Novel mutation in TSPAN12 leads to autosomal recessive inheritance of congenital vitreoretinal disease with intra-familial phenotypic variability.

Developmental malformations of the vitreoretinal vasculature are a heterogeneous group of conditions with various modes of inheritance, and include familial exudative vitreoretinopathy (FEVR), persistent fetal vasculature (PFV), and Norrie disease. We investigated a large consanguineous kindred with multiple affected individuals exhibiting variable phenotypes of abnormal vitreoretinal vasculature, consistent with the three above-mentioned conditions and compatible with autosomal recessive inheritance. Exome sequencing identified a novel c.542G > T (p.C181F) apparently mutation in the TSPAN12 gene that segregated with the ocular disease in the family. The TSPAN12 gene was previously reported to cause dominant and recessive FEVR, but has not yet been associated with other vitreoretinal manifestations. The intra-familial clinical variability caused by a single mutation in the TSPAN12 gene underscores the complicated phenotype-genotype correlation of mutations in this gene, and suggests that there are additional genetic and environmental factors involved in the complex process of ocular vascularization during embryonic development. Our study supports considering PFV, FEVR, and Norrie disease a spectrum of disorders, with clinical and genetic overlap, caused by mutations in distinct genes acting in the Norrin/ß-catenin signaling pathway.

Can auxology, IGF-I and IGFBP-3 measurements followed by MRI and genetic tests replace GH stimulation tests in the diagnosis of GH deficiency in children?

BACKGROUND/AIMS: GH levels < 10 ng/ml in response to two different GH stimulation tests (GHSTs) are traditionally used to identify children with GH deficiency (GHD). Since GHSTs are imprecise, other diagnostic tools have been proposed. We assessed whether auxology, IGF-I and IGFBP-3 measurements followed by brain MRI and genetic analysis can replace the current diagnostic approach. METHODS: Fifty-three children diagnosed with GHD by two different GHSTs. GH-1 gene was sequenced. RESULTS: At presentation, 17% of patients were with height above -1.5 SD and 28% above -2.0 SD; 50% had IGF-1 concentration above -1.5 SD and 58% above -2.0 SD; 59% had pituitary anomalies demonstrated by MRI. Fourteen patients harbored the heterozygous R183H mutation, one patient had the N47D mutation and one had a novel F25Y mutation in GH-1. Using cut-off levels of -1.5 SD for height, IGF-I and IGFBP-3 excluded the diagnosis of GHD in 17, 68 and 79% of the children, respectively; a cut-off of -2 SD excluded 28, 88 and 96%, respectively. Further brain MRI and genetic tests excluded 81-96% and 96-100%, respectively, of children currently diagnosed with GH. CONCLUSION: Use of the tested approach, which avoids carrying out two GHSTs, would exclude most children currently diagnosed with GHD. Until better tools become available, we recommend identifying GHD in children by an integrated approach combining phenotype, auxological parameters, hormonal measurements and two separate GHSTs, with MRI and genetic tests to support the diagnosis.

Myotonia congenita in a large consanguineous Arab family: insight into the clinical spectrum of carriers and double heterozygotes of a novel mutation in the chloride channel CLCN1 gene.

The aims of this study were to (1) characterize the clinical phenotype, (2) define the causative mutation, and (3) correlate the clinical phenotype with genotype in a large consanguineous Arab family with myotonia congenita. Twenty-four family members from three generations were interviewed and examined. Genomic DNA was extracted from peripheral blood samples for sequencing the exons of the CLCN1 gene. Twelve individuals with myotonia congenita transmitted the condition in an autosomal dominant manner with incomplete penetrance. A novel missense mutation [568GG>TC (G190S)] was found in a dose-dependent clinical phenotype. Although heterozygous individuals were asymptomatic or mildly affected, the homozygous individuals were severely affected. The mutation is a glycine-to-serine residue substitution in a well-conserved motif in helix D of the CLC-1 chloride channel in the skeletal muscle plasmalemma. A novel mutation, 568GG>TC (G190S) in the CLCN1 gene, is responsible for autosomal dominant myotonia congenita with a variable phenotypic spectrum.

Mutated NDUFS6 is the cause of fatal neonatal lactic acidemia in Caucasus Jews.

NADH:ubiquinone oxidoreductase (complex I; EC 1.6.5.3), the largest respiratory chain complex is composed of 45 proteins and is located at the mitochondrial inner membrane. Defects in complex I are associated with energy generation disorders, of which the most severe is congenital lactic acidosis. We report on four infants from two unrelated families of Jewish Caucasus origin with fatal neonatal lactic acidemia due to isolated complex I deficiency. Whole genome homozygosity mapping, identified a 2.6 Mb region of identical haplotype in the affected babies. Sequence analysis of the nuclear gene encoding for the NDUFS6 mitochondrial complex I subunit located within this region identified the c.344G>A homozygous mutation resulting in substitution of a highly evolutionary conserved cysteine residue by tyrosine. This is the second report of NDUFS6 mutation in humans. Both reports describe three diverse homozygous mutations with variable consequential NDUFS6 protein defects that result in similar phenotype. Our study further emphasizes that NDUFS6 sequence should be analyzed in patients presenting with lethal neonatal lactic acidemia due to isolated complex I deficiency.

