PHKA2 variants expand the phenotype of phosphorylase B kinase deficiency to include patients with ketotic hypoglycemia only.

Idiopathic ketotic hypoglycemia (IKH) is a diagnosis of exclusion with glycogen storage diseases (GSDs) as a differential diagnosis. GSD IXa presents with ketotic hypoglycemia (KH), hepatomegaly, and growth retardation due to PHKA2 variants. In our multicenter study, 12 children from eight families were diagnosed or suspected of IKH. Whole-exome sequencing or targeted next-generation sequencing panels were performed. We identified two known and three novel (likely) pathogenic PHKA2 variants, such as p.(Pro869Arg), p.(Pro498Leu), p.(Arg2Gly), p.(Arg860Trp), and p.(Val135Leu), respectively. Erythrocyte phosphorylase kinase activity in three patients with the novel variants p.(Arg2Gly) and p.(Arg860Trp) were 15%-20% of mean normal. One patient had short stature and intermittent mildly elevated aspartate aminotransferase, but no hepatomegaly. Family testing identified two asymptomatic children and 18 adult family members with one of the PHKA2 variants, of which 10 had KH symptoms in childhood and 8 had mild symptoms in adulthood. Our study expands the classical GSD IXa phenotype of PHKA2 missense variants to a continuum from seemingly asymptomatic carriers, over KH-only with phosphorylase B kinase deficiency, to more or less complete classical GSD IXa. In contrast to typical IKH, which is confined to young children, KH may persist into adulthood in the KH-only phenotype of PHKA2.

Absence of an osteopetrosis phenotype in IKBKG (NEMO) mutation-positive women: A case-control study.

BACKGROUND: NF-κB essential modulator (NEMO), encoded by IKBKG, is necessary for activation of the ubiquitous transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Animal studies suggest NEMO is required for NF-κB mediated bone homeostasis, but this has not been thoroughly studied in humans. IKBKG loss-of-function mutation causes incontinentia pigmenti (IP), a rare X-linked disease featuring linear hypopigmentation, alopecia, hypodontia, and immunodeficiency. Single case reports describe osteopetrosis (OPT) in boys carrying hypomorphic IKBKG mutations. METHOD: We studied the bone phenotype in women with IP with evaluation of radiographs of the spine and non-dominant arm and leg; lumbar spine and femoral neck aBMD using DXA; µ-CT and histomorphometry of trans-iliac crest biopsy specimens; bone turnover markers; and cellular phenotype in bone marrow skeletal (stromal) stem cells (BM-MSCs) in a cross-sectional, age-, sex-, and BMI-matched case-control study. X-chromosome inactivation was measured in blood leucocytes and BM-MSCs using a PCR method with methylation of HpaII sites. NF-κB activity was quantitated in BM-MSCs using a luciferase NF-κB reporter assay. RESULTS: Seven Caucasian women with IP (age: 24-67 years and BMI: 20.0-35.2 kg/m2) and IKBKG mutation (del exon 4-10 (n = 4); c.460C>T (n = 3)) were compared to matched controls. The IKBKG mutation carriers had extremely skewed X-inactivation (>90:10%) in blood, but not in BM-MSCs. NF-κB activity was lower in BM-MSCs from IKBKG mutation carriers (n = 5) compared to controls (3094 ±â€¯679 vs. 5422 ±â€¯1038/µg protein, p < 0.01). However, no differences were identified on skeletal radiographics, aBMD, µ-architecture of the iliac crest, or bone turnover markers. The IKBKG mutation carriers had a 1.7-fold greater extent of eroded surfaces relative to osteoid surfaces (p < 0.01), and a 2.0-fold greater proportion of arrested reversal surface relative to active reversal surface (p < 0.01). CONCLUSION: Unlike mutation-positive males, the IKBKG mutation-positive women did not manifest OPT.

Boucher Neuhäuser Syndrome - A rare cause of inherited hypogonadotropic hypogonadism. A case of two adult siblings with two novel mutations in PNPLA6.

