PPP2R2C, a gene disrupted in autosomal dominant intellectual disability.

Intellectual disability (ID) comprises a vast collection of clinically diverse and genetically heterogeneous disorders characterized primarily by central nervous system defects of varying severity with or without additional dysmorphic, metabolic, neuromuscular or psychiatric features. Much progress has been made to elucidate the genetic causes for ID, especially on the X-chromosome. In order to identify autosomal genes involved in ID, patients with a balanced chromosomal rearrangement are a valuable source since the breakpoints may disrupt or deregulate a candidate ID gene(s). Here, we report a familial reciprocal translocation (4;6)(p16.1;q22) that segregates with mild ID, epilepsy and behavioural problems and that disrupts the PPP2R2C gene on chromosome 4p. The PPP2R2C gene, encoding a subunit of protein phosphatase 2A, has a unique expression pattern in mouse brain that suggests a role in synaptic plasticity and hence learning and memory.

Dosage-dependent severity of the phenotype in patients with mental retardation due to a recurrent copy-number gain at Xq28 mediated by an unusual recombination.

We report on the identification of a 0.3 Mb inherited recurrent but variable copy-number gain at Xq28 in affected males of four unrelated families with X-linked mental retardation (MR). All aberrations segregate with the disease in the families, and the carrier mothers show nonrandom X chromosome inactivation. Tiling Xq28-region-specific oligo array revealed that all aberrations start at the beginning of the low copy repeat LCR-K1, at position 153.20 Mb, and end just distal to LCR-L2, at 153.54 Mb. The copy-number gain always includes 18 annotated genes, of which RPL10, ATP6AP1 and GDI1 are highly expressed in brain. From these, GDI1 is the most likely candidate gene. Its copy number correlates with the severity of clinical features, because it is duplicated in one family with nonsyndromic moderate MR, is triplicated in males from two families with mild MR and additional features, and is present in five copies in a fourth family with a severe syndromic form of MR. Moreover, expression analysis revealed copy-number-dependent increased mRNA levels in affected patients compared to control individuals. Interestingly, analysis of the breakpoint regions suggests a recombination mechanism that involves two adjacent but different sets of low copy repeats. Taken together, our data strongly suggest that an increased expression of GDI1 results in impaired cognition in a dosage-dependent manner. Moreover, these data also imply that a copy-number gain of an individual gene present in the larger genomic aberration that leads to the severe MECP2 duplication syndrome can of itself result in a clinical phenotype as well.

Congenital diaphragmatic hernia is part of the new 15q24 microdeletion syndrome.

The recurrent microdeletion 15q24 syndrome is rare with only 5 cases reported thus far. Here we describe an additional patient with this deletion, presenting with many features common to this syndrome, including developmental delay, loose connective tissue, digital and genital anomalies and a distinct facial gestalt. Interestingly, in addition, this patient has a large congenital diaphragmatic hernia, as was described in one other patient with a 15q24 microdeletion, indicating that this feature might be part of the syndrome. Chromosome 15q24 has a highly polymorphic architecture that is prone to genomic rearrangements underlying this novel microdeletion syndrome.