Genetic heterogeneity in two consanguineous families segregating early onset retinal degeneration: the pitfalls of homozygosity mapping.

Retinitis pigmentosa is the most common form of hereditary retinal degeneration, with a worldwide prevalence of 1 in 4,000. At least 28 genes and loci have been implicated in nonsyndromic autosomal recessive retinitis pigmentosa. Here we report two extended and highly consanguineous families segregating early onset retinitis pigmentosa. Despite the consanguinity in both families, we found allelic heterogeneity in one of them, in which affected individuals were compound heterozygotes for two different mutations of the CRB1 gene. In the second family we found evidence for locus heterogeneity. A novel homozygous mutation of RDH12 was found in only 14 of 17 affected individuals in this family. Our data indicate that in the other affected individuals the disease is caused by a different gene/s. These findings demonstrate that while homozygosity mapping is an efficient tool for identification of the underlying mutated genes in inbred families, both locus and allelic heterogeneity may occur even within the same consanguineous family. These observations should be taken into account, especially when studying common and heterogeneous recessive genetic conditions.

Variable phenotypes in familial isolated growth hormone deficiency caused by a G6664A mutation in the GH-1 gene.

CONTEXT: G to A transition at position 6,664 (G6664A) in human GH-1 results in the substitution of arginine by histidine at position 183 (R183H) of the GH molecule and causes familial isolated GH deficiency type II (IGHD II). OBJECTIVES: The objective of the study was to assess the phenotype-genotype correlation of subjects affected with IGHD II caused by a G6664A mutation in 34 affected members of two large families. DESIGN AND PATIENTS: Sixty-six subjects from two core families were included. The G6664A mutation among family members was determined by restriction fragment length polymorphism. RESULTS: Twenty-four of the 52 members from family 1 and 10 of 14 from family 2 carried the same G6664A mutation in a heterozygous state. The affected subjects in family 1 were significantly shorter [-2.6 vs. -0.1 sd score (SDS), P < 0.0001] and had significantly lower IGF-I serum levels (-1.9 vs. -0.5 SDS, P < 0.0001), compared with normal-genotype family members. The affected adults exhibited great variability in their stature, ranging from -4.5 to -1.0 (mean -2.8 SDS), with five members being of normal height (>-2 SDS). Twelve children were diagnosed with IGHD. Two affected children had normal peak GH levels, although one of these subsequently demonstrated GH insufficiency (6.5 and 3.7 ng/ml). The affected children from both families exhibited large variability in their height, growth velocity, delay in bone age (chronological age - bone age), age at diagnosis, peak GH response, and IGF-I levels. CONCLUSIONS: These detailed phenotypic analyses show the variable expressivity of patients bearing a G6664A mutation, reflecting the spectrum of GH deficiency in affected patients, even within families, and the presence of additional genes modifying height determination. Our findings raise a new dilemma in the guidelines for the diagnosis of GH deficiency and the indications for GH therapy.

Growth hormone receptor sequence changes do not play a role in determining height in children with idiopathic short stature.

BACKGROUND/AIMS: In children with short stature, in whom growth hormone deficiency has been excluded, the presence of a normal or elevated growth hormone concentration concomitant with low insulin-like growth factor I suggests growth hormone insensitivity (GHI). Previous reports suggest that heterozygous mutations in the growth hormone receptor gene (GHR) may account for about 5% of children with idiopathic short stature (ISS). In the present study we have attempted to determine whether mutations in the GHR explain the short stature and growth retardation in a cohort of children with ISS and characteristics suggesting GHI. METHODS: For the present study 33 children with clinical and biochemical characteristics of GHI were selected from a cohort of 150 children of short stature. Molecular analysis of the GHR was performed using a single-strand conformation polymorphism technique and sequencing. Ten different sequence changes in 19 (58%) out of 33 children were identified, 9 of them novel and 1 that had been described previously. RESULTS: Two changes were found in exons 2 and 6. The known polymorphism of exon 6 (G168) was significantly more common in the control subjects than in our study group (63.5 vs. 30%; p < 0.0001). In the intronic sequences 8 previously undescribed DNA changes were found. The screening of the affected children's family members revealed that both normal and short stature members carried the same variants. The study group did not significantly differ from the controls in retention (GHRfl) or exclusion (GHRd3) of exon 3. CONCLUSION: Our study suggests that sequence changes of the GHR are common in children with ISS. The presence of these sequence changes in the control subjects as well as in normal stature family members indicates that these changes represent a simple polymorphism of the GHR. Such DNA changes are more prevalent than previously recognized, and they do not seem to play a contributory role in the etiology of short stature.