Boucher Neuhäuser Syndrome (BNS) is a rare clinical syndrome with autosomal recessive inheritance defined by early-onset ataxia, hypogonadism and chorioretinal dystrophy. We present two siblings diagnosed with BNS in late adult life identified with compound heterozygous state of two novel PNPLA6 mutations. Five healthy siblings were non- or heterozygous carriers of the mutations. The cases, which presented with ataxia in childhood and hypogonadotropic hypogonadism (HH), were diagnosed at age 17 and 25, respectively, when examined for delayed puberty. The youngest case, a 55-year old male, was referred to our department in 2006 for evaluation of secondary causes of osteoporosis, which he developed despite adequate testosterone replacement therapy. The unusual medical history with childhood ataxia and hypogonadotropic hypogonadism lead to further examinations and eventually the diagnosis of BNS. The older sister of the proband also displayed the triad of ataxia, HH and chorioretinal dystrophy accompanied by cerebellar atrophy and in 2014, we found the mutations in PNPLA6. BNS is a rare cause of HH and secondary osteoporosis, but should be considered in patients presenting with one or more of the key features. Genetic screening is becoming increasingly available and inexpensive and accordingly this may be considered earlier and by broader indication in unusual phenotypic presentations. The increasing knowledge of causes for inherited diseases should extend the use of genetic screening, as the correct diagnosis will benefit the patients.

Neonatal High Bone Mass With First Mutation of the NF-κB Complex: Heterozygous De Novo Missense (p.Asp512Ser) RELA (Rela/p65).

Heritable disorders that feature high bone mass (HBM) are rare. The etiology is typically a mutation(s) within a gene that regulates the differentiation and function of osteoblasts (OBs) or osteoclasts (OCs). Nevertheless, the molecular basis is unknown for approximately one-fifth of such entities. NF-κB signaling is a key regulator of bone remodeling and acts by enhancing OC survival while impairing OB maturation and function. The NF-κB transcription complex comprises five subunits. In mice, deletion of the p50 and p52 subunits together causes osteopetrosis (OPT). In humans, however, mutations within the genes that encode the NF-κB complex, including the Rela/p65 subunit, have not been reported. We describe a neonate who died suddenly and unexpectedly and was found at postmortem to have HBM documented radiographically and by skeletal histopathology. Serum was not available for study. Radiographic changes resembled malignant OPT, but histopathological investigation showed morphologically normal OCs and evidence of intact bone resorption excluding OPT. Furthermore, mutation analysis was negative for eight genes associated with OPT or HBM. Instead, accelerated bone formation appeared to account for the HBM. Subsequently, trio-based whole exome sequencing revealed a heterozygous de novo missense mutation (c.1534_1535delinsAG, p.Asp512Ser) in exon 11 of RELA encoding Rela/p65. The mutation was then verified using bidirectional Sanger sequencing. Lipopolysaccharide stimulation of patient fibroblasts elicited impaired NF-κB responses compared with healthy control fibroblasts. Five unrelated patients with unexplained HBM did not show a RELA defect. Ours is apparently the first report of a mutation within the NF-κB complex in humans. The missense change is associated with neonatal osteosclerosis from in utero increased OB function rather than failed OC action. These findings demonstrate the importance of the Rela/p65 subunit within the NF-κB pathway for human skeletal homeostasis and represent a new genetic cause of HBM.

Case report: vitamin D-dependent rickets type 1 caused by a novel CYP27B1 mutation.

Vitamin D-dependent rickets type 1 VDDR-1 is a recessive inherited disorder with impaired activation of vitamin D, caused by mutations in CYP27B1. We present long-time follow-up of a case with a novel mutation including high-resolution peripheral quantitative computed tomography of the bone. Adequate treatment resulted in a normalized phenotype.

Blue cone monochromatism in a female due to skewed X-inactivation.

Blue cone monochromatism (BCM) is a rare cone dystrophy with recessive X-linked inheritance and therefore diagnosed in males whereas females are clinically unaffected. We present a female with clinically manifested BCM. The diagnosis was genetically verified with the identification of one single red-green OPN1LW/MW hybrid gene harboring a point mutation c.607C>G, p.Cys203Arg that associates with BCM and in addition a completely biased X-inactivation in DNA isolated from full blood and buccal mucosa. The present case illustrates that females may develop symptoms of recessive X-linked eye diseases in rare cases.

