Martin Kehrer

Development of Cerebral Blood Flow Volume in Preterm Neonates during the First Two Weeks of Life

To investigate the postnatal development of cerebral perfusion in preterm neonates with normal brains over the first 2 wk of life, a prospective longitudinal study was designed. Quantitative measurement of cerebral blood flow (CBF) volume was performed using ultrasound flowmetry of the extracranial, brain-feeding arteries in 32 preterm infants of 28–35 wk gestational age. Measurements were done in the internal carotid and vertebral arteries of both sides on d 1, 2, 3, 7, and 14 after birth. A 10.0-MHz linear transducer of a computed sonography system (Acuson 128/XP10) was used. Intravascular flow volumes were calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. Mean CBF volume increased markedly over the first 2 wk. One-third of this rise already occurred from the first to the second postnatal day, thereafter there was a continuous increase from d 2 to d 14 of life. Whereas the absolute level of CBF volume was primarily determined by postmenstrual age, the pattern of postnatal changes in CBF volume was found to be independent of gestational age. Arterial carbon dioxide tension, mean arterial blood pressure, and hematocrit had no influence on the development of CBF volume. The pronounced increase of CBF volume from d 1 to d 2 is likely to represent a normal adaptive response of the cerebral circulation to postnatal life. The data presented here may serve as the basis for further studies to investigate whether deviations from this adaptive response are associated with an increased risk of brain injury.

Next-generation sequencing in X-linked intellectual disability

X-linked intellectual disability (XLID) is a genetically heterogeneous disorder with more than 100 genes known to date. Most genes are responsible for a small proportion of patients only, which has hitherto hampered the systematic screening of large patient cohorts. We performed targeted enrichment and next-generation sequencing of 107 XLID genes in a cohort of 150 male patients. Hundred patients had sporadic intellectual disability, and 50 patients had a family history suggestive of XLID. We also analysed a sporadic female patient with severe ID and epilepsy because she had strongly skewed X-inactivation. Target enrichment and high parallel sequencing allowed a diagnostic coverage of >10 reads for ~96% of all coding bases of the XLID genes at a mean coverage of 124 reads. We found 18 pathogenic variants in 13 XLID genes (AP1S2, ATRX, CUL4B, DLG3, IQSEC2, KDM5C, MED12, OPHN1, SLC9A6, SMC1A, UBE2A, UPF3B and ZDHHC9) among the 150 male patients. Thirteen pathogenic variants were present in the group of 50 familial patients (26%), and 5 pathogenic variants among the 100 sporadic patients (5%). Systematic gene dosage analysis for low coverage exons detected one pathogenic hemizygous deletion. An IQSEC2 nonsense variant was detected in the female ID patient, providing further evidence for a role of this gene in encephalopathy in females. Skewed X-inactivation was more frequently observed in mothers with pathogenic variants compared with those without known X-linked defects. The mutation rate in the cohort of sporadic patients corroborates previous estimates of 5–10% for X-chromosomal defects in male ID patients.

Varying clinical presentations at onset of type 1 diabetes mellitus in children – epidemiological evidence for different subtypes of the disease?

Abstract: Objective:  On the basis of 2121 case observations between 1987 and 1997, we describe the clinical and laboratory characteristics of diabetes mellitus type 1 at its onset. Our objective is to analyze whether clinical presentation follows a uniform pattern or whether there is evidence for different subtypes.

