Novel germline variants of CDKN1B and CDKN2C identified during screening for familial primary hyperparathyroidism

PURPOSE

CDKN1B mutations were established as a cause of multiple endocrine neoplasia 4 (MEN4) syndrome in patients with MEN1 phenotype without a mutation in the MEN1 gene. In addition, variants in other cyclin-dependent kinase inhibitors (CDKIs) were found in some MEN1-like cases without the MEN1 mutation. We aimed to describe novel germline mutations of these genes in patients with primary hyperparathyroidism (PHPT).

METHODS

During genetic screening for familial hyperparathyroidism, three novel CDKIs germline mutations in three unrelated cases between January 2019 and November 2021 were identified. In this report, we describe clinical features, DNA sequence analysis, and familial segregation studies based on these patients and their relatives. Genome-wide DNA study of loss of heterozygosity (LOH), copy number variation (CNV), and p27/kip immunohistochemistry was performed on tumour samples.

RESULTS

DNA screening was performed for atypical parathyroid adenomas in cases 1 and 2 and for cystic parathyroid adenoma and young age at diagnosis of PHPT in case 3. Genetic analysis identified likely pathogenic variants of CDKN1B in cases 1 and 2 and a variant of the uncertain significance of CDKN2C, with uniparental disomy in the tumour sample, in case 3. Neoplasm screening of probands showed other non-endocrine tumours in case 1 (colon adenoma with dysplasia and atypical lipomas) and case 2 (aberrant T-cell population) and a non-functional pituitary adenoma in case 3.

CONCLUSION

Germline mutations in CDKIs should be included in gene panels for genetic testing of primary hyperparathyroidism. New germline variants here described can be added to the current knowledge.

Characterization of six marker chromosomes by comparative genomic hybridization

We applied comparative genomic hybridization (CGH) in six patients with de novo prenatal or postnatal extra marker chromosomes (MC). In four cases, MCs were mosaic and in one of them, the MC was detected in less than 50% of the cells. In three cases, CGH identified the origin of the extra MCs. In the other three, two prenatal cases and one child with an abnormal phenotype, CGH showed normal profiles. Among these cases, a normal profile and entirely C-band positive was identified suggesting that MC did not contain euchromatin. Genetic imbalances detected by CGH were as follow: a gain of 8p10-p12 in a boy with facial dysmorphism, hyperactivity and speech delay, a gain of 8q10-q12 in a healthy man with a history of spontaneous abortions, and a gain of 15q11-q13 in a girl with speech delay, and motor skill and object manipulation difficulties. Clinical data of these patients were compared with those reported in the literature. We conclude that CGH is a very useful and powerful tool for characterizing prenatal or postnatal MCs, even when the mosaicism is present and the MCs are present in less than 50% of the cells.

Contribution of ultrasonographic examination to the prenatal detection of trisomy 21: experience from 19 European registers

The objective of this study was to evaluate the contribution of ultrasound scanning to the prenatal detection of trisomy 21 in a large unselected European population. Data from 19 congenital malformation registers in 11 European countries were included. The prenatal ultrasound screening programs in the countries ranged from no routine screening to three ultrasound investigations per patient. Routine serum screening was offered in four of the 11 countries and routine screening on the basis of maternal age amniocentesis in all. The results show that overall 53% of cases of trisomy 21 were detected prenatally with a range from 3% in Lithuania to 88% in Paris. Ninety-eight percent of women whose babies were diagnosed before 24 weeks gestation chose to terminate the pregnancy. Centres/countries that offer serum screening do not have a significantly higher detection rate of trisomy 21 when compared to those that offer maternal age amniocentesis and anomaly scanning only. Fifty percent of trisomy 21 cases were born to women aged 35 years or more. In conclusions, second trimester ultrasound plays an important role in the prenatal diagnosis of trisomy 21. Of those cases prenatally diagnosed, 64% of cases in women <35 years and 36% of those in women >or=35 years were detected because of an ultrasound finding. Ultrasound soft markers accounted for 84% of the scan diagnoses. There is evidence of increasing maternal age across Europe with 50% of cases of trisomy 21 born to women aged 35 years or more.

Prenatal detection of rare chromosomal autosomal abnormalities in Europe

The aim of the present study was to evaluate the prenatal detection of rare chromosomal autosomal abnormalities by ultrasound (US) examination. Data were obtained from 19 congenital malformation registries from 11 European countries, between 01/07/96 and 31/12/98. A total of 664,340 births were covered and 7,758 cases with congenital malformations were recorded. Rare autosomal abnormalities were diagnosed in 114 cases (6.6%) from a total of 1,738 chromosome abnormalities. There were a wide variety of autosomal abnormalities: the most common were deletions (33 cases), duplications (32 cases), trisomies of chromosomes 8, 9, 10, 14, 15, and 16 (23 cases), and unbalanced rearrangements (19 cases). Out of these cases, 45.6% were detected prenatally by US examination due to the presence of congenital anomaly. As for the types of chromosomal anomaly, unbalanced rearrangements and deletions were the most frequently detected by US. A high percentage of cases with balanced rearrangements were associated with severe congenital anomalies. The most frequent congenital anomalies detected by US were cystic hygroma (20.6%), central nervous system defects (17.6%), cardiac defects (13.2%), and diaphragm defects (10.3%). This large series offers useful information about prenatal diagnosis by US of congenital defects associated with rare autosomal abnormalities and it provides a valuable knowledge about outcome. Fetal anomalies detected by US that were associated with rare autosomal abnormalities were significantly more frequent than those associated with common chromosomal abnormalities (45.6 vs. 34.7%). This study indicates the need to increase the detection of congenital anomalies by US.