A novel mitochondrial mutation m.8989G>C associated with neuropathy, ataxia, retinitis pigmentosa - the NARP syndrome.

The archetypal NARP syndrome is almost exclusively associated with the m.8993T>C/G mutation in the sixth subunit of the mitochondrial ATP synthase, whereas other mutations in the MT-ATP6 gene primarily associate with Leigh syndrome or Leber's hereditary optic neuropathy (LHON). We report a novel mitochondrial point mutation, m.8989G>C, in a patient presenting with neuropathy, ataxia and retinitis pigmentosa constituting the classical NARP phenotype. This mutation alters the amino acid right next to canonical NARP mutation. We suggest that classic NARP syndrome relates to a defined dysfunction of p.MT-ATP6.

Limited diagnostic value of enzyme analysis in patients with mitochondrial tRNA mutations.

We evaluated the diagnostic value of respiratory chain (RC) enzyme analysis of muscle in adult patients with mitochondrial myopathy (MM). RC enzyme activity was measured in muscle biopsies from 39 patients who carry either the 3243A>G mutation, other tRNA point mutations, or single, large-scale deletions of mtDNA. Findings were compared with those obtained from asymptomatic relatives with the 3243A>G mutation, myotonic dystrophy patients, and healthy subjects. Plasma lactate concentration, maximal oxygen uptake, and ragged-red fibers/cytochrome c-negative fibers in muscle were also determined. Only 10% of patients with the 3243A>G point mutation had decreased enzyme activity of one or more RC complexes, whereas this was the case for 83% of patients with other point mutations and 62% of patients with deletions. Abnormal muscle histochemistry was found in 65%, 100%, and 85% of patients, respectively, in these three groups. The results indicate that RC enzyme analysis in muscle is not a sensitive test for MM in adults. In these patients, abnormal muscle histochemistry appears to be a better predictor ofMM.

Muscle phenotype and mutation load in 51 persons with the 3243A>G mitochondrial DNA mutation.

BACKGROUND: Mitochondrial disorders are generally not associated with a clear phenotype-genotype relationship, which complicates the understanding of the disease and genetic counseling. OBJECTIVE: To investigate the relationship between the muscle and blood mitochondrial DNA mutation load and phenotype. DESIGN: Survey. SETTING: The Neuromuscular Research Unit, Rigshospitalet, Copenhagen, Denmark. PARTICIPANTS: Fifty-one persons with the 3243A>G point mutation of mitochondrial DNA, and 20 healthy control subjects. METHODS: We recorded the maximal oxygen uptake (Vo(2)max), maximal workload, resting and peak-exercise plasma lactate levels, muscle and blood mutation load, muscle morphology, and presence of diabetes mellitus and hearing impairment in all subjects. RESULTS: Muscle mutation load (mean +/- SE, 50% +/- 5%; range, 2%-95%) correlated with Vo(2)max and resting plasma lactate level (P<.001; R>/=0.64). All persons except 5 with a muscle mutation load above 50% had abnormal Vo(2)max and morphology on muscle biopsy findings. Persons with hearing impairment and diabetes mellitus had a muscle mutation load above 65%. The mutation load in blood (mean +/- SE, 18% +/- 3%; range, 0%-61%) did not correlate with Vo(2)max, resting plasma lactate levels, or presence of hearing impairment or diabetes mellitus. CONCLUSIONS: This study demonstrates a close relationship between the muscle mutation load and phenotype in persons carrying the 3243A>G mutation. The lack of correlation between the mutation load in blood and symptoms from other tissues emphasizes the importance of assessing phenotype-genotype correlations in the same tissue in mitochondrial disease. The results indicate that the threshold of muscle mutation load at which oxidative impairment occurs can be as low as 50%, which is as much as 40% lower than that suggested by in vitro studies.