A Longitudinal Study of Cerebral Blood Flow Over the First 30 Months

To investigate prospectively the development of cerebral perfusion during infancy, serial quantitative measurements of cerebral blood flow (CBF) volume were performed in two healthy children from birth up to the age of 30 mo. A total of 28 CBF volume measurements were done in either of the children. Absolute flows were measured in the internal carotid and vertebral arteries on both sides. Blood flow was calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. Starting from 67 and 80 mL/min, respectively, at birth an almost 10-fold increase of CBF volume was observed in both children during the examination period. Half of this rise occurred during the first 6 mo, probably reflecting the steep metabolic incline during this period of synaptogenesis. The continuous increase in CBF volume after the sixth month of life mainly corresponds to brain growth. Estimated CBF (based on estimated brain weights) increased from 21 and 23 mL 100 g−1 min−1, respectively, after birth to 46 and 53 mL 100 g−1 min−1, respectively, during the first 6 mo of life in both children, remaining stable thereafter. This study is the first to provide longitudinal data of CBF during the first 30 mo after birth.

Interstitial duplication of chromosome region 1q25.1q25.3: Report of a patient with mild cognitive deficits, tall stature and facial dysmorphisms

Isolated interstitial duplications of chromosome band 1q25 are apparently very rare; no patients with detailed molecular and clinical characterization of duplications restricted to this region have been published to date. We report on a 9‐year‐old girl with mild cognitive deficits, tall stature, macrocephaly and discrete dysmorphic features in whom a de novo interstitial 7.5 Mb duplication of 1q25.1q25.3 was detected by SNP array analysis (arr[hg19] 1q25.1q25.3(173,925,505–181,381,242)x3 dn). The duplicated region was inversely inserted into chromosome band 1q42.2: 46,XX,der(1)(pter→q42.2::q25.3→q25.1::q42.2→qter). Overexpression of one or several of the 87 genes in the duplicated interval was presumably the major causative factor for the clinical manifestations. Reports of additional patients with overlapping duplications will be needed to establish detailed karyotype‐phenotype correlations and to gain a better understanding of the underlying pathomechanisms.

Interstitial 1p32.1p32.3 deletion in a patient with multiple congenital anomalies.

Interstitial deletions encompassing chromosome bands 1p32.1p32.3 are rare. Only nine unrelated patients with partially overlapping 1p32.1p32.3 deletions of variable size and position have been reported to date. We report on a 17‐month‐old boy with choanal atresia, hearing loss, urogenital anomalies, and microcephaly in whom an interstitial de novo deletion of 6.4 Mb was detected in 1p32.1p32.3 (genomic position chr1:54,668,618‐61,113,264 according to GRCh37/hg19). The deleted region harbors 31 RefSeq genes. Notable genes in the region are PCSK9, haploinsufficiency of which caused low LDL cholesterol plasma levels in the patient, and DAB1, which is a candidate gene for cognitive deficits, microcephaly, and cerebral abnormalities such as ventriculomegaly and agenesis of the corpus callosum. Choanal atresia, microcephaly, and severe hearing loss were previously not known to be associated with 1p32 deletions. Our reported patient thus broadens the spectrum of clinical findings in this chromosome region and further facilitates genotype‐phenotype correlations. Additional patients with overlapping deletions and/or point mutations in genes of this region need to be identified to elucidate the role of individual genes for the complex clinical manifestations.

12q24.33 deletion: Report of a patient with intellectual disability and review of the literature

Deletions of chromosome band 12q24.33 are rare. We report on a 17‐year‐old male patient with intellectual disability but no major malformations or dysmorphic features in whom a de novo interstitial 660 kb deletion in 12q24.33 was detected by SNP array analysis. This deletion was secondary to a translocation t(12;14)(q24.3;q13)dn that also led to a small deletion in 14q21.1 and a small duplication in 2p23.1. The deletion overlaps with two previously published larger deletions in patients who suffered from intellectual disability, obesity, and polycystic kidney disease, indicating that haploinsufficiency of one or several of the genes in the deleted interval of the patient reported here causes intellectual deficits, but not obesity or renal problems. The 14 RefSeq genes that are harbored by this deletion include P2RX2, which had previously been proposed as a candidate gene for intellectual disability. Thus, the patient reported here broadens our knowledge of the phenotypic consequences of deletions in 12q24.33 and facilitates genotype–phenotype correlations for chromosome aberrations of this region.