Letter to the editor: How many X-linked genes for non-specific mental retardation (MRX) are there?

Identification and Characterization of proSAAS, a Granin-Like Neuroendocrine Peptide Precursor that Inhibits Prohormone Processing

“…The genomic position of human proSAAS on chromosome X maps within regions associated with several different X-linked mental retardation syndromes (Gedeon et al, 1994;Stevenson et al, 1998). In addition, a susceptibility haplotype for insulindependent diabetes mellitus has been mapped to chromosome Xp13-11, which contains the proSAAS locus (Cucca et al, 1998).…”

Deletion including the oligophrenin-1 gene associated with enlarged cerebral ventricles, cerebellar hypoplasia, seizures and ataxia

“…The number of distinct genes behind this phenotype is unknown but it may be in the range of 10-50. 1 Although several genes involved in syndromic X-linked mental retardation have been identified, eg the fragile-X syndrome, only three genes associated with non-specific mental retardation have been identified: the FMR2 gene, 2 the GDI1 gene, 3 and the oligophrenin-1 gene. 4 The oligophrenin-1 gene was identified from the molecular characterisation of an X-chromosomal breakpoint (Xq12) in a female with mental retardation and an X;12 balanced translocation.…”

MEHMO (mental retardation, epileptic seizures, hypogonadism and -genitalism, microcephaly, obesity), a novel syndrome: assignment of disease locus to Xp21.1–p22.13

“…1 To date more than 30 MRX loci have been described based on linkage with lod scores of > 2.0 in different families. 2,3,4 The second category includes the fragile X (fraXA) 5 and the fraXE 6 syndromes. The third group comprises syndromic XLMR, ie MR syndromes with additional clinical features such as neurological and metabolic symptoms, auditory problems, and dysmorphological stigmata.…”