First prenatal diagnosis of a 'pure' 9q34.3 deletion (Kleefstra syndrome): A case report and literature review.

Kleefstra syndrome (KS) is characterized by developmental delay, intellectual disability, hypotonia and distinct facial features. Additional clinical features include congenital heart defects, cerebral abnormalities, urogenital defects and weight gain. The syndrome is caused by a microdeletion in chromosomal region 9q34.3 (in 85% of cases) or by a mutation in the EHMT1 gene coding for euchromatin histone methyltransferase 1. The prenatal phenotype has not yet been characterized. Herein, we sought to define this phenotype on the basis of a new case report and literature review.

A molecular-based estimation of the prevalence of hypophosphatasia in the European population.

The prevalence of hypophosphatasia (HP), a rare metabolic disorder due to loss-of-function mutations in the ALPL gene, has never been estimated in the European population. Only one published study evaluated the incidence of severe HP at 1/100,000 in Canada 53 years ago. Moderate forms of hypophosphatasia (mHP), including HP with moderate bone features and the mildest form odontohypophosphatasia, reflect both recessive and dominant inheritance, and are therefore expected to be more frequent than severe forms of HP. Here we estimated both the prevalences of severe and mHP in European populations. The prevalence of severe HP was estimated at 1/300,000 on the basis of the number of cases tested in our laboratory and originating from France during the period 2000-2009. The prevalence of mHP was then estimated by using the proportion of dominant mutations among severe alleles and by estimating the penetrance of the disease in heterozygotes for dominant mutations. According to a genetic model with four alleles resulting in 10 distinct genotypes, the prevalence of dominant mHP in the European population was estimated to be 1/6370, pointing out that mHP is much more frequent than severe HP.

Mild forms of hypophosphatasia mostly result from dominant negative effect of severe alleles or from compound heterozygosity for severe and moderate alleles.

BACKGROUND: Mild hypophosphatasia (HPP) phenotype may result from ALPL gene mutations exhibiting residual alkaline phosphatase activity or from severe heterozygous mutations exhibiting a dominant negative effect. In order to determine the cause of our failure to detect a second mutation by sequencing in patients with mild HPP and carrying on a single heterozygous mutation, we tested the possible dominant effect of 35 mutations carried by these patients. METHODS: We tested the mutations by site-directed mutagenesis. We also genotyped 8 exonic and intronic ALPL gene polymorphisms in the patients and in a control group in order to detect the possible existence of a recurrent intronic mild mutation. RESULTS: We found that most of the tested mutations exhibit a dominant negative effect that may account for the mild HPP phenotype, and that for at least some of the patients, a second mutation in linkage disequilibrium with a particular haplotype could not be ruled out. CONCLUSION: Mild HPP results in part from compound heterozygosity for severe and moderate mutations, but also in a large part from heterozygous mutations with a dominant negative effect.

Characterization of missense mutations and large deletions in the ALPL gene by sequencing and quantitative multiplex PCR of short fragments.

Hypophosphatasia is a rare inherited bone disorder characterized by defective bone and dental mineralization and deficiency of serum and liver/bone/kidney alkaline phosphatase activity. The disease is due to mutations in the alkaline phosphatase liver-type (ALPL) gene. Gross deletions or insertions have not previously been reported in this gene. We report here the characterization of nine novel ALPL gene mutations in a series of 8 patients affected by various forms of hypophosphatasia. The newly discovered mutations included five missense mutations (c.368C --> A, c.814C--> T, c.1196C--> T, c.1199C--> T, c.1283G--> C), two small deletions (c.797_802del, c.1044_1055del), and two large deletions. The large deletions were detected by quantitative multiplex polymerase chain reaction (PCR) of short fluorescent fragments (QMPSF). We conclude that QMPSF slightly reduces the proportion of undetected mutations in hypophosphatasia and improves genetic counselling in the affected families.

15q11.2 microdeletion (BP1-BP2) and developmental delay, behaviour issues, epilepsy and congenital heart disease: a series of 52 patients.

Proximal region of chromosome 15 long arm is rich in duplicons that, define five breakpoints (BP) for 15q rearrangements. 15q11.2 microdeletion between BP1 and BP2 has been previously associated with developmental delay and atypical psychological patterns. This region contains four highly-conserved and non-imprinted genes: NIPA1, NIPA2, CYFIP1, TUBGCP5. Our goal was to investigate the phenotypes associated with this microdeletion in a cohort of 52 patients. This copy number variation (CNV) was prevalent in 0.8% patients presenting with developmental delay, psychological pattern issues and/or multiple congenital malformations. This was studied by array-CGH at six different French Genetic laboratories. We collected data from 52 unrelated patients (including 3 foetuses) after excluding patients with an associated genetic alteration (known CNV, aneuploidy or known monogenic disease). Out of 52 patients, mild or moderate developmental delay was observed in 68.3%, 85.4% had speech impairment and 63.4% had psychological issues such as Attention Deficit and Hyperactivity Disorder, Autistic Spectrum Disorder or Obsessive-Compulsive Disorder. Seizures were noted in 18.7% patients and associated congenital heart disease in 17.3%. Parents were analysed for abnormalities in the region in 65.4% families. Amongst these families, 'de novo' microdeletions were observed in 18.8% and 81.2% were inherited from one of the parents. Incomplete penetrance and variable expressivity were observed amongst the patients. Our results support the hypothesis that 15q11.2 (BP1-BP2) microdeletion is associated with developmental delay, abnormal behaviour, generalized epilepsy and congenital heart disease. The later feature has been rarely described. Incomplete penetrance and variability of expression demands further assessment and studies.

Hypophosphatasia: molecular testing of 19 prenatal cases and discussion about genetic counseling.

OBJECTIVE: We studied hypophosphatasia (HP) mutations in 19 cases prenatally detected by ultrasonography without familial history of HP. We correlated the mutations with the reported ultrasound signs, and discussed genetic counseling with regard to the particular dominantly inherited prenatal benign form of HP. METHOD: The coding sequence of the tissue nonspecific alkaline phosphatase (TNSALP) gene was analyzed by DNA sequencing, and 3D modeling was used to locate the mutated amino acids with regard to the functional domains of TNSALP. RESULTS: Although reported ultrasound signs were heterogeneous, two mutated alleles were found in 18 of the 19 cases studied, indicating recessive transmission of the disease. Functional domains of TNSALP were affected by 74% of missense mutations. In all the cases, including one with only a heterozygous mutation, molecular, biological, and familial data do not corroborate the hypothesis of prenatal benign HP. The mutation c.1133A>T observed in the prenatal benign form of HP and common in USA was not found in this series. CONCLUSION: The results point out the prenatally detectable allelic heterogeneity of HP. The nature of the detected mutations and the evidence of recessive inheritance do not support these cases being affected with prenatal benign HP.