Nolan et al. (2008) described a large consanguineous Hutterite family, originally identified by Ober et al. (2001), with autosomal recessive nonsyndromic mental ...
Nolan et al. (2008) described a large consanguineous Hutterite family, originally identified by Ober et al. (2001), with autosomal recessive nonsyndromic mental retardation. The family included 2 sisters, aged 32 and 47 years, and 2 brothers, aged 40 and 49 years, with mild to moderate mental retardation. The remaining 9 sibs and their parents were intellectually normal. The 4 affected sibs had developmental delay since birth, communicated verbally but had speech delays, and could read and write their names but otherwise had minimal reading or writing skills. They were unable to live independently as adults, performed jobs requiring manual labor, but were unable to perform tasks requiring fine motor skills. Growth parameters, including head circumference, were normal. There were no dysmorphic features other than a narrow palate in the 3 individuals examined. Their neurologic exams were unremarkable except for an initiation tremor when asked to do finger-nose-finger exam or any other task requiring fine motor coordination.
In a Hutterite family with autosomal recessive nonsyndromic mental retardation, Nolan et al. (2008) demonstrated linkage to chromosome 19p13 (lod score 1.2-3.5, depending on assumptions of allele frequencies). The pedigree that contained all of the common ancestors of the parents was too large and complex for linkage programs that use exact calculations. Fine mapping defined a critical region of 3.6 Mb, which overlapped a gene previously implicated in mental retardation (CC2D1A; 610055); however, no mutations in the coding region of CC2D1A were found. The authors suggested that another gene causing autosomal recessive nonsyndromic mental retardation was located within this genomic region.
▼ Molecular Genetics
Caliskan et al. (2011) performed exome sequencing of the 4 affected individuals described by Nolan et al. (2008) as well as of another sib whose mild developmental delay had been attributed to birth trauma and infection and who had not been considered affected by Nolan et al. (2008). All 5 sibs were homozygous for a pro182-to-leu substitution in trans-2,3-enoyl-CoA reductase (610057.0001), a synaptic glycoprotein.
Among 1,496 Schmiedeleut (S-leut) Hutterites from the United States, Chong et al. (2012) found 103 heterozygotes and 5 homozygotes for the P182L mutation in the TECR gene (rs199469705), for a frequency of 0.069, or 1 in 14.5. This is a private mutation in the Hutterite population.