Hypomorphic temperature-sensitive alleles of NSDHL cause CK syndrome.

CK syndrome (CKS) is an X-linked recessive intellectual disability syndrome characterized by dysmorphism, cortical brain malformations, and an asthenic build. Through an X chromosome single-nucleotide variant scan in the first reported family, we identified linkage to a 5 Mb region on Xq28. Sequencing of this region detected a segregating 3 bp deletion (c.696_698del [p.Lys232del]) in exon 7 of NAD(P) dependent steroid dehydrogenase-like (NSDHL), a gene that encodes an enzyme in the cholesterol biosynthesis pathway. We also found that males with intellectual disability in another reported family with an NSDHL mutation (c.1098 dup [p.Arg367SerfsX33]) have CKS. These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast. As described for the allelic disorder CHILD syndrome, cells and cerebrospinal fluid from CKS patients have increased methyl sterol levels. We hypothesize that methyl sterol accumulation, not only cholesterol deficiency, causes CKS, given that cerebrospinal fluid cholesterol, plasma cholesterol, and plasma 24S-hydroxycholesterol levels are normal in males with CKS. In summary, CKS expands the spectrum of cholesterol-related disorders and insight into the role of cholesterol in human development.

Characterization of a new X-linked mental retardation syndrome with microcephaly, cortical malformation, and thin habitus.

X-linked mental retardation (XLMR) affects 1-2/1,000 males and accounts for approximately 10% of all mental retardation (MR). We have ascertained a syndromic form of XLMR segregating within a five-generation family with seven affected males. Prominent characteristics include mild to severe MR, cortical malformation, microcephaly, seizures, thin build with distinct facial features including a long and thin face, epicanthic folds, almond-shaped eyes, upslanting palpebral fissures and micrognathia and behavioral problems. Carrier females have normal physical appearance and intelligence. This combination of features is unreported and distinct from Lujan-Fryns syndrome, Snyder-Robinson syndrome, and zinc finger DHHC domain-containing 9-associated MR. We propose the name of this new syndrome to be CK syndrome.

HDAC inhibitors dysregulate neural stem cell activity in the postnatal mouse brain.

The mammalian central nervous system (CNS) undergoes significant expansion postnatally, producing astrocytes, oligodendrocytes and inhibitory neurons to modulate the activity of neural circuits. This is coincident in humans with the emergence of pediatric epilepsy, a condition commonly treated with valproate/valproic acid (VPA), a potent inhibitor of histone deacetylases (HDACs). The sequential activity of specific HDACs, however, may be essential for the differentiation of distinct subpopulations of neurons and glia. Here, we show that different subsets of CNS neural stem cells (NSCs) and progenitors switch expression of HDAC1 and HDAC2 as they commit to a neurogenic lineage in the subventricular zone (SVZ) and dentate gyrus (DG). The administration of VPA for only one week from P7-P14, combined with sequential injections of thymidine analogs reveals that VPA stimulates a significant and differential decrease in the production and differentiation of progeny of NSCs in the DG, rostral migratory stream (RMS), and olfactory bulb (OB). Cross-fostering VPA-treated mice revealed, however, that a postnatal failure to thrive induced by VPA treatment had a greater effect on DG neurogenesis than VPA action directly. By one month after VPA, OB interneuron genesis was significantly and differentially reduced in both periglomerular and granule neurons. Using neurosphere assays to test if VPA directly regulates NSC activity, we found that short term treatment with VPA in vivo reduced neurosphere numbers and size, a phenotype that was also obtained in neurospheres from control mice treated with VPA and an alternative HDAC inhibitor, Trichostatin A (TSA) at 0 and 3 days in vitro (DIV). Collectively, these data show that clinically used HDAC inhibitors like VPA and TSA can perturb postnatal neurogenesis; and their use should be carefully considered, especially in individuals whose brains are actively undergoing key postnatal time windows of development.