Characterization of patients referred for non-specific intellectual disability testing: the importance of autosomal genes for diagnosis.

Genetic testing for non-specific intellectual disability (ID) presents challenges in daily clinical practice. Historically, the focus of the genetic elucidation of non-specific ID has been on genes on the X chromosome, and recent research has brought attention to the growing contribution of autosomal genes. In addition, next-generation sequencing (NGS) has greatly improved the ability to simultaneously analyze multiple genetic loci, making large panel testing a practical approach to testing for non-specific ID. We performed NGS analysis of a total of 90 genes implicated in non-specific ID. The 90 genes included 56 X-linked genes and 34 autosomal genes. Pathogenic variants were identified in 11 of 52 (21%) patient samples. Nine of the eleven cases harbored mutations in autosomal genes including AP4B1, STXB1, SYNGAP1, TCF4 and UBE3A. Our mutation-positive cases provide further evidence supporting the prevalence of autosomal mutations in patients referred for non-specific ID testing and the utility of their inclusion in multi-gene panel analysis.

Deletion of MAP2K2/MEK2: a novel mechanism for a RASopathy?

RASopathies are a class of genetic syndromes caused by germline mutations in genes encoding Ras/mitogen-activated protein kinase (Ras/MAPK) pathway components. Cardio-facio-cutaneous (CFC) syndrome is a RASopathy characterized by distinctive craniofacial features, skin and hair abnormalities, and congenital heart defects caused by activating mutations of BRAF, MEK1, MEK2, and KRAS. We define the phenotype of seven patients with de novo deletions of chromosome 19p13.3 including MEK2; they present with a distinct phenotype but have overlapping features with CFC syndrome. Phenotypic features of all seven patients include tall forehead, thick nasal tip, underdeveloped cheekbones, long midface, sinuous upper vermilion border, tall chin, angular jaw, and facial asymmetry. Patients also have developmental delay, hypotonia, heart abnormalities, failure to thrive, obstructive sleep apnea, gastroesophageal reflux and integument abnormalities. Analysis of epidermal growth factor-stimulated fibroblasts revealed that P-MEK1/2 was ∼50% less abundant in cells carrying the MEK2 deletion compared to the control. Significant differences in total MEK2 and Sprouty1 abundance were also observed. Our cohort of seven individuals with MEK2 deletions has overlapping features associated with RASopathies. This is the first report suggesting that, in addition to activating mutations, MEK2 haploinsufficiency can lead to dysregulation of the MAPK pathway.

Distal deletion of chromosome 1q in an adult.

An adult patient with mongoloid appearance, profound retardation and autistic-like behavior was found to have a deletion of the distal bands of chromosome 1q. To our knowledge, this is the oldest patient with distal deletion 1q.

Autosomal recessive Duane's retraction syndrome.

The first two cases of probable autosomal recessive Duane's retraction syndrome, in two siblings, are reported.

Norrie's disease in a French-Canadian kindred: attempt to detect carriers by DNA analysis.

In a French-Canadian kindred four male cousins are affected with Norrie's disease, a rare X-linked recessive disorder. Three have university education, and the fourth has some developmental delay. Only one is microcephalic. All have mild to severe hearing deficit, although only three were aware of their hearing loss. Linkage analysis of DNA from family members with the probe L1.28 failed to detect female carriers.

Folic acid blinded trial in identical twins with fragile X syndrome.

Monozygous twin 14-year-old mentally retarded boys with the fragile X syndrome were treated either with 10 mg folic acid by mouth daily or with a placebo for three test periods of 3-month duration each in a blind study. For each twin, tests of cognitive functioning, reading, spelling, and math skills, and linguistic and perceptual skills were compared. Although there was considerable variation in performance on these tests during the two baseline periods, there were no observable beneficial effects of therapy. The routine use of folic acid in patients with established mental retardation and the fragile X syndrome is not indicated.

A private view of heterozygosity: eight-year follow-up study on carriers of the Tay-Sachs gene detected by high school screening in Montreal.

We surveyed 264 persons (132 carriers, 132 matched noncarriers) screened for Tay-Sachs heterozygosity during 1974-76 in a program directed at senior high school students in Montreal. Among 198 who apparently received the questionnaire in 1982, the response rate was 42% (38 carriers, 45 noncarriers; age range 21-26 yr). Respondents and nonrespondents had no apparent demographic differences. Of eight unable to remember their genotype only one was a carrier (these persons were excluded from the study). The subjects were: single (75%), married (20%), engaged (3%), divorced (1%); 32% of carriers were engaged or married vs 16% of noncarriers. (There were no carrier couples in our sample, but one such couple, who married after being screened in the high school program, requested amniocentesis in 1981.) Only three of the 12 spouses or fiancé(s) of carriers have not been tested (vs 3 of 6 noncarrier partners). Only 19% of carriers now attach any "worry" to heterozygosity (vs 46% at the earlier time of test disclosure, P = 0.001); carriers with spouses or fiancé(e)s are less "worried" than unattached carriers. Only 3% of carriers claim they would change marriage plans if their fiancé(e) was also a carrier. Carriers and noncarriers uniformly approve (96%) genetic screening for themselves and for other mutant genotypes; 92% of carriers and 95% of noncarriers approve being screened in high school. These findings indicate that Canadians screened in high school: 1) have largely positive attitudes toward genetic screening long after the experience, and 2) are making appropriate use of the test result.