Partial monosomy 21 was recently segregated into three regions associated with variable clinical severity. We describe 10 new patients, all examined by single nucleotide polymorphism (SNP) genotyping and G-banded karyotyping. Cohort A consisted of three patients seen in our medical genetics clinics with partial chromosome 21 monosomies. In two of these patients having terminal deletions (21q22.2-ter and 21q22.3-ter), the breakpoints differed by at least 812 Kb of sequence, containing seven RefSeq genes. A third patient had an interstitial hemizygous loss of 16.4 Mb (21q21.1-q22.11). All three patients had relatively mild phenotypes. Cohort B consisted of seven patients with partial chromosome 21 monosomies who had a greater number of dysmorphic features and some major malformations; SNP genotypes were obtained from the Coriell Genetic Cell Repository. We also collected data on partial monsomy 21 cases from the DECIPHER database. This report of 10 new cases of 21q deletion and review of a total of 36 confirms that deletion of the terminal region is associated with a mild phenotype, but suggests that deletion of regions 1 and 2 is compatible with life and have a variable phenotype perhaps relating more to other genetic and environmental variables than to genes in the interval.
Microdeletion and microduplication genetic syndromes are known to be a significant cause of developmental delay and dysmorphology. Utilizing high-resolution chromosome analysis, array CGH and SNP technologies we identified a novel genomic syndrome comprising of an interstitial duplication of approximately 1.61 Mb at the distal end of chromosome 3 band q29. The imbalance was present in five individuals in a three generation family with clinical features including mild to moderate mental retardation and microcephaly. The duplicated segment overlaps with and is the genomic counterpart of the recently described microdeletion of 3q29. Both syndromes are proposed to occur by non-allelic homologous recombination between regions of low copy repeats present around the breakpoints.
We report on the analyses of four unrelated patients with de novo, overlapping, hemizygous deletions of the long arm of chromosome 10. These include two small terminal deletions (10q26.2 to 10qter), a larger terminal deletion (10q26.12 to 10qter), and an interstitial deletion (10q25.3q26.13). Single nucleotide polymorphism (SNP) studies (Illumina 550 K) established that these deletions resulted in the hemizygous loss of ∼6.1, ∼6.1, ∼12.5, and ∼7.0 Mb respectively. Additionally, these data establish that Patients 1, 2, and 3 share common, distal, hemizygous deleted regions of 6.09 Mb containing 37 RefSeq genes. Patients 3 and 4 share a 2.52 Mb deleted region corresponding to the proximal deleted region of Patient 3 and the distal deleted region of Patient 4. This common, hemizygous region contains 20 RefSeq genes including two H6 family homeobox genes (HMX2 and HMX3). Based on previous reports that Hmx2/Hmx3 knockout mice have vestibular anomalies, we propose that hemizygous deletions of HMX2 and HMX3 are responsible for the inner ear malformations observed from CT images, vestibular dysfunction, and congenital sensorineural hearing loss found in Patients 3 and 4.
CPT Carnitine palmitoyltransferase MDC1ACongenital muscular dystrophy type 1A SLO Smith-Lemli-Opitz syndrome SMA Spinal muscular atrophy AIM Hypotonia is a symptom of diminished tone of skeletal muscle associated with decreased resistance of muscles to passive stretching, which can be caused by abnormalities of the central nervous system, any element of the lower motoneuron, or both. Hypotonia is not a specific diagnosis, but can be part of over 500 different genetic disorders, with many other conditions waiting to be identified. This review proposes a pragmatic approach to evaluating hypotonia in neonatal and pediatric populations by using a diagnostic algorithm.METHOD We use a dedicated literature review combined with clinical experience in a newly established multidisciplinary center for hypotonia to establish a diagnostic algorithm.RESULTS Hypotonia can be a symptom of over 500 different genetic disorders. It can present as peripheral, central, or combined hypotonia, providing necessity for rational and systematic diagnostic testing.INTERPRETATION Our analyses demonstrate that a staged diagnostic approach categorizing patients as having peripheral, central, or combined hypotonia is the most efficient to providing a rational work-up. Establishing a diagnosis is crucial for prognosis, management, and treatment strategies, and for ascertaining an accurate recurrence risk for future offspring in a family.
Pompe disease (PD) is an autosomal recessive lysosomal storage disorder causing progressive glycogen accumulation in muscles, with variability in age of onset and severity. For infantile-onset PD (IOPD), initiation of early treatment can be life-saving; however, current newborn screening (NBS) technology cannot distinguish IOPD from late-onset PD (LOPD) without clinical workup. Therefore, families of LOPD infants diagnosed by NBS may now spend years or even decades aware of their illness before symptoms appear, creating a pre-symptomatic awareness phase with which the medical community has little experience. The present study examines the effects of receiving a positive NBS result for PD on families. In-depth qualitative interviews were conducted with mothers of nine children (three IOPD and six LOPD) diagnosed via NBS, exploring their experiences, understanding of PD, how they are coping, and what impact diagnosis is having on family life. Interviews were coded using MaxQDA v.12 and analyzed for thematic trends. While overall opinion of NBS was favorable, it is clear many of the concerns anticipated by HCPs, patients, and families regarding NBS for late-onset LSDs are being realized to varying degrees; LOPD families are becoming patients-in-waiting. Increased fear/anxiety and living with uncertainty (regarding diagnosis, their children's future, and when to start treatment) were predominant themes, with all families voicing considerable emotional reactions and varied social and healthcare support concerns. Coping strategies and psychosocial challenges are interpreted using Rolland & Williams' Family Systems Genetic Illness model. Recommendations for improvement in delivery of service, as well as families' advice for future parents and HCPs, are discussed.
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