A clinical and genetic overview of 18 years neurofibromatosis type 1 molecular diagnostics in the Netherlands.

NF1 mutations are the underlying cause of neurofibromatosis type 1 (NF1), a neuro-cardio-facio-cutaneous syndrome (NCFC). Because of the clinical overlap between NCFCs, genetic analysis of NF1 is necessary to confirm a clinical diagnosis NF1. This report describes the clinical and genetic findings of 18 years of NF1 molecular diagnostics in the Netherlands. A pathogenic mutation was found in 59.3% (1178/1985) of the index patients, mostly de novo (73.8%). The majority of the index patients (64.3%) fulfilled the National Institute of Health NF1 criteria, a pathogenic mutation was found in 80.9% of these patients. Seventy-four percent of the index patients with an NF1 pathogenic mutation and not fulfilling the NF1 criteria is <12 years, in agreement with the fact that some NF1 symptoms appear after puberty. Genotype-phenotype correlations were studied for 527 index patients. NF1 patients with a type 1 microdeletion have a sixfold higher risk of special education vs NF1 patients with an intragenic mutation. No evidently milder NF1 phenotype for patients with a missense mutation was observed. Forty-six prenatal analyses were performed in 28 (2.4%) families, of which 29 (63%) showed heterozygosity for the familial pathogenic mutation. This indicates that there is a need for prenatal NF1 testing.

Considering Fabry, but Diagnosing MPS I: Difficulties in the Diagnostic Process.

INTRODUCTION: Recent studies have indicated that a proportion of patients with renal failure, left ventricular hypertrophy, or cryptogenic stroke have sequence variants in their aGal A gene (Fabry disease), which has resulted in an increase in diagnostic activities for this disorder. The diagnostic process for lysosomal storage disorders may result in findings of unknown clinical significance. Here we report such an unexpected outcome. CASE: A 32-year-old male presented at the emergency department because of a transient ischemic attack. Extensive investigations revealed no cause and an initial diagnosis of cryptogenic stroke was made. Subsequently, aGal A activity was measured in a bloodspot and was shown to be normal, but the activity of alpha-L-iduronidase (IDUA), used as reference enzyme, was unexpectedly low: 0.5 umol/L (ref = 1.7-14.3). A diagnosis of IDUA deficiency, mucopolysaccharidosis type 1S or Scheie disease was considered. IDUA gene analysis revealed two homozygous sequence alterations: a silent sequence change (979C > T) in exon 7 (N297N) and an unknown missense mutation 875A > T (R263W). Physical examination was completely normal, without clinical signs of mucopolysaccharidosis type I (MPS I). Leukocyte IDUA activity was also low: 2.1 nmol/mg prot/h (ref = 14-40 nmol prot/h), but higher than the patient range of <0.1 nmol/mg prot/h. Urinary glycosaminoglycan levels were normal both quantitatively and qualitatively. It was concluded that there was low IDUA activity without clinical symptoms and the diagnosis of mucopolysaccharidosis I was discarded. CONCLUSION: The diagnostic process for lysosomal storage disorders may result in biochemical abnormalities of unknown clinical significance. Early evaluation by a specialist in inborn errors of metabolism may help to avoid anxiety in patients and unnecessary additional analyses.

Movement disorder and neuronal migration disorder due to ARFGEF2 mutation.

We report a child with a severe choreadystonic movement disorder, bilateral periventricular nodular heterotopia (BPNH), and secondary microcephaly based on compound heterozygosity for two new ARFGEF2 mutations (c.2031_2038dup and c.3798_3802del), changing the limited knowledge about the phenotype. The brain MRI shows bilateral hyperintensity of the putamen, BPNH, and generalized atrophy. Loss of ARFGEF2 function affects vesicle trafficking, proliferation/apoptosis, and neurotransmitter receptor function. This can explain BPNH and microcephaly. We hypothesize that the movement disorder and the preferential damage to the basal ganglia, specifically to the putamen, may be caused by an increased sensitivity to degeneration, a dynamic dysfunction due to neurotransmitter receptor mislocalization or a combination of both.

Filamin A mutation, a common cause for periventricular heterotopia, aneurysms and cardiac defects.

Filamin A is an important gene involved in the development of the brain, heart, connective tissue and blood vessels. A case is presented illustrating the challenge in recognising patients with filamin A mutations. The patient, a 71-year-old woman, was known to have heart valve disease and bilateral periventricular nodular heterotopia when she died of a subarachnoid haemorrhage. Autopsy showed typical cerebral bilateral periventricular heterotopia and vascular abnormalities. Postmortally, the diagnosis of a filamin A mutation was confirmed. Recognition during life may prevent cardiovascular problems and provide possibilities for genetic counselling.

