We reviewed studies that reported results of systematic cytomegalovirus (CMV) screening on fetuses and/or live-born infants. The overall birth prevalence of congenital CMV infection was 0.64%, but varied considerably among different study populations. About 11% of live-born infants with congenital CMV infection were symptomatic, but the inter-study differences in definitions of symptomatic cases limit the interpretation of these data. Non-white race, low socioeconomic status (SES), premature birth, and neonatal intensive care unit admittance were risk factors for congenital CMV infection. Birth prevalence increased with maternal CMV seroprevalence. Maternal seroprevalence accounted for 29% of the variance in birth prevalence between study populations. Maternal seroprevalence and birth prevalence were both higher in study populations that were ascertained at birth rather than in the prenatal period. Thus, timing of ascertainment should be considered when interpreting birth prevalence estimates. Birth prevalence was inversely correlated with mean maternal age, but this relationship was not significant when controlling for maternal seroprevalence. The rate of transmission to infants born to mothers who had a primary infection or a recurrent infection during pregnancy was 32% and 1.4%, respectively. Possible maternal primary infections (i.e. seropositive mother with CMV IgM) resulted in congenital infections about 20% of the time, but are likely to represent a mixture of primary and recurrent infections. In summary, CMV is a common congenital infection worldwide that can lead to permanent disabilities. There is an urgent need for interventions that can reduce the substantial burden of this often overlooked disease.

The 5' untranslated CGG repeat in the fragile X mental retardation-1 (FMR1) gene is expanded in families with fragile X syndrome, with more than 200 CGGs resulting in mental retardation due to the absence of the encoded fragile X mental retardation protein (FMRP). Intermediate and premutation alleles, containing between approximately 40 and 200 repeats, express grossly normal FMRP levels and such carriers are widely believed to be non-penetrant, despite continued reports of subtle cognitive/psychosocial impairment and other phenotypes. Using a highly sensitive quantification assay, we demonstrate significantly diminished FMRP levels in carriers, negatively correlated with repeat number. Despite reduced FMRP, these carrier alleles overexpress FMR1, resulting in a positive correlation between repeat number and FMR1 message level. These biochemical deviations associated with intermediate and premutation FMR1 alleles, found in approximately 4% of the population, suggest that the phenotypic spectrum of fragile X syndrome may need to be revisited.

Despite the enormous heterogeneity of genetic hearing loss, variants in one locus, Gap Junction Beta 2 or GJB2 (connexin 26), account for up to 50% of cases of nonsyndromic sensorineural hearing loss in some populations. This article reviews genetic epidemiology studies of the alleles of GJB2, prevalence rates, genotype-phenotype relations, contribution to the incidence of hearing loss, and other issues related to the clinical validity of genetic testing for GJB2. This review focuses primarily on three alleles: 167⌬T, 35⌬G, and 235⌬C. These alleles are recessive for nonsyndromic prelingual sensorineural hearing loss, and the evidence suggests complete penetrance but variable expressivity. GENEThe Gap Junction Beta 2 or GJB2 gene (GenBank M86849, OMIM: *121011) resides at the chromosomal location 13q11 and encodes for the protein connexin 26, a beta class gap junction protein expressed in the cochlea and in the epidermis. 3 Connexin 26 hexamers form channels between cells that, when open, allow cell-to-cell diffusion of small molecules. This function is necessary for recycling potassium in the cochlea that plays a critical role in sensorineural hearing function. 4 The GJB2 gene is small, with the entire coding region of 680 base pairs falling within exon 2. GENE VARIANTSAided by the relatively small size of the GJB2 gene, the flourish of activity on the genetics of hearing loss has resulted in rapid identification of GJB2 variants. Missense, nonsense, frameshift, insertion, and deletion variants have all been reported. To identify published genetic epidemiology studies related to GJB2, we searched the MEDLINE database using the keywords GJB2, connexin 26, and hearing loss to identify relevant studies. References in related studies were also reviewed.A list of GJB2 variants is presented in Table 1. Some variants are benign polymorphisms, with a high prevalence rate in various populations. For example, the V27I, E114G, and I203T variants were found on 54%, 55%, and 94% of Japanese chromosomes, respectively. 5,6 The 167⌬T, 35⌬G (also known as 30⌬G), 235⌬C, and R143W alleles are the most common hearing loss-associated GJB2 alleles in the Ashkenazi Jewish, Caucasian, Japanese, and Ghanian populations, respectively. The best-characterized population is Caucasian of northern European descent. Table 2 presents the heterozygote carrier frequencies of the first three alleles either in the general population (hearing status unknown) or in control groups (without hearing loss). Ascertainment details were generally lacking and are listed in Table 2 as described in the publication. Likewise, descriptive information, including sex and age, were generally not provided. Despite these limitations, the studies consistently reported a prevalence of the 35⌬G allele in the range of 1% to 3%. In fact, one population-based study, which genotyped 560 randomly selected neonatal bloodspots in the Midwestern United States, detected a 35⌬G heterozygosity rate of 2.5% in this predominantly Caucasian population. 7 In addition to Caucasians, ...