Contribution of ultrasonographic examination to the prenatal detection of chromosomal abnormalities in 19 centres across Europe

The objective of this study was to evaluate the prenatal detection of chromosomal abnormalities by fetal ultrasonographic examination in a large database provided by 19 Registries of Congenital Anomalies from 11 European countries. This study included 1738 cases of chromosomal abnormalities, liveborn, stillborn or termination of pregnancy regardless of maternal age from a population of 664,340 births during the period 1996 - 1998. The most frequent chromosomal anomalies were Down syndrome (n=1050), trisomy 18 (n=191), Turner syndrome (n=125), trisomy 13 (n=86), and triploidy (n=56). Fetal ultrasonographic examination resulted in the prenatal detection of 37.7% of the chromosomal abnormalities, thereby resulting in a reduction of 28.6% in their prevalence at birth due to terminations of pregnancy. The detection rate by ultrasound examination varied according to local policies of prenatal diagnosis : it was lower in countries where routine scan were not performed and higher in countries in which at least one routine anomaly scan during the second trimester of pregnancy was performed. The ultrasound detection varied according to the specific chromosomal anomaly and was lowest for Klinefelter syndrome (5.7%) and highest for triploidy (78.6%). For Down syndrome it was 26.4%. Termination of pregnancy was performed in 75.9% of the cases. Among the 655 cases detected by ultrasound, the most frequent ultrasound signs by category of chromosomal abnormalities were analysed. This study shows that ultrasound screening is an important tool in the prenatal detection of chromosomal abnormalities in Europe, leading to a significant reduction in the prevalence of livebirth children with chromosomal anomalies.

Fetal and placenta chromosome constitution in 237 pregnancy losses

The aim of the study was to carry out cytogenetic analyses in pregnancy losses. Samples of cartilage and placenta tissue were obtained prospectively from 237 pregnancy losses of more than 16 weeks of gestation (130 stillbirths, 97 induced abortions and 10 early neonatal deaths). Cartilage culture was performed in 222 samples and placental culture was initiated in 224. The overall culture success rate was 83.5%, 72.3% in stillbirths, 97% in induced abortions and 100% in early neonatal death. An abnormal karyotype was detected in 52 cases: 6.9% in stillbirths, 43.6% in induced abortions and 20% in early neonatal deaths. The rate of discrepancy between the prenatal cytogenetic results in amniotic fluid and the post-termination karyotype was 3%. The tissue of choice for cytogenetic analysis was cartilage in induced abortions and early neonatal death, and placenta in stillbirth. The majority of cases had a chromosome abnormality: multiple congenital anomalies in 74.6%, and a single major anomaly in 9.7%.

Origin of trisomy 21 in Down syndrome cases from a Spanish population registry

We have carried out a population-based study on the origin of the extra chromosome 21 in 38 families with Down syndrome (DS) offspring in El Vallès (Spain). From 1991 to 1994, a higher prevalence of DS (22.7/10000 live births, stillbirths and induced abortions) was found compared to the majority of EUROCAT registries. The distribution of trisomy 21 by origin was 88% maternal (90.6% meiosis I, 6.2% meiosis II, 3.1% maternal mosaicism), 5.6% paternal (50% meiosis I, 50% meiosis II) and 5.6% mitotic. The percentage of parental mosaicism was 2.7%. These percentages are similar to those previously reported. Recombination study revealed a maternal meiosis I genetic map of 32.68 cM (approximately one-half the length of the normal female map). Mean maternal age among non-recombinant cases involving MI errors was significantly lower (31.1 years) than among those cases showing one observable crossover (36.1 years) (P<0.05); this could support the hypothesis that 'achiasmate' chromosomes may be subject to aberrant segregation regardless of maternal age.

Chromosome 21 disomy in the spermatozoa of the fathers of children with trisomy 21, in a population with a high prevalence of Down syndrome: increased incidence in cases of paternal origin

Between April 1991 and December 1994, epidemiological studies detected a population with a high prevalence of Down syndrome in El Vallès, Spain. Parallel double studies were carried out to determine the parental and the meiotic origins of the trisomy 21, by use of DNA polymorphisms, and to establish the incidence of disomy 21 in the spermatozoa of the fathers of affected children, by use of multicolor FISH. Results show that the overall incidence of chromosome 21 disomy in the fathers of affected children was not significantly different from that in the control population (0.31% vs. 0.37%). However, analysis of individual data demonstrates that two cases (DP-4 and DP-5) with significant increases of disomy 21 (0. 75% and 0.78% vs. 0.37%) correspond to the fathers of the two individuals with Down syndrome of paternal origin. DP-5 also had a significant increase of sex-chromosome disomies (0.69% vs. 0.37%) and of diploid spermatozoa (1.13% vs. 0.24%).