A high incidence of MSH6 mutations in Amsterdam criteria II-negative families tested in a diagnostic setting.

BACKGROUND AND AIMS: In Lynch syndrome, the clinical phenotype in MSH6 mutation families differs from that in MLH1 and MSH2 families. Therefore, MSH6 mutation families are less likely to fulfil diagnostic criteria such as the Amsterdam II criteria (AC II) and the revised Bethesda guidelines (rBG), and will be underdiagnosed. The aim of the present study was to evaluate the contribution of MSH6 gene mutations in families that were analysed for Lynch syndrome in a diagnostic setting. METHODS: Families that had molecular analysis for Lynch syndrome were included in this study. Complete molecular screening of the MLH1, MSH2 and MSH6 genes was performed in all families. Microsatellite instability (MSI) and immunohistochemical (IHC) analysis was performed in almost all families. Clinical data were collected from medical records and family pedigrees. RESULTS: A total of 108 families were included. MSI and IHC analysis was performed in 97 families, and in 40 an MSI-high phenotype with absent protein expression was found. Germline mutation analysis detected mutations in 23 families (7 MLH1, 4 MSH2 and 12 MSH6). The majority of MSH6 families were AC II negative, but fulfilled the rBG. CONCLUSIONS: There is a high incidence of MSH6 mutations in families tested for Lynch syndrome in a diagnostic setting. Many of these families remain underdiagnosed using the AC II. The rBG are more useful to select these families for further analysis. However, to optimise the detection of MSH6 families, MSI and IHC analysis should also be performed in families with clustering of late-onset endometrial carcinoma.

Frequency of Von Hippel-Lindau germline mutations in classic and non-classic Von Hippel-Lindau disease identified by DNA sequencing, Southern blot analysis and multiplex ligation-dependent probe amplification.

The current clinical diagnosis of Von Hippel-Lindau (VHL) disease demands at least one specific [corrected] VHL manifestation in a patient with familial VHL disease, or, in a [corrected] sporadic patient, at least two or more hemangioblastomas or a single hemangioblastoma in combination with a typical visceral lesion. To evaluate this definition, we studied the frequency of germline VHL mutation in three patients groups: (i) multi-organ involvement (classic VHL), (ii) limited VHL manifestations meeting criteria (non-classic VHL) and (iii) patients with VHL-associated tumors not meeting current diagnostic VHL criteria. In addition, we validated multiplex ligation-dependent probe amplification (MLPA) as a rapid and reliable quantitative method for the identification of germline VHL deletions. The frequency of germline VHL mutations was very high in classic VHL cases with multi-organ involvement (95%), lower in non-classic cases that meet current diagnostic criteria but have limited VHL manifestations or single-organ involvement (24%) and low (3.3%), but tangible in cases not meeting current diagnostic VHL criteria. The detection of germline VHL mutations in patients or families with limited VHL manifestations, or single-organ involvement is relevant for follow-up of probands and early identification of at-risk relatives.

Broad spectrum of Pompe disease in patients with the same c.-32-13T->G haplotype.

BACKGROUND: Pompe disease (acid maltase deficiency, glycogen storage disease type II; OMIM 232300) is an autosomal recessive lysosomal storage disorder characterized by acid alpha-glucosidase deficiency due to mutations in the GAA gene. Progressive skeletal muscle weakness affects motor and respiratory functions and is typical for all forms of Pompe disease. Cardiac hypertrophy is an additional fatal symptom in the classic infantile subtype. c.-32-13T-->G is the most common mutation in adults. OBJECTIVE: To delineate the disease variation among patients with this mutation and to define the c.-32-13T-->G haplotypes in search for genotype-phenotype correlations. METHODS: We studied 98 compound heterozygotes with a fully deleterious mutation (11 novel mutations are described) and the common c.-32-13T-->G mutation. RESULTS: All patients were Caucasian. None had the classic infantile form of Pompe disease. The clinical course varied far more than anticipated (age at diagnosis <1 to 78 years; age at onset: <1 to 52 years). The acid alpha-glucosidase activities in a subset of patients ranged from 4 to 19.9 nmol/mg/h. Twelve different c.-32-13T-->G haplotypes were identified based on 17 single-nucleotide polymorphisms located in the GAA gene. In 76% of the cases, c.-32-13T-->G was encountered in the second most common GAA core haplotype (DHRGEVVT). In only one case was c.-32-13T-->G encountered in the major GAA core haplotype (DRHGEIVT). CONCLUSION: Patients with the same c.-32-13T-->G haplotype (c.q. GAA genotype) may manifest first symptoms at different ages, indicating that secondary factors may substantially influence the clinical course of patients with this mutation.

[Tuberous sclerosis complex type 1 (TSC1): diagnostic significance of the cutaneous mini-lesions in a familial presentation]. / Complejo esclerosis tuberosa tipo 1 (CET1): importancia diagnóstica de las minilesiones cutáneas en los casos de presentación familiar.

We present a family with tuberous sclerosis complex type 1 (TSC1). The family is formed by six patients. Two sibs, female and male, both patients having minor signs of the disorder. The woman have two daughters, one of them with severe clinical and radiological features of TSC1, and the other who only has a small cutaneous acromic spot. The man has two sons, one with severe features of TSC1, and the other with cutaneous mini-lesions. DNA study of the two cousins, woman and man, with cutaneous mini-lesions, showed a mutation in the chromosome 9 (1749 del GA) (TSC1 ex 15) in both patients. No pathogenic mutation in the TSC2 gene was detected in the two cousins.

Large deletion at the TSC1 locus in a family with tuberous sclerosis complex.

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation and the development of hamartomas in a variety of organs and tissues. The disease is caused by mutations in either the TSC1 gene on chromosome 9q34, or the TSC2 gene on chromosome 16p13.3. Here we describe a deletion encompassing the TSC1 gene and two neighboring transcripts on chromosome 9q34 in six affected individuals from a family with TSC. To our knowledge, this is the first report of such a large deletion at the TSC1 locus and indicates that screening for similar mutations at the TSC1 locus is warranted in individuals with TSC.

Regulation of tuberous sclerosis complex (TSC) function by 14-3-3 proteins.

Tuberous sclerosis complex (TSC) is a genetic disorder characterized by seizures, mental disability, renal dysfunction and dermatological abnormalities. The disease is caused by inactivation of either hamartin or tuberin, the products of the TSC1 and TSC2 tumour-suppressor genes. Hamartin and tuberin form a complex and antagonise phosphoinositide 3-kinase/protein kinase B/target of rapamycin signal transduction by inhibiting p70 S6 kinase, an activator of translation, and activating 4E-binding protein 1, an inhibitor of translation initiation. Phosphorylation-dependent binding between tuberin and members of the 14-3-3 protein family indicates how the tuberin-hamartin complex may interact with upstream and downstream effectors, and suggests how phosphorylation-dependent regulation of the complex may be controlled.

[From gene to disease; progressive myoclonus epilepsy of Unverricht-Lundborg and mutations in the cystatin B gene]. / Van gen naar ziekte; progressieve myoclonusepilepsie van Unverricht-Lundborg en mutaties in het cystatine-B-gen.

Progressive myoclonus epilepsy type 1 of Unverricht-Lundborg (EPM1) is a rare disorder, associated with mutations in the cystatin B (CSTB) gene. The most prevalent molecular abnormality is an expansion of a dodecamer repeat in the promoter region of the CSTB gene, but point mutations in the CSTB gene have also been found. DNA examination may be useful in discriminating EPM1 from juvenile myoclonic epilepsy, and from other types of progressive myoclonus epilepsy. An early diagnosis is important to optimise treatment and to provide an adequate prognosis and prediction of recurrence.

Genetic risk factors in infertile men with severe oligozoospermia and azoospermia.

BACKGROUND: Male infertility due to severe oligozoospermia and azoospermia has been associated with a number of genetic risk factors. METHODS: In this study 150 men from couples requesting ICSI were investigated for genetic abnormalities, such as constitutive chromosome abnormalities, microdeletions of the Y chromosome (AZF region) and mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. RESULTS: Genetic analysis identified 16/150 (10.6%) abnormal karyotypes, 8/150 (5.3%) AZFc deletions and 14/150 (9.3%) CFTR gene mutations. An abnormal karyotype was found both in men with oligozoospermia and azoospermia: 9 men had a sex-chromosomal aneuploidy, 6 translocations were identified and one marker chromosome was found. Y chromosomal microdeletions were mainly associated with male infertility, due to testicular insufficiency. All deletions identified comprised the AZFc region, containing the Deleted in Azoospermia (DAZ) gene. CFTR gene mutations were commonly seen in men with congenital absence of the vas deferens, but also in 16% of men with azoospermia without any apparent abnormality of the vas deferens. CONCLUSIONS: A genetic abnormality was identified in 36/150 (24%) men with extreme oligozoospermia and azoospermia. Application of ICSI in these couples can result in offspring with an enhanced risk of unbalanced chromosome complement, male infertility due to the transmission of a Y-chromosomal microdeletion, and cystic fibrosis if both partners are CFTR gene mutation carriers. Genetic testing and counselling is clearly indicated for these couples before ICSI is considered.