academy, The Sigrid Juselius Foundation, the Helsinki University Central Hospital, Robert Packard Center for ALS Research, Maryland Stem Cell Research

Fund (C.J.D.), Intramural Research Programs of the US National Institutes of Health (NIH) (B.T.), and National Institute on Aging (B.T.). We would like to thank the Johns Hopkins Deep Sequencing and Microarray Core PLX3397 solubility dmso for the valuable insight on high-throughput experimental design and analysis. Dr. Phillip Wong provided data analysis and interpretation. Dr. Lyle Ostrow provided human tissue demographics. Additional technical and reagent support was graciously provided by Meredith Davitt, Uma Balasubramanian, Conover Talbot Jr., Dr. Tania Gendron, and Dr. Jean-Phillipe Richard. J.D.R, R.S., C.J.D., F.R., and C.F.B. have patents pending on antisense therapeutics and associated genetic biomarkers. B.T. has patents pending for the diagnostic and therapeutic uses of the C9ORF72 hexanucleotide repeat expansion. The remaining authors

have no competing financial interests. “
“Intellectual find more disability (ID) affects 2%–3% of the general population and is characterized by a broad range of cognitive deficits. It is usually subdivided into syndromic and nonsyndromic forms, depending on whether additional abnormalities are found. Syndromic ID is often accompanied by microcephaly, defined by a head circumference more before than two SDs below the age- and sex-adjusted mean. The incidence of microcephaly, as reported in birth

defect registries world-wide, varies from 1 to 150 per 100,000 depending upon the range of SD used to define microcephaly and the ethnic population. For example, microcephaly is more prevalent in populations with a high degree of consanguinity (Mahmood et al., 2011). Causes of congenital microcephaly include metabolic disorders, chromosomal anomalies, and intrauterine infections. However, with the exception of autosomal recessive primary microcephaly (MCPH), the genetic etiology of most congenital microcephaly cases is unknown. We ascertained four families with a distinct form of severe encephalopathy associated with congenital microcephaly and progressive brain atrophy. Two families were from the same ethnic group, whereas the other two families were independently recognized as presenting with an identical syndrome. Both pairs of families were analyzed independently by exome sequencing. Here we report the clinical features of the affected children and demonstrate that the observed phenotype in all four families can be explained by autosomal recessive deficiency of asparagine synthetase (